UBC Theses and Dissertations

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UBC Theses and Dissertations

A photometric study of the Seyfert galaxies NGC 1566 and NGC 1068 Monger, Patricia Aline 1980

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C • I A PHOTOMETRIC STODY OF THE SEYPERT GALAXIES HGC 1566 AND NGC 1068 by PATRICIA ALINE MONGER B.A., W i c h i t a S t a t e U n i v e r s i t y , 1975 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department o f Geop h y s i c s and Astronomy) Be a c c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e g u i r e d s t a n d a r d The U n i v e r s i t y o f B r i t i s h Columbia March, 1980 © P a t r i c i a A l i n e Monger, 1980 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t n f GBOPMSICS AMO Asr/tOAJcwy The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 W e s b r o o k P l a c e V a n c o u v e r , C a n a d a V6T 1W5 D a t e MftZCH /7, /?& i i A b s t r a c t Two d i m e n s i o n a l photometry of NGC 1068 and NGC 1566 a t v i s u a l and r e d w a velengths has baea o b t a i n e d . An H°< image o f NGC 1068 has a l s o been o b t a i n e d . D e c o m p o s i t i o n of the l u m i n o s i t y p r o f i l e s d e r i v e d from the data shows t h a t the i n n e r r e g i o n (r<18") of NGC 1566 c o n s i s t s o f a n u c l e a r p o i n t s o u r c e component, a s p h e r o i d a l b u l g e , and an e x p o n e n t i a l d i s k . C o l o r s f o r each component are d e r i v e d which show t h a t the d i s k i s redder a t t h e o u t e r edge than a t t h e c e n t e r The p o i n t s o u r c e component i s q u i t e weak, c o n t r i b u t i n g o n l y 5% o f t h e t o t a l l i g h t i n an 8^5 a p e r t u r e . A c o l o r map i s a l s o p r e s e n t e d , showing an enhancement o f r e d e m i s s i o n i n t h e c e n t e r a n d a t t h e o u t e r edges of the image. F o r NGC 1068, t h e p r o f i l e s p e r m i t a b u l g e component t o be d etermined f o r r<11". S u b t r a c t i o n o f the s e e i n g c o n v o l v e d b u l g e r e v e a l s a p o i n t s o u r c e component i n t h e red image.. T h i s f e a t u r e i s not observed i n the v i s u a l image, due t o o b s c u r a t i o n by d u s t . The c o l o r map f o r NGC 1068 shows a s t r o n g c o l o r g r a d i e n t i n t h a t t h e c e n t r a l r e g i o n i s much redder t h a n t h e o u t e r r e g i o n , f o r r<18". There i s a l s o an enhancement i n r e d l i g h t a l o n g the major a x i s t h a t may d e s c r i b e a b a r - l i k e component. i i i T a b l e Of Co n t e n t s Chapter 1. I n t r o d u c t i o n ................................... 1 1. Some O b s e r v a t i o n a l P r o p e r t i e s Of S e y f e r t G a l a x i e s .........................................1 2. O b s e r v a t i o n s And Data R e d u c t i o n s 4 3. O u t l i n e Of The T h e s i s .......3 Cha p t e r 2. NGC 1566 ..,.10 1. I n t r o d u c t i o n 10 2. P h o t o m e t r i c C a l i b r a t i o n .......................... 12 3. L u m i n o s i t y P r o f i l e s ..................18 3. D i s c u s s i o n ..46 Chapter 3. NGC 1068 , •--52 1. I n t r o d u c t i o n ......................................52 2. P h o t o m e t r i c C a l i b r a t i o n ..74 3. L u m i n o s i t y P r o f i l e s ..............................33 3. D i s c u s s i o n ......105 Chapter 3. C o n c l u s i o n s ,,.109 B i b l i o g r a p h y 111 Appendix .......119 i v L i s t Of T a b l e s Table 1. D e t e c t o r C h a r a c t e r i s t i c s ......................... 5 T a b l e 2. O b s e r v a t i o n a l Elements Of NGC 1566 12 T a b l e 3. P h o t o m e t r i c C a l i b r a t i o n Of The V Image Of NGC 1566 , . , , 14 T a b l e 3. P h o t o m e t r i c C a l i b r a t i o n Of The B Image Of NGC 1566 . ... 16 Tab l e 5. S u r f a c e B r i g h t n e s s D i s t r i b u t i o n Of The R Image Of NGC 1566 ....31 Table 6. S u r f a c e B r i g h t n e s s D i s t r i b u t i o n Of The V Image Of NGC 1566 , ,.40 T a b l e 7. Model Parameters F o r NGC 1566 #.51 Table 8. O b s e r v a t i o n a l Elements Of NGC 1068 74 T a b l e 9. P h o t o m e t r i c C a l i b r a t i o n Of The V Image Of NGC 1068 .......78 Table 10. S u r f a c e B r i g h t n e s s D i s t r i b u t i o n Of The R Image Of NGC 1068 93 Table 11. S u r f a c e B r i g h t n e s s D i s t r i b u t i o n Of The V Image Of NGC 1068 , .,.98 V L i s t Of F i g u r e s F i g . 1. C o l o r - A p e r t u r e d e l a t i o n s For NGC 1566 ... 19 F i g . 2. NGC 1566: V-r C o l o r Hap 20 F i g . 3. NGC 1566 Red Image: I s o p h o t a l C o n t o u r s ,...29 F i g . 4. NGC 1566 Red Image: L u m i n o s i t y P r o f i l e ,..30 F i g . 5. NGC 1566 Red Image: I n i t i a l Bulge Model 32 F i g . 6. NGC 1566 Red Image: F i n a l Disk flodel .....33 F i g . 7. NGC 1566 Red Image: F i n a l B u l g e Models ,34 F i g . 8. NGC 1566 Red Image: R a s i d u a l N u c l e u s ...35 F i g . 9. NGC 1666 Red Image: R e s i d u a l s 35 F i g . 10. P r o f i l e s For I Zw 21 From Kormendy (1977) 37 F i g . 11. NGC 1566 V i s u a l Image: I s o p h o t a l C o n t o u r s ........38 F i g . 12. NGC 1566 V Image: L u m i n o s i t y P r o f i l e ............. 39 F i g . 13. NGC 1566 V Image: I n i t i a l B u l g e Model ,..41 F i g . 14. NGC 1566 V Image: F i n a l D i s k Model ,,.42 F i g . 15, NGC 1566 V Image: F i n a l B u l g e Models ,.43 F i g . 16. NGC 1566 V Image: R e s i d u a l N u c l e u s 44 F i g . 17. NGC 1566 V Image: R e s i d u a l s ...45 F i g . 18. NGC 1566 Observed-Convolved Bulge R e s i d u a l s ......51 F i g . 19. NGC 1068: M a g n i t u d e - A p e r t u r e R e l a t i o n ,.80 F i g . 20. NGC 1068: C o l o r - A p e r t u r e R e l a t i o n s ...81 F i g . 21. NGC 1068: V-r C o l o r Map • ...91 F i g . 22. NGC 1068 Red Image: I s o p h o t a l C o n t o u r s .92 F i g . 23. NGC 1068 Red Image: L u m i n o s i t y P r o f i l e s ..,....,..94 v i F i g . 24. NGC 1068 Red-H* Image: L u m i n o s i t y P r o f i l e 95 F i g . 25. NGC 1068 Red-fK Image: R e s i d u a l N ucleus .....96 F i g . 26. NGC 1068 V i s u a l . Image: I s o p h o t a l C o n t o u r s 97 F i g . 27. NGC. 1068 ¥ Image: I n n e r Regions ...99 F i g . 28. NGC 1063 V Image: L u m i n o s i t y P r o f i l e s .......100 F i g . 29. NGC 1068 V Image: Bulge Hodels .101 F i g . 30. NGC 1068 V Image: R e s i d u a l s ( n u c l e a r Begion) .....10 2 F i g . 31. NGC 1069 IK Image: Comtal P i c t u r e ..,,.103 F i g . 32. NGC 1068 H°< Image: I s o p h o t a l C o n t o u r s ..104 F i g . 33. NGC 1068 Observed-Convolved Bulge R e s i d u a l s ...,,.107 F i g . 34. NGC 1068 V: L u m i n o s i t y P r o f i l e s From A p e r t u r e Photometry ., -. 122 v i i Acknowledge ments I would l i k e t o thank my t h e s i s a d v i s o r . Dr. G. Fablman, f o r s u g g e s t i n g t h e t h e s i s t o p i c , making t h e data a v a i l a b l e t o me, and e s p e c i a l l y f o r v e r y p a t i e n t l y g u i d i n g me t h r o u g h t h e a n a l y s i s . I am most a p p r e c i a t i v e o f h i s encouragement and w i l l i n g n e s s t o p r o v i d e a d v i c e whenever I asked f o r i t . Dr. C h r i s P r i t c h e t and Dr. A l f o n s o C o n d a l took t h e o b s e r v a t i o n s , d i d the p r e l i m i n a r y d a t a r e d u c t i o n , and p r o v i d e d most of t h e d a t a r e d u c t i o n s o f t w a r e , i n a d d i t i o n t o a n swering my q u e s t i o n s about the d a t a and t h e d e t e c t o r . I am g r a t e f u l t o Dr. P r i t c h e t f o r t a k i n g the time t o h e l p me with the data a n a l y s i s and s e t me on t h e r i g h t t r a c k when I found m y s e l f g u i t e c o n f u s e d . Stephenson Yang p r o v i d e d a good d e a l o f i n f o r m a t i o n about t h e U.B.C computer system, as w e l l as s h a r i n g some v e r y u s e f u l programs he had w r i t t e n . I a l s o r e c e i v e d h e l p f u l a d v i c e from Drs. G l a l k e r , P. H i c k s o n , and J . Auman, f o r which I would l i k e t o thank them, and u s e f u l c r i t i c a l comments on the t h e s i s i t s e l f from Dr. 6 . P u d r i t z , t o whom I am a l s o most g r a t e f u l . 1 Chapter J I n t r o d u c t i o n J i Some O b s e r v a t i o n a l P r o p e r t i e s Of S e y f e r t G a l a x i e s Since the f i r s t i d e n t i f i c a t i o n of S e y f e r t g a l a x i e s as a d i s t i n c t type cf o b j e c t ( S e y f e r t , 1943) there have been many s t u d i e s of s p e c i f i c g a l a x i e s c f S e y f e r t type, as well as surveys aimed at determining the freguency of occurrence of the S e y f e r t phenomenon, and understanding i t s nature. In 1968 a conference on S e y f e r t g a l a x i e s was h e l d , and the r e s u l t s (A.J.,v.73,pp 836-916) presented the f i r s t comprehensive d i s c u s s i o n of these objects..Weedman (1977) reviewed the data accumulated t o 1976, p r e s e n t i n g a t a b l e of known S e y f e r t g a l a x i e s (a t o t a l of 88, at t h a t t i m e ) . The two c h a r a c t e r i s t i c s which d e f i n e a S e y f e r t galaxy are i t s prominant s t a r - l i k e nucleus, and the presence of broad (~1000 km/s) emission l i n e s i n the spectrum. Most of the S e y f e r t s are s u f f i c i e n t l y d i s t a n t that morphological c l a s s i f i c a t i o n i s not p o s s i b l e , but those t h a t are nearby are a l l c l a s s i f i e d as s p i r a l g a l a x i e s or barred s p i r a l s , of v a r i o u s subtypes. The continuum r a d i a t i o n of S e y f e r t g a l a x i e s shows both an i n f r a r e d and u l t r a v i o l e t e x c e s s . In most cases, the a b s o r p t i o n - l i n e spectrum produced by the s t a r s i n the galaxy i s not seen, because i t i s obscured by the continuum r a d i a t i o n and emission l i n e s produced i n the c e n t r a l r e g i o n s . S e y f e r t s 2 are not i n g e n e r a l s t r o n g r a d i o s o u r c e s , a l t h o u g h some a r e , nor do t h e y appear b r i g h t i n the X-ray r e g i o n . K h a c h i k i a n and Weedman (1971) d i v i d e d S e y f e r t s i n t o two t y p e s , 1 and 2 , based on the w i d t h of the Balmer l i n e s compared t o t h e f o r b i d d e n l i n e s . F o r type 1 S e y f e r t s , t h e Balmer l i n e s are broad but t h e f o r b i d d e n l i n e s are narrower, whereas i n type 2 S e y f e r t s , the Balmer l i n e s and f o r b i d d e n l i n e s are of t h e same w i d t h . T h i s i s most e a s i l y e x p l a i n e d by the h y p o t h e s i s t h a t the f o r b i d d e n e m i s s i o n l i n e s i n S e y f e r t 1 g a l a x i e s a r i s e i n a d i f f e r e n t r e g i o n t h a n the Balmer l i n e s . There i s some e v i d e n c e as w e l l (Neugebauer,et a l , 1976) t h a t the two t y p e s of S e y f e r t s . d i f f e r i n t he n a t u r e of the observed i n f r a r e d r a d i a t i o n . F o r S e y f e r t 1 g a l a x i e s , t h i s i s thought t o a r i s e from a s y n c h r o t r o n s o u r c e i n the n u c l e u s , whereas i n S e y f e r t 2 g a l a x i e s , r e r a d i a t i o n o f th e uv photons by dust i n t h e c e n t r a l r e g i o n appears t o be a more l i k e l y e x p l a n a t i o n . T h i s s u g g e s t i o n , however, i s based on a n e c e s s a r i l y s m a l l sample of S e y f e r t s . R ieke (1978) g u e s t i o n e d t h i s p i c t u r e on the b a s i s o f h i s i n f r a r e d survey o f 5 3 S e y f e r t s . He noted t h a t i n most c a s e s i t was i m p o s s i b l e t o f i t a s i n g l e power law t o the continuum r a d i a t i o n o f a S e y f e r t g a l a x y , o f e i t h e r t y p e . I n a d d i t i o n , he c i t e s e v i d e n c e , such as t h e d e t e c t i o n of 10 micron s i l i c a t e f e a t u r e s i n 3 t y p e 1 S e y f e r t s , and t h e f a c t t h a t f o r b o t h t y p e s of S e y f e r t s , a s t e e p e r i n f r a r e d continuum i s c o r r e l a t e d w i t h a l a r g e r v a l u e f o r 0-E, t o suggest t h a t dust r e r a d i a t i o n i s a l s o a prominant s o u r c e o f the i n f r a r e d l u m i n o s i t y of t y p e 1 S e y f e r t s . 3 The n a t u r e o f the n o n s t e l l a r r a d i a t i o n s o u r c e i n S e y f e r t g a l a x i e s i s unknown. The h y p o t h e s i s t h a t the sour c e has a nonth e r m a l e m i s s i o n mechanism i s s u p p o r t e d by o b s e r v a t i o n s o f v a r i a b i l i t y i n the continuum r a d i a t i o n of s e v e r a l S e y f e r t s (e. g. L y u t y i , 1977, de V a u c c u l e u r s , 1973). T h i s a l s o i n d i c a t e s t h a t the s o u r c e i s compact, of s i z e l e s s than 1 l i g h t - y e a r . For t h e s e r e a s o n s , t h e n u c l e i of S e y f e r t g a l a x i e s a r e o f t e n c o n s i d e r e d t o be s i m i l a r t o QSO's. P o s s i b l e e x p l a n a t i o n s of the n a t u r e o f the s e o b j e c t s have been d i s c u s s e d by G i n z b u r g and Ozernoy (1977). Of i n t e r e s t i n c o n n e c t i o n w i t h the work p r e s e n t e d here i s t h e g u e s t i o n o f wbether a l l s p i r a l g a l a x i e s pass t h r o u g h a S e y f e r t s t a g e , o r whether t h e o c c u r r r e n c e of t h e S e y f e r t phenomenon i s c o r r e l a t e d w i t h s t r u c t u r a l o r e v o l u t i o n a r y p r o c e s s e s t h a t o n l y some s p i r a l s e x h i b i t . I t i s u s e f u l t h e r e f o r e t o study S e y f e r t g a l a x i e s w i t h a view t o comparing them w i t h normal s p i r a l g a l a x i e s . T h e i r s p e c t r o s c o p i c . p e c u l a r i t i e s a r e e v i d e n t , s i n c e i t i s t h e s e t h a t d e f i n e t h e c l a s s . As t o m o r p h o l o g i c a l d i f f e r e n c e s , one f e a t u r e noted by v a r i o u s o b s e r v e r s ( c f Weedman, 1977, and r e f e r e n c e s t h e r e i n ) i s t h a t some S e y f e r t s have a f a i n t o u t e r r i n g s t r u c t u r e s u r r o u n d i n g t h e d i s k . One example o f t h i s can be seen i n NGC 1068, i n the Hubble A t l a s photograph. Adams (1977) used l a r g e - s c a l e image tube p l a t e s f o r a m o r p h o l o g i c a l s t u d y of 80 S e y f e r t g a l a x i e s . I t was not p o s s i b l e t o g i v e Hubble, t y p e s f o r the g a l a x i e s , but the a r e s u l t s of the s u r v e y i n d i c a t e d t h a t S e y f e r t n u c l e i o c c u r e d i n most t y p e s of s p i r a l s and b a r r e d s p i r a l s . No more than 10% o f t h e S e y f e r t g a l a x i e s might be e l l i p t i c a l , which Adams sugg e s t e d may r e f l e c t t h e f a c t t h a t no S e y f e r t s are found i n r i c h c l u s t e r s , where e l l i p t i c a l s a re more common. The s u r v e y a l s o i n d i c a t e d a s u r p l u s of S e y f e r t n u c l e i i n p e c u l i a r g a l a x i e s . Adams c o n f i r m e d t h e o c c u r r e n c e of e x t e r n a l r i n g s i n some S e y f e r t g a l a x i e s , a l t h o u g h he noted t h a t i t cannot be determined whether the f r e g u e n c y of o c c u r r e n c e o f such s t r u c t u r e i s g r e a t e r than i n normal g a l a x i e s . A more d e t a i l e d study of the s t r u c t u r e of t h e c e n t r a l r e g i o n s of S e y f e r t g a l a x i e s might determine whether o t h e r m o r p h o l o g i c a l p e c u l i a r i t i e s e x i s t as w e l l . For t h e two S e y f e r t g a l a x i e s s t u d i e d i n t h i s t h e s i s , p a r t i c u l a r a t t e n t i o n w i l l be p a i d t o t h i s q u e s t i o n . 2. O b s e r v a t i o n s And Data S e d u c t i o n The o b s e r v a t i o n s were made on the n i g h t s of January 21 and 22, 1978, a t t h e B i t c h e y - C h r e t i e n f o c u s o f t h e 1.5m t e l e s c o p e a t C e r r o T o l o l o I n t e r - A m e r i c a n O b s e r v a t o r y , by C. P r i t c h e t and A. C o n d a l . The d e t e c t o r employed was a 400xU00 element c h a r g e - c o u p l e d d e v i c e on l o a n t o the o b s e r v a t o r y by t h e J e t P r o p u l s i o n L a b o r a t o r y , Pasedena, C a l i f o r n i a . T h i s d e v i c e has been e x t e n s i v e l y d i s c u s s e d e l s e w h e r e (Fahlman e t a l , 1978, C o n d a l , 1979, P r i t c h e t , 1979), t h e r e f o r e i t w i l l 5 s u f f i c e t o p r e s e n t here a b r i e f summary of the o p e r a t i n g c h a r a c t e r i s t i c s (Table 1) and t o p o i n t out some i m p o r t a n t f e a t u r e s of t h e system t h a t a f f e c t t h e o b s e r v a t i o n s a n a l y s e d h e r e : T a b l e Ji D e t e c t o r C h a r a c t e r i s t i c s S i z e 9x9 mm Format 400x400 p i x e l s C e n t e r - t o - c e n t e r s p a c i n g 23 m S a t u r a t i o n charge 3 x 1 0 s e" Bead-out n o i s e 27 e" O p e r a t i n g t e m p e r a t u r e -100* C S p e c t r a l range 4000A-11000A Quantum e f f i c i e n c y —709E a t 7000A, H0% at 5000A T h i c k n e s s 10/* (aj There were a number of d e f e c t i v e p i x e l s and columns of p i x e l s on the a r r a y , which l i m i t e d the u s e f u l s i z e o f t h e d e t e c t o r t o 200x200 p i x e l s . Even w i t h i n t h i s r e g i o n t h e r e were dead columns but e f f o r t s were made t o ensure t h a t the l i g h t from t h e c e n t r a l r e g i o n s o f the g a l a x y f e l l on " c l e a n " a r e a s o f the d e t e c t o r (b) The o b s e r v a t i o n s c o n s i s t e d of an o b j e c t frame, a sky frame, and a f l a t f i e l d frame. The sky frame was s u b t r a c t e d from the o b j e c t frame t c e l i m i n a t e the c o n t r i b u t i o n o f the background l i g h t and the dark c u r r e n t t o the image. The r e s u l t i n g image was then d i v i d e d by the f l a t f i e l d t o account f o r v a r i a t i o n s i n p i x e l r e s p o n s e . 6 (c) The CCD has a r e l a t i v e l y high guantum e f f i c i e n c y a t red and near i n f r a r e d w a v e l e n g t h s , so t h a t a f i l t e r was i n c l u d e d t o s u p p r e s s r e d l e a k s . Thus the f i l t e r c o m b i n a t i o n s used were not the s t a n d a r d Johnson V and B f i l t e r s , but had a very s i m i l a r bandwidth and e f f e c t i v e wavelength ( P r i t c h e t , 1979) . (d) The r e a d - o u t n o i s e o f the CCD c o r r e s p o n d s t o about 1 i n s t r u m e n t a l u n i t . Thus the n o i s e i n t h e d a t a i s dominated by the -vTT f l u c t i c n i n t h e photon f l u x , assuming a P o i s s o n d i s t r i b u t i o n f o r the photons. At h a l f - s a t u r a t i o n t h e s i g n a l - t o - n o i s e r a t i o i s about 400. T y p i c a l l y the o u t e r c o n t o u r s o f the images were at about 30 i n s t r u m e n t a l u n i t s , f o r a s i g n a l - t o - n o i s e r a t i o ^20. Two images of NGC 1566, a 2 minute exposure u s i n g t h e V f i l t e r , and a 2 minute exposure u s i n g t h e B f i l t e r , were o b t a i n e d . For NGC 1068, f o u r images were t a k e n , a 2 minute V e x p o s u r e , a 1 minute exposure i n H°<, a 1 minute R e x p o s u r e , and a 20 second E exposure. The 1 minute E exposure s a t u r a t e d the d i o d e s a t the c e n t e r of the image, so t h e c e n t r a l r e g i o n o f t h e 20 second e x p o s u r e , a p p r o p r i a t e l y s c a l e d t o account f o r the d i f f e r e n t exposure t i m e s , was combined w i t h t h e 1 minute exposure , and t h e r e s u l t i n g composite image was a n a l y z e d . . The d a t a r e d u c t i o n was done u s i n g a s o f t w a r e package w r i t t e n p r i m a r i l y by C. P r i t c h e t , t o g e t h e r w i t h r o u t i n e s w r i t t e n by A. Condal and the a u t h o r . The p r e l i m i n a r y d a t a r e d u c t i o n i n c l u d e d removing t h e dark c u r r e n t and sky 7 background, d i v i d i n g by t h e f l a t f i e l d , and r e p l a c i n g d e f e c t i v e columns of p i x e l s w i t h the i n t e r p o l a t e d mean of the s u r r o u n d i n g columns. T h i s was p o s s i b l e because t h e d e f e c t i v e columns o c c u r e d i n r e g i o n s of the image f a r enough from the c e n t e r t h a t t h e l u m i n o s i t y p r o f i l e changed o n l y s l i g h t l y from column t o column. The o r i e n t a t i o n and s c a l e s i z e of the d e v i c e was o b t a i n e d frcm o b s e r v a t i o n s of the Trapezium i n O r i o n . From t h i s a s c a l e s i z e of .415 a r c s e c / p i x e l was d e t e r m i n e d . Two methods o f d i s p l a y i n g the images have been used h e r e . Using a m o d i f i e d v e r s i o n of a program made a v a i l a b l e by t h e U n i v e r s i t y o f B r i t i s h Columbia Computing C e n t e r , c o n t o u r s o f e g u a l i n t e n s i t y were p l o t t e d f o r each image. The program a l s o c a l c u l a t e s an e f f e c t i v e r a d i u s f o r each c o n t o u r , d e f i n e d by r ={A/ff, where A i s t h e ar e a e n c l o s e d by the c o n t o u r . I n t h i s way l u m i n o s i t y p r o f i l e s were d e r i v e d . A second method of d i s p l a y , which p r e s e n t e d a s t r i c t l y g u a l i t a t i v e p i c t u r e of t h e images, was through t h e use o f the CCMTAL V i s i o n One Image P r o c e s s i n g System (Comtal C o r p o r a t i o n , Pasadena, C a l i f o r n i a ) , which i s owned by t h e Remote S e n s i n g Group a t the U n i v e r s i t y of B r i t i s h Columbia and made a v a i l a b l e f o r remote s e n s i n g a p p l i c a t i o n s . T h i s system has been d i s c u s s e d i n d e t a i l by C o n d a l e t a l , (1979). B r i e f l y , t h e images a r e d i s p l a y e d on a c o l o r t e l e v i s i o n s c r e e n which i s c o n t r o l l e d by commands e n t e r e d on an a t t a c h e d keyboard. A number o f o p e r a t i o n s can be performed on t h e images. F o r t h e 8 d i s p l a y presented here, the images were magnified, and the i n t e n s i t y l e v e l s were col o r - c o d e d to present a g u a l i t a t i v e p i c t u r e of how the i n t e n s i t y changed across the image. T h i s system proved most u s e f u l i n d i s p l a y i n g the V-E images, where a contour d i s p l a y i s d i f f i c u l t to i n t e r p r e t . The contour p l o t s and the COMTAL d i s p l a y s of each image w i l l be presented i n the subseguent c h a p t e r s , where the s a l i e n t f e a t u r e s of each image, as i l l u s t r a t e d by these d i s p l a y systems, w i l l be analyzed. 2s. O u t l i n e Of The T h e s i s The two g a l a x i e s r e p o r t e d on i n t h i s t h e s i s are NGC 1068 and NGC 1566. NGC 1068 i s a type 2 S e y f e r t and NGC 1566 i s type 1, so t h a t comparison of these two g a l a x i e s i s u s e f u l i n c o n s i d e r a t i o n of the d i f f e r e n t p h y s i c a l c o n d i t i o n s a s c r i b e d to the two types of S e y f e r t s . They are at approximately the same d i s t a n c e f o r us, which f a c i l i t a t e s a n a l y s i s and comparison o f the s t r u c t u r e of the c e n t r a l r e g i o n s . Chapter 2 w i l l d i s c u s s the o b s e r v a t i o n s of NGC 1566. The f i r s t s e c t i o n reviews tbe o b s e r v a t i o n a l s t u d i e s t h a t have been pub l i s h e d on t h i s galaxy, at o p t i c a l , i n f r a r e d , and r a d i o wavelengths. The second s e c t i o n d e a l s with the photometric c a l i b r a t i o n of the CCD o b s e r v a t i o n s , and the t h i r d s e c t i o n d i s c u s s e s the l u m i n o s i t y p r o f i l e s . In the f i n a l s e c t i o n , the r e s u l t s of the a n a l y s i s of the l u m i n o s i t y p r o f i l e s are 9 considered, and the derived s t r u c t u r a l components are compared with those of normal s p i r a l galaxies. Exactly the same outline i s followed in Chapter 3 for the discussion of NGC 1068, This galaxy has been extensively studied at a l l wavelengths, and a comprehensive review of the previous observational investigations i s given i n section 1, The photometric c a l i b r a t i o n i s discussed i n section 2, the luminosity p r o f i l e s i n section 3, and the comparison with normal s p i r a l s i s presented i n section 4. An Appendix has been included i n which the previous photometric work on NGC 1068 i s further discussed, with p a r t i c u l a r emphasis on the derivation of luminosity p r o f i l e s from the photometry. 10 Chapter 2 NGC J 5 6 6 J . i n t r o d u c t i o p This galaxy was c l a s s i f i e d as a Seyfert galaxy by de Vaucouleurs and de vaucouleurs (1961) on the basis of the presence of wide emission l i n e s of BX, H$, [b III] /\5007, and weak j~0 Ii] )\3727. Few spectroscopic or photometric studies have been made of t h i s object, despite the fact that i t i s one of the brightest Seyferts, because of i t s southerly declination (-55 p). Shobbrook (1966a) observed the nuclear emission l i n e s in NGC 1566, and measured the r a d i a l velocity. Pastoriza and Gerola (1970) reported changes in the emission spectrum, with h/S decreased and the [0 III] l i n e s enhanced r e l a t i v e to the spectra of Shobbrook and the de Vaucouleurs. Smith et a l (1972) further described the spectrum, and c l a s s i f i e d NGC 1566 as a type 1 Seyfert, that i s , one with narrow forbidden l i n e s and broad Balmer l i n e s . Osmer et a l (1974) studied the spectrum more extensively and measured i n t e n s i t i e s f o r several emission l i n e s , and reported an asymmetry i n the Hy? p r o f i l e , as well as measuring the continuum between 3390A and 7100i. Martin (1974) measured i n t e n s i t i e s of the emission l i n e s i n the wavelength region 3300& to 6750A, and again reported and 11 apparent v a r i a t i o n i n the B/] and [0 I I I ] l i n e s compared t o t h e v a l u e s o f P a s t o r i z a and G e r o l a , a l t h o u g h i t was not p o s s i b l e t o d e t e r m i n i f t h e v a r i a t i o n was i n t h e l i n e s t h e m s e l v e s , o r t h e continuum. As p o i n t e d out by Osmer e t a l , i t i s d i f f i c u l t t o p l a c e the continuum i n measuring l i n e i n t e n s i t i e s f o r the Balmer l i n e s because of t h e broad wings. I n f r a r e d o b s e r v a t i o n s o f NGC 1566 were made by G l a s s (1973), who l i s t e d JHKL photometry f o r 3 a p e r t u r e s i z e s and i n d i c a t e d t h a t t h e IE r a d i a t i o n t e n d s t o be c o n c e n t r a t e d i n t h e n u c l e u s . E a d i o o b s e r v a t i o n s have been r e p o r t e d by Cameron (1971) a t 408 MHz, Wright (1974) a t 2700 MHz, and Quintana e t a l (1975) at 20 and 22.2 GHz, who a l s o s u g g e s t t h a t t h e n u c l e u s c o u l d be a s s o c i a t e d w i t h t h e X-ray s o u r c e 30 0400-59. De Bruyn and W i l s o n (1976) d e r i v e d a 1415 MHz f l u x by assuming a power law spectrum between t h e f r e g u e n c i e s measured by Cameron and W r i g h t , but made no o b s e r v a t i o n s . O p t i c a l photometry f o r t h i s g a l a x y has been p u b l i s h e d by Shobbrook (1966b), Smith e t a l (1972), and de V a u c o u l e u r s (1973), wbo a l s o p r e s e n t e d i s o p h o t e maps and r e p o r t e d a v a r i a t i o n i n tbe n u c l e a r B magnitude, from comparison w i t h the Shobbrook and Smith et a l d a t a . T h i s r e s u l t was f u r t h e r c o n f i r m e d by the photometry o f Quintana e t a l (1975). - The g e n e r a l consensus among the o b s e r v e r s of NGC 1566 i s t h a t i t e x h i b i t s o n l y weak S e y f e r t c h a r a c t e r i s t i c s . The e m i s s i o n l i n e s a r e f a i n t compared t o those o f o t h e r S e y f e r t s (Osmer e t a l , 1974) as i s t h e n u c l e a r magnitude (de 12 V a u c o u l e u r s , 1973). The i n f r a r e d o b s e r v a t i o n s of G l a s s (1973) i n d i c a t e t h a t t h i s g a l a x y does not have a s t r o n g i n f r a r e d e x c e s s as has been d e t e c t e d i n o t h e r S e y f e r t g a l a x i e s (e. g. B i e k e and Low, 1972, Kleinmann and W r i g h t , 1974)-. T a b l e 2 ( a f t e r de V a u c o u l e u r s , 1973) summarizes t h e b a s i c f e a t u r e s of NGC 1566. Photographs have been p u b l i s h e d by Evans (1S56), S e r s i c (1957), Shobbrook (1966a), Smith e t a l (1972), and de V a u c o u l e u r s (1973). T a b l e 2 Elements Of NGC 1566 B.A. (1950) 4^18:9 Dec (1950) -55°04' 1, b 264', -43° L, B 235* , -41* Type SAB (s) be V e l o c i t y +1393 km/s Apparent magnitude 10.4 C o l o r (B-V) 0.77 Mean a x i s r a t i o 0.85 Face-on d i a m e t e r 6.'6 C o r r e c t e d v e l o c i t y +1173 km/s 2. P h o t o m e t r i c C a l i b r a t i o n 13 Because c f the e x p e r i m e n t a l n a t u r e of the JPL CCD camera, no d e t a i l e d c a l i b r a t i o n of the i n t e g r a t e d f l u x per i n s t r u m e n t a l u n i t e x i s t s . T h e r e f o r e t h e p h o t o m e t r i c c a l i b r a t i o n f o r t h e V image was a c h i e v e d by summing the p i x e l i n t e n s i t i e s w i t h i n a c i r c u l a r boundary of d i a m e t e r c o r r e s p o n d i n g t o each of the a p e r t u r e d i a m e t e r s o f the e x i s t i n g p u b l i s h e d photometry, and comparing t h i s s i m u l a t e d photometry w i t h t h e p u b l i s h e d V magnitudes. Because o f t h e n u c l e a r v a r i a b i l i t y r e p o r t e d f o r t h i s g a l a x y , i t was n e c e s s a r y t o c a l i b r a t e the photometry i n terms of a n n u l i r a t h e r t h a n c i r c u l a r a p e r t u r e s . The n u c l e a r diameter measured f o r NGC 1566 by de V a u c o u l e u r s and de V a u c o u l e u r s (1968) i s 7i'0, t h e r e f o r e t h e n u c l e u s was c o m p l e t e l y c o n t a i n e d i n t h e s m a l l e s t a p e r t u r e used i n the photometry o f Smith e t a l (1972), which was 8'i5. T a b l e 3 l i s t s t h e p h o t o m e t r i c c a l i b r a t i o n t h u s d e r i v e d . 14 Table 3 Photometric C a l i b r a t i o n Of The V Image Of NGC 1566 Ap. Diam V CCD v annulus V CCD v V-v 8^5 13. 17 -14.08 8: 5-17" 13.36 -14.23 27.59 17' 12.51 -(14.91 8."5-26" 12.62 -14.99 27. 61 26 " 12. 11 -15.38 SI'5-34" 12.16 -15.4 27. 56 34" 11.8 -15.68 Mean V-v =27.587 +0.025 mag (standard e r r o r ) = V +27.587-1. 88 mag/a^s*? 1 The only other V aperture photometry p u b l i s h e d f o r t h i s galaxy i s the photographic data of Shobbrook (1966b). He l i s t s a V=12.33 f o r aperture diameter 15l'6 and V=11.85 mag f o r a p e r t u r e diameter 28^8. Then the annular magnitude i s 12.96 mag. The simulated photometry of the CCD data g i v e s v=-14.68 f o r the same annulus, l e a d i n g to a V-v value of 27.64, i n s a t i s f a c t o r y agreement with the c a l i b r a t i o n d e r i v e d from the p h o t o e l e c t r i c photometry of Smith et a l . Prom t h i s c a l i b r a t i o n i t can be seen t h a t the n u c l e a r V magnitude has v a r i e d from t h a t determined by Smith et a l . They de r i v e d an upper l i m i t t o the n u c l e a r V magnitude by s u b t r a c t i n g from the observed l u m i n o s i t y i n the 81'5 diaphragm. 15 the l u m i n o s i t y obtained by assuming a background s u r f a c e b r i g h t n e s s egual t o t h a t observed i n the 8^5-17" annulus. From t h i s they d e r i v e d an upper l i m i t to the n u c l e a r V magnitude o f 13.5. From the c a l i b r a t i o n given i n Table 3, the background s u r f a c e b r i g h t n e s s i n the corresponding annulus f o r the CCD ob s e r v a t i o n s i n 18.94 mag/n'i T h i s leads to a background magnitude i n the 8i'5 aperture of 14.55. I f t h i s background i n t e n s i t y i s s u b t r a c t e d from the i n t e n s i t y c a l c u l a t e d f o r t h i s a p e r t u r e , the r e s u l t i n g nuclear V magnitude i s 13.69. Thus the nu c l e a r V magnitude has diminished by .19 mag s i n c e the ob s e r v a t i o n s of Smith e t a l . (1975) showed t h a t the n u c l e a r B magnitude has v a r i e d by as much as a f u l l magnitude on time s c a l e s of 1 year or l e s s . The i r r e g u l a r i t y of the ob s e r v a t i o n s of t h i s galaxy make i t i m p o s s i b l e to determine i f any p e r i o d i c i t y of v a r i a t i o n e x i s t s . Smith e t a l l i s t a formal e r r o r of .06 mag f o r t h e i r photometry. An e r r o r of t h i s s i z e i s not s u f f i c i e n t t o account f o r the disc r e p a n c y i n the photometric c a l i b r a t i o n . Quintana et a l (1975) showed that the n u c l e a r B magnitude has v a r i e d by as much as a f u l l magnitude on time s c a l e s of 1 year or l e s s . The i r r e g u l a r i t y of the o b s e r v a t i o n s of t h i s galaxy make i t i m p o s s i b l e t o determine i f any p e r i o d i c i t y of v a r i a t i o n e x i s t s . In c o n s i d e r a t i o n of the observed v a r i a b i l i t y i n the B magnitude, and of the f a c t t h a t the outer a p e r t u r e s agree i n the CCD c a l i b r a t i o n , while the inn e r one i s d i s c r e p a n t , as would be expected i f . v a r i a b i l i t y of the nucleus were the 16 source of the discrepancy, then the best explanation for the c a l i b r a t i o n results i s that the nucleus has varied. These points w i l l be further discussed i n Chapter 3, in consideration of the photometric c a l i b r a t i o n of the observations of NGC 1068. To date, there i s no published E photometry for NGC 1566. However, observations were recently made at Las Campanas, using a BCA 9658E tube, by C. HcAlary, who has kindly made the data available for c a l i b r a t i n g the CCD image. This data, and the c a l i b r a t i o n obtained, i s presented i n Table 4. Again, owing to the v a r i a b i l i t y of the nucleus, the c a l i b r a t i o n was done using annuli with inner diameter 9". Table 4 Photometric Calibration Of The B Imaqe Of NGC 1566 Ap diam E CCD r annulus E CCD r E-r 9^0 12. 836 -13.57 2225 11.280 -14.75 9"-22:5 11. 576 -14.30 25.874 29225 10.823 -15. 11 9"-29.*25 11. 008 -14.80 25.811 Mean E-r=25. 843 +.032 mag (standard error) /^,= T+25.843-1.88 mag/atwc1-The outermost simulated aperture for the CCD V image has 17 a s i g n a l - t o - n o i s e r a t i o of about 20, g i v i n g an accuracy of ±.05 mag. For the B image, the signal-to^-noise r a t i o i s about 60, f o r an accuracy of ±.02 mag. F i g u r e 1b g i v e s the B-V c o l o r - a p e r t u r e r e l a t i o n f o r NGC 1566, from the photometry of Smith et a l (1972), and t h a t l i s t e d by de Vaucouleurs and de Vaucouleurs (1968). F i g u r e 1a g i v e s the i n s t r u m e n t a l v-r c o l o r - a p e r t u r e r e l a t i o n , d e r i v e d from the s i m u l a t e d aperture photometry of the CCD data. I t i s of i n t e r e s t t o note that the l a r g e r a p e r t u r e s show a l a r g e r v - r , f o r aperture diameters >13". In a d d i t i o n , w i t h i n 8" from the c e n t e r , the v-r c o l o r i n c r e a s e s with d e c r e a s i n g a p e r t u r e s i z e . T h i s i s not s u r p r i s i n g i n view of the f a c t t h a t most S e y f e r t g a l a x i e s show an i n f r a r e d excess i n the c e n t r a l r e g i o n s . In most cases, an u l t r a v i o l e t excess i s a l s o observed, which r e s u l t s i n b l u e r B-V c o l o r s i n the c e n t r a l r e g i o n s as w e l l . There i s some i n d i c a t i o n of t h i s i n the (B-V)-aperture r e l a t i o n of NGC 1566, although the paucity of data makes t h i s s uggestion g u i t e t e n t a t i v e . I t i s the blue E-V c o l o r t h a t l e a d s to S e y f e r t n u c l e i being termed "blue n u c l e i " i n the l i t e r a t u r e , although i n f a c t most of the r a d i a t i o n from the c e n t r a l r e g i o n s i s emitted i n the i n f r a r e d . S t e i n and Weedman (1976) conclude that f o r most S e y f e r t 1 g a l a x i e s , the observed i n f r a r e d and u l t r a v i o l e t excesses are a t t r i b u t a b l e t o a nonthermal continuum source i n the n u c l e u s , while f o r S e y f e r t 2 g a l a x i e s such as NGC 1068, the i n f r a r e d excess i s probably due to thermal r e r a d i a t i o n by dust. As 18 d i s c u s s e d i n Chapter 1, t h i s s uggestion i s s t i l l open t o gu e s t i o n . Dust c l o u d s have been detected i n NGC 1068, and the V i s o p h o t a l contours presented i n Chapter 3 show a marked asymmetry i n the i n n e r r e g i o n s , which i s not observed i n the E image, and which may be a t t r i b u t e d t o the obscuring dust c l o u d s . By c o n t r a s t , no asymmetry i s noted i n the i s o p h o t a l contours of NGC 1566 ( s e c t i o n 3). The COMTAL v-r images of these g a l a x i e s (Figures 2 and 21) i l l u s t r a t e t h i s as w e l l , i n th a t the c e n t r a l , red, region of NGC 1566 i s symmetric, while that of NGC 1068 i s asymmetric. The v-r COMTAL image of NGC 1566 a l s o i l l u s t r a t e s the tre n d noted i n the ( v - r ) - a p e r t u r e r e l a t i o n , i n t h a t the c e n t r a l r e g i o n s are red, the in t e r m e d i a t e regions are b l u e r , and the outer r e g i o n s again i n c r e a s i n g l y red. T h i s p o i n t w i l l be d i s c u s s e d f u r t h e r i n d i s c u s s i o n of the l u m i n o s i t y p r o f i l e s , presented i n s e c t i o n 3. 3. Luminosity P r o f i l e s NGC 1566 i s c l a s s i f i e d i n the de Vaucouleurs system as SAB (s) be. In g e n e r a l , a s p i r a l galaxy has two main components: a d i s k , i n which the l o g of the s u r f a c e b r i g h t n e s s f a l l s o f f l i n e a r l y with r a d i u s , and a s p h e r o i d a l bulge. De Vaucouleurs (1948) found t h a t the s p h e r o i d a l component can be d e s c r i b e d by a s u r f a c e b r i g h t n e s s - d i s t a n c e r e l a t i o n of the form yLC= A+Br i l where M- i s the sur f a c e b r i g h t n e s s i n 19 / Q i 1 1 1 1_ I E ^ - l I_ .7 .g .f 1-0 I-l l-X 1-3 1-i /.? H 7^ 7^ To '<» 1-7 I* 1-1 <2<7 Figure 1: (a) v - r color-aperture r e l a t i o n of NGC 1566, derived from the simulated aperture photometry of the CCD data. Aperture diameter i s i n arcseconds. (b) B-V color-aperture r e l a t i o n . The points are from the published photometry l i s t e d i n the text, section 2. Figure 2: COMTAL p i c t u r e of the c o l o r map of NGC 1566. The reddest areas are those w i t h l a r g e s t v - r , and the white ares are those w i t h s m a l l e s t v - r . 21 mag/ (arcsec) z . Kormendy (1977) has p o i n t e d out t h a t the s p h e r o i d a l component i n many c a s e s c o n t r i b u t e s s i g n i f i c a n t l y t o t h e b r i g h t n e s s at l a r g e r a d i i . T h e r e f o r e t h e two components o f the l u m i n o s i t y p r o f i l e must be s e p a r a t e d i n o r d e r t o determine t h e parameters d e s c r i b i n g t h e d i s k and bulge s t r u c t u r e . For t h e data p r e s e n t e d h e r e , t h e d e c o m p o s i t i o n was done i n an i t e r a t i v e method, f o l l o w i n g the procedure o u t l i n e d by Kormendy (1977): (1) F i t t h e d a t a t o a d i s k p r o f i l e a t t h e o u t e r r a d i i ( r > 11") . (2) S u b t r a c t the d i s k p r o f i l e from the o b s e r v a t i o n s t o get a r e s i d u a l bulge ( 3 ) F i t a de V a u c o u l e u r s b u l g e p r o f i l e t o t h e r e s i d u a l b u lge a t i n t e r m e d i a t e r a d i i (1.2< r ^ O . 4 f o r t h e r e d image, 1.35< r'/<,<1.55 f o r t h e v i s u a l image). (4) S u b t r a c t t h e b u l g e p r o f i l e from the o b s e r v a t i o n s t o determine a r e s i d u a l d i s k . (5) f i t t h i s r e s i d u a l d i s k t o a new d i s k p r o f i l e . (6) i t e r a t e from s t e p 2. The bulge was f i t t e d t o a de V a u c o u l e u r s law a t i n t e r m e d i a t e r a d i i because a t s m a l l r a d i i s e e i n g e f f e c t s must be c o n s i d e r e d . In t h i s r e g i o n s e e i n g e f f e c t s cause the p r o f i l e t o d e v i a t e from a s t r a i g h t l i n e l o g I - v s - r r e l a t i o n . The i t e r a t i v e procedure i s used t o s e p a r a t e t h e s e e i n g c o n v o l v e d (observed) bulge from t h e d i s k . I n t h e r e g i o n where t h e d i s k 22 model i s f i t t e d , the seeing convolved bulge follows the observed deVaucouleurs law, although the parameters of the unconvolved bulge law w i l l d i f f e r s l i g h t l y from the observed r e l a t i o n . The contour map for the red image of NGC 1566 i s shown i n Figure 3. This map was produced using the contour routine described in Chapter 1. The image was smoothed with a 3x3 running mean smoothing prior to analysis. Table 5 gives the surface brightness d i s t r i b u t i o n for the r e d image, which i s plotted in Figure a . Figure 5 shows the i n i t i a l r esidual bulge p r o f i l e . The i t e r a t i v e f i t t i n g procedure was stopped when the parameters of the f i t t i n g functions changed by less than .01 i n successive i t e r a t i o n s . Figure 6 shows the f i n a l i t e r a t i o n disk p r o f i l e for the red image, and Figure 7 shows the f i n a l bulge p r o f i l e . It can be seen that the f i n a l bulge p r o f i l e i s very well determined over the entire f i t t i n g region. The disk i s less well determined, but the f i t i s within 2l.57« over the f i t t i n g region. In order to examine the inner region of NGC 1566, i t i s necessary to correct the f i n a l bulge p r o f i l e for seeing e f f e c t s . The seeing p r o f i l e was determined from a foreground star superimposed on the image cf the galaxy about 15" east of the center, which can be seen e a s i l y on the Cordoba plate published by de Vaucouleurs (1973, Plate 2). The star image was corrected to account for the background intensity of the galaxy, by subtracting from the star image the expected galaxy 23 b r i g h t n e s s at t h a t d i s t a n c e from t h e c e n t e r , determined from t h e i n i t i a l l u m i n o s i t y p r o f i l e . The r e s u l t i n g p r o f i l e i s p l o t t e d i n F i g u r e 8. That t h i s r e p r e s e n t s the a c t u a l s e e i n g p r o f i l e can be seen from c o n s i d e r a t i o n of F i g u r e 3. The d a s h e d - l i n e p a r t of the c o n t o u r s r e s u l t from r e p l a c i n g t h a t p a r t of the image w i t h t b e e x p e c t e d g a l a x y i n t e n s i t y . The c o r r e c t e d r e g i o n f i t s g u i t e w e l l t o the t r u e c o n t o u r s . The e f f e c t o f s e e i n g on the bulge p r o f i l e was determined by g e n e r a t i n g a 2 - d i m e n s i o n a l , s p h e r i c a l l y symmetric bulge model, d e t e r m i n e d from the f i n a l b u l g e p r o f i l e , and c o n v o l v i n g i t w i t h a 2 - d i m e n s i o n a l , s p h e r i c a l l y symmetric s t a r image. For t h e i n n e r 9 a r r a y elements of the bulge model, i t was n e c e s s a r y t o account f o r the e f f e c t s o f the s a m p l i n g i n t e r v a l on t h e d a t a , s i n c e the r / t law changes r a p i d l y near r=0. T h i s was done by d i v i d i n g each of t h e s e a r r a y e lements i n t o a 100x100 a r r a y o f s u belements, and a v e r a g i n g the i n t e n s i t y d etermined f o r each subelement from the r law o v e r the e n t i r e a r r a y element. The l u m i n o s i t y p r o f i l e o f the c o n v o l v e d model was t h e n compared to the f i n a l b u lge p r o f i l e , and t h e unconvolved model bulge parameters were a d j u s t e d u n t i l the model p r o f i l e f i t t e d the f i n a l p r o f i l e , a f t e r c o n v o l u t i o n . The c o n v o l v e d model p r o f i l e i s shown i n F i g u r e 7._ I t was found t h a t a bulge model w i t h s u r f a c e b r i g h t n e s s d i s t r i b u t i o n of t h e form - /A 33? +^ 723 r* H , (i) a f t e r c o n v o l u t i o n w i t h the s e e i n g d i s k , f i t t h e observed 24 p r o f i l e as determined from the i t e r a t i v e p r o c e d u r e . E q u a t i o n (1) i s lower i n s l o p e and i n t e r c e p t t h a n t h e s t r a i g h t l i n e o f F i g u r e 7, but a f t e r c o n v o l u t i o n t h e f i t i s v e r y good. T h i s i n d i c a t e s t h a t t h e s e e i n g a f f e c t s the p r o f i l e even a t d i s t a n c e s of s e v e r a l arcseconds from t h e c e n t e r . The c o n v o l v e d bulge was then s u b t r a c t e d from t h e o b s e r v a t i o n s f o r t h e r e d image, and the r e s i d u a l s were examined. F i g u r e 9 shows the r e s i d u a l p r o f i l e , which c o n s i s t s o f a d i s k - t y p e p r o f i l e , d e t e r m i n e d from t h e i t e r a t i o n p r o c e d u r e , w i t h a s u r f a c e b r i g h t n e s s d i s t r i b u t i o n o f t h e form y ^ e = '7- -t~. 03/? 7r . and a s t a r - l i k e n u c l e u s . T h i s n u c l e u s p r o f i l e , a f t e r s u b t r a c t i n g t h e d i s k , i s p l o t t e d i n F i g u r e 8. I t can be f i t t e d t o a G a u s s i a n i n t e n s i t y d i s t r i b u t i o n o f the form However, t h e n u c l e u s i s g u i t e f a i n t , c o n t r i b u t i n g about 5% of t h e l u m i n o s i t y i n s i d e an 81'5 d i a m e t e r c i r c u l a r r e g i o n . T h i s seems i n k e e p i n g w i t h the observed weakness o f the S e y f e r t c h a r a c t e r i s t i c s of NGC 1566. The d i s k p r o f i l e f i t s t he s t r a i g h t l i n e r e l a t i o n t o w i t h i n 4X a t a l l r a d i i . There appears t o be some r e g u l a r i t y i n the way the observed p o i n t s o s c i l l a t e about t h e s t r a i g h t l i n e . An attempt t o determine i f t h i s t r e n d was s i g n i f i c a n t was made, by s u b t r a c t i n g the c o n v o l v e d bulge and t h e s t a r - l i k e n u c l e u s from the o b s e r v a t i o n s , i n the f u l l 2 - d i m e n s i o n a l s e n s e , and examining the r e s u l t i n g d i s k . No s y s t e m a t i c t r e n d 25 was e v i d e n t from t h e d i s k c o n t o u r s , and s i n c e t h e d e v i a t i o n i s so s m a l l , i t i s not p o s s i b l e t o a s c r i b e any s i g n i f i c a n c e t o t h e s e o s c i l l a t i o n s . F i g u r e 18 shows the observed minus c o n v o l v e d r e s i d u a l s f o r the b u l g e components o f the r e d and v i s u a l images o f NGC 1566. F o r t h e r e d image, o~=.019, and f o r the v i s u a l image, <o=.016. The under-luminous r e g i o n o f t h e red image (7"<r<10 M) can t h e r e f o r e be seen t o be m a r g i n a l l y s i g n i f i c a n t , a l t h o u g h a t t h e s e r a d i i the d i s k component dominates, so the c o n c l u s i o n s a r e a l s o a f f e c t e d by e r r o r s i n t h e d e t e r m i n a t i o n of t h i s component. I t i s of i n t e r e s t t o compare the r e s u l t s o b t a i n e d here w i t h t h o s e of Kormendy (1977) who a n a l y z e d s e v e r a l r e d compact g a l a x i e s u s i n g the same p r o c e d u r e . The r e s u l t s o f h i s d e c o m p o s i t i o n i n d i c a t e d t h a t t h e s p h e r o i d became s t e e p e r w i t h s u c c e s s i v e i t e r a t i o n s . I n the r e s u l t s p r e s e n t e d h e r e , however, both the s p h e r o i d and the d i s k become s h a l l o w e r . A more s i g n i f i c a n t d i f f e r e n c e i n t h e r e s u l t s of the d e c o m p o s i t i o n i s t h a t Kormendy found t h a t the best f i t t i n g d e c o m p o s i t i o n o f the p r o f i l e w as.obtained i f the d i s k was modeled as c u t t i n g o f f s h a r p l y at s m a l l r a d i i . The u n d e r l y i n g d i s k p r o f i l e s he p r e s e n t s i n h i s F i g u r e s 3 and 6 (reproduced i n F i g u r e 10 o f t h i s work) show a d i s k t h a t d e v i a t e s from an e x p o n e n t i a l a t r a d i i <15". T h i s t y p e of model was m o t i v a t e d by t h e f a c t t h a t , i n t h e i t e r a t i o n p r o c e d u r e , t h e sum of the two components r e s u l t e d i n a p r o f i l e t h a t was o v e r - l u m i n o u s between 5" and 26 15", compared t o t h e o b s e r v a t i o n s . The data p r e s e n t e d here do not suggest a c u t o f f i n the d i s k a t s m a l l r a d i i . However, as d i s c u s s e d p r e v i o u s l y , the t r e n d o f the d i s k becoming l e s s e x p o n e n t i a l w i t h s u c c e s s i v e i t e r a t i o n s i s o b s e r v e d . But r a t h e r t h a n d e r i v i n g a s i n g l e under-luminous r e g i o n i n t h e d i s k model a t i n t e r m e d i a t e r a d i i , as Kormendy f o u n d , the d i s k p r o f i l e i s s u c c e s s i v e l y under- and o v e r - l u m i n o u s compared t o the e x p o n e n t i a l model. By p o s t u l a t i n g a d i s k c u t o f f a t r ^ 5 " , as Kormendy does, i t would be n e c e s s a r y t o a s c r i b e a l l t h e e x c e s s l u m i n o s i t y i n s i d e t b a t r a d i u s , a f t e r s u b t r a c t i n g t h e b u l g e from th e observed p r o f i l e , t o t h e n u c l e a r component. Such a component c o u l d not be f i t t e d to a G aussian model. The v i s u a l image of NGC 1566 was a n a l y z e d i n t h e same manner as the red image. The c o n t o u r p l o t i s shown i n F i g u r e 11, and t h e c o r r e s p o n d i n g l u m i n o s i t y p r o f i l e i s t a b u l a t e d i n T a b l e 6 # and p l o t t e d i n F i g u r e 12. I t can be seen from the c o n t o u r p l o t t h a t the v i s u a l image i s much n o i s i e r t h a n the r e d image. The v i s u a l image was smoothed w i t h a 4x4 r u n n i n g mean smoothing. The i n i t i a l b u l g e p r o f i l e i s shown i n F i g u r e 13, t h e f i n a l d i s k p r o f i l e i n F i g u r e 14, and t h e f i n a l b u l g e i n F i g u r e 15. The f i n a l d i s k p r o f i l e d e v i a t e s even more from the e x p o n e n t i a l than t h e red image does. However, as mentioned, the v i s u a l image i t s e l f i s n o i s i e r than the r e d image so i t c a nnot be c o n c l u d e d t h a t t h i s r e p r e s e n t s any r e a l d i f f e r e n c e i n t h e v i s u a l and r e d d i s k s . 27 The s e e i n g p r o f i l e i s p l o t t e d i n f i g u r e 16. T h i s p r o f i l e i s Gaussian out to r =2", with a seeing d i s k diameter (FWHM) of 2^48. The v i s u a l image bulge was c o r r e c t e d f o r seeing e f f e c t s i n the same manner as the red image. I t was found t h a t c o n v o l v i n g a bulge model with s u r f a c e b r i g h t n e s s of the form with the seeing d i s k provided a good f i t to the f i n a l i t e r a t i o n bulge p r o f i l e . T h i s convolved p r o f i l e i s shown i n F i g u r e 15. The r e s i d u a l p r o f i l e , obtained by s u b t r a c t i n g the convolved bulge frcm the o b s e r v a t i o n s , i s shown i n Figure 17. The r e s i d u a l d i s k i s f i t t e d by a s u r f a c e b r i g h t n e s s d i s t r i b u t i o n given by The r e s i d u a l n u c l e u s , obtained by s u b t r a c t i n g the convolved bulge and the d i s k from the o b s e r v a t i o n s , i s shown i n F i g u r e 16. Again, the nucleus f o l l o w s a Gaussian p r o f i l e , of the form The f a i n t n e s s of the nucleus i s s i g n i f i c a n t i n c o n s i d e r a t i o n of the observed v a r i a b i l i t y of the n u c l e a r b r i g h t n e s s of NGC 1566. From the d i s c u s s i o n i n s e c t i o n 2, the observed V magnitude i n s i d e an 8.5 aperture i s .19 mag f a i n t e r now than i n the o b s e r v a t i o n s of Smith e t a l (1972).. The s t a r - l i k e n u c l e a r component of NGC 1566 accounts f o r about 5% of the t o t a l l u m i n o s i t y i n s i d e an 8^ '5 a p e r t u r e . Thus, i f the 28 brightness variation i s e n t i r e l y due to the s t a r - l i k e nucleus, then t h i s nucleus must have been about 6 times brighter i n 1972 than i n 1977. Considering that the data of Quintana et a l (1975) indicates that the brightness variations occur on time scales of one year or l e s s , the varying component must be small, so i t would seem that the most l i k e l y source of the var i a t i o n i s the s t a r - l i k e nucleus. Brightness variations of factors comparable to th i s have been noted in other compact sources, s p e c i f i c a l l y QSO's. 21 /OO Figure 3: Isophotal contours for the red image of NGC 1566. Contour values and corresponding radii are given in Table 5. The dashed-line region indicates the region corrected to remove the foreground star, which was then used to determine the seeing profile. 30 Figure 4: Luminosity p r o f i l e for the red image of NGC 1566, derived from the values i n Table 5. The straight l i n e i s the i n i t i a l disk p r o f i l e used i n the i t e r a t i o n procedure, and i s described by the equation At* " H.57 +• .Of85r 31 Table 5 Surface Brightness Di s t r i b u t i o n Of The E Image Of NGC 1566 (arcsec) (mag/a" ) 0.73 15.79 0.92 15.88 1.09 15.97 1.25 16.06 1.41 16. 15 1.56 16.24 1.71 16.33 1.87 16.42 2.03 16.51 2. 20 16.60 2. 38 16.69 2.57 16.78 2.79 16.87 3.03 16.97 3. 30 17.06 3.60 17. 15 3..S4 17.24 4.33 17.33 4.77 17.42 5,. 29 17.51 5.89 17.60 6. 51 17.69 7.25 17.78 8.03 17.87 8.99 17.96 10. 14 18.05 11.55 18. 14 13.49 18. 23 15.43 18.32 32 2.0 Figure 5: Residual bulge profile obtained by subtracting the i n i t i a l disk from the observations. The straight line is the i n i t i a l bulge profile, described by the equation which was subtracted from the observations in the iterative procedure. 33 Onoj/a") 17.91 /?.0l-\ 11% /fci- 1 1 1 1— 0 . 0 3 . 0 6 . 0 9 . 0 _ 1 2 . 0 RflD (flRCSEC 15.0 16 Figure 6: F i n a l disk p r o f i l e (8th i t e r a t i o n ) . The s t r a i g h t l i n e i s described by the equation jU.A ~- i 7. 9</f + .03/?7r j y /57/H fit. S02l-\ T 1 r 1.2 1.4 1.5 RXX0.25 (flRCSEC) r 1.8 1 2 .0 Figure 7: NGC 1566 red image. The dots (•) indicate the final (8th) iteration bulge profile. The straight line is described by the equation The points lying below the straight line at 1.6 r 1.8 are also under-luminous on the disk profile of Figure 6. The crosses (*) indicate the convolved bulge profile, obtained from the procedure described in section 3. -35 n3(A o. Figure 8: Red star image and nucleus of NGC 1566. The dots(») denote the star profile. The straight line is described by the equation = /C.505 * -GSO?^ The crosses(*) denote the residual profile, and the corresponding straight line is described by it. 7/H 1 1 1 1 1 1 0 0 3 . 0 6 . 0 9 . 0 1 2 . 0 1 5 . 0 1 8 . 0 RflD (RRCSEC) Figure 9: Residual p r o f i l e , obtained by su b t r a c t i n g the convolved bulge p r o f i l e f o r the red image from the observed p r o f i l e . The s t r a i g h t l i n e i s that of Figure 6. 37 r (arcsec) Figure 10: From Kormendy (1977). The top figure shows the decomposition using the iterative procedure. The bottom figure is the profile obtained by fi t t i n g the disk to an equation of the form Figure 11: Isophotal contours for the v i s u a l image of NGC 1566. Contour values and corresponding r a d i i are given i n Table 6. The dashed-lines indicate the region corrected to remove the foreground star. 39 /72/-i mi A MA n-iiA 10.2.1-K K 1 1 1 0 . 0 3 . 0 6 . 0 9 . 0 RflD CflRCSEC) 1 2 . 0 1 5 . 0 1 6 . 0 Figure 12: Luminosity profile for the visual image of NGC 1566, derived from the values in Table 6. The straight line is the i n i t i a l disk profile used in the iteration procedure, and is described by the equation Mv- t .0?0/r no Table 6 Surface Brightness Dis t r i b u t i o n Of The V Image Of NGC 1566 r (arcsec) (mag/a) 0.89 17. 30 1.28 17.40 1.58 17.49 1.86 17.59 2. 11 17.68 2.36 17.78 2.60 17.87 2.85 17.97 3. 10 18.07 3.36 18. 16 3.63 18.26 3.92 18.35 4. 24 18.45 4.59 18.54 4.98 18.64 5.39 18.73 5.85 18.83 6.33 18.92 6.8 5 19.02 7.46 19.11 8.09 19.21 8.75 19.31 9.45 19.40 10.26 19.50 11. 18 19.59 12.42 19.69 1 3. 6 2 19.78 1 4.88 19.88 15.99 19.97 17.45 20.07 Figure 13: Residual bulge p r o f i l e f o r the v i s u a l image of NGC 1566, obtained by subtracting the i n i t i a l d i s k from the observations. The s t r a i g h t l i n e i s the i n i t i a l bulge p r o f i l e , described by the equation Xv'- + (..15 HA. tficA m a Qo.cxA J04J °'° 5 6"° RRD lA&SEC) 1 . . Figure 14: Final disk profile for the V image (12th iteration) the straight line i s described by the equation Mv - /f.632 t .01l7r 15.71 Figure 15: NGC 1566 visual image. The dots(») indicate the final (12th) iteration bulge profile. The straight line is described by the equation X v = /2.316- * H.SMr* The crosses(<) denote the convolved bulge profile, obtained as described in section 3. tt%-\ jQ.%-\ 0.0 1 7.0 Figure 16: Visual star image and nucleus of NGC 1566. The dots(») the star profile. The straight line is described by the equation The crosses(«) indicate the residual nucleus, and the corresponding straight line is described by f l % - \ JO.%-\ 1 1 1 1 1 1 0.0 3.0 6.0 9.0 12.0 15.0 18.0 RAD (flRCSEC) Figure 17: Residual p r o f i l e f o r the V image, obtained by subtracting the convolved bulge from the observations. The s t r a i g h t l i n e i s that of Figure 14. o 46 4. D i s c u s s i o n I t i s n e c e s s a r y t o p r e f a c e a d i s c u s s i o n of t h e s t r u c t u r e d e r i v e d here w i t h t h e warning t h a t the o b s e r v a t i o n s o n l y e x t e n d t o r ^ 1 7 " . J t would be v e r y u s e f u l t o be a b l e t o examine the p r o f i l e at l a r g e r v a l u e s of r , i n o r d e r t o b e t t e r d e t e r m i n e t h e d i s k p r o f i l e . However, no l u m i n o s i t y p r o f i l e o f NGC 1566, i n V o r E, i s a v a i l a b l e , and i n c o n s i d e r a t i o n o f the problems d i s c u s s e d i n the Appendix r e g a r d i n g d e r i v a t i o n o f the l u m i n o s i t y p r o f i l e from the e x i s t i n g photometry, a t t e m p t i n g t o f i t t h e d a t a t o a d i s k d e r i v e d from the Smith e t a l (1972) photometry would be of d o u b t f u l v a l u e . D e s p i t e t h i s d i f f i c u l t y , the p r o f i l e s o b t a i n e d from the i t e r a t i v e procedure a l l o w w e l l d e f i n e d d i s k , b u l g e , and n u c l e u s components t o be d e r i v e d . I t i s of i n t e r e s t t o compare t h e s t r u c t u r a l components of the v i s u a l and r e d images, and t o c o n s i d e r t h e s i m i l a r i t y of t h e s e components t o t h e d i s k and b u l g e components of normal s p i r a l g a l a x i e s . The most s u r p r i s i n g f e a t u r e o f the l u m i n o s i t y p r o f i l e s i s t h a t comparison of t h e s l o p e s of the v i s u a l and r e d d i s k p r o f i l e s i n d i c a t e s t h a t the d i s k i s r e d d e r a t l a r g e r r a d i i . The b u l g e , on the o t h e r hand, i s b l u e r . The d i s k component b e g i n s t o dominate the b r i g h t n e s s p r o f i l e a t r >4i!5. Thus the i n c r e a s e i n v - r c o l o r w i t h i n c r e a s i n g d i s t a n c e seen i n F i g u r e s 1a and 2 can be a t t r i b u t e d t o t h e r e d d e n i n g of t h e d i s k a t l a r g e r a d i i . 47 The magnitudes of t h e b u l g e component i n s i d e a 40" a p e r t u r e , from the c a l i b r a t i o n o f s e c t i o n 2 r are V=12,54, E=11.78. For' the d i s k , V-12.42 and R=10.62 i n s i d e t h i s a p e r t u r e . The d i s t a n c e e s t i m a t e d f o r NGC 1566 (de V a u c o u l e u r s , 1973) i s 11 Mpc. T h i s i m p l i e s , from E g u a t i o n ( 2 ) , a d i s k s c a l e l e n g t h of °<' = 1.81 kpc f o r the r e d image, and from E g u a t i o n (5) a s c a l e l e n g t h °^ ' = 1.42 kpc f o r the v i s u a l image. T h i s i s w i t h i n range of t h e s c a l e l e n g t h s f o r l a t e - t y p e s p i r a l g a l a x i e s g i v e n by Freeman (1975), who notes g e n e r a l l y low v a l u e s of °< , l e s s than 2 kpc, f o r systems of type Sbc o r l a t e r . However, t h i s s c a l e l e n g t h c o r r e s p o n d s t o about 30,/ f o r the red image, and 24" f o r t h e v i s u a l image. T h e r e f o r e i t i s i m p o s s i b l e to determine whether t h i s i s a t r u e d i s k component. DeVaucouleurs (1973) d e r i v e d a l u m i n o s i t y p r o f i l e f o r the B image of NGC 1566 from the magnitude a p e r t u r e r e l a t i o n , as d e s c r i b e d i n h i s Appendix B, and b r i e f l y d i s c u s s e d i n the Appendix to t h i s work. He f i t t e d an e x p o n e n t i a l l u m i n o s i t y d i s t r i b u t i o n t o the p r o f i l e , w i t h a s c a l e l e n g t h of 3.3 kpc. However, t h i s a n a l y s i s d i d not account f o r a bulge s t r u c t u r e i n t h e g a l a x y , a l t h o u g h as n o t e d by d e V a u c o u l e u r s , "The s m a l l but s y s t e m a t i c d e p a r t u r e s between the observed B< j ( / > ) and the pure e x p o n e n t i a l i n d i c a t e s t h e presence of a s i g n i f i c a n t c o n t r i b u t i o n from a s p h e r o i d a l component, c o n s i s t e n t w i t h the i n t e r m e d i a t e Hubble type of t h e g a l a x y . " The d i s k d e r i v e d by d eVaucouleurs was f i t t e d over a much 48 l a r g e r r e g i o n ( 3 minutes of a r c ) , so t h a t h i s da t a e x t e n d s over more than 3 d i s k s c a l e l e n g t h s . I t i s i n t e r e s t i n g t h a t t h e i n n e r 60" of the p r o f i l e he d e r i v e d , p l o t t e d i n h i s F i g u r e 11, shows a second g u a s i - e x p o n e n t i a l l u m i n o s i t y d i s t r i b u t i o n . The r e g i o n between 6" and 18" i s under-luminous compared t o t h i s i n n e r e x p o n e n t i a l , i n c o n t r a s t to the p r o f i l e s d e r i v e d from t h e CCD d a t a , but t h e p h o t o g r a p h i c d a t a used by deVauc o u l e u r s does not r e s o l v e the i n n e r r e g i o n s s u f f i c i e n t l y t o p e r m i t d e t a i l e d comparison of t h e p r o f i l e s . The n u c l e a r p o i n t s o u r c e f o r each image c l o s e l y f o l l o w s t h e s l o p e o f the Gaus s i a n p a r t o f the s t a r p r o f i l e so t h a t t h e d i f f e r e n c e i n s l o p e between t h e n u c l e a r components of the two images i s a t t r i b u t a b l e t o s e e i n g e f f e c t s . The n u c l e a r E magnitude, u s i n g t h e c a l i b r a t i o n of s e c t i o n 2, i s 16.03 and the V magnitude i s 16.73 g i v i n g a V-E c o l o r of 0.7. The magnitude of the bulge i n s i d e a 10* a p e r t u r e i s V=13.61, E=12.63. The d i s k b r i g h t n e s s i n s i d e t h i s a p e r t u r e i s V=15.05, E=13.33, so t h e n u c l e u s i s s i g n i f i c a n t l y b l u e r t h a n e i t h e r the d i s k or b u l g e . From the c a l i b r a t i o n g i v e n by Johnson (1966), the f l u x of t h e n u c l e a r component i s 1.166x10~ 2 9 W m - 2 H z - 1 a t t h e e f f e c t i v e wavelength of t h e E band, and 7.743x10 - 3° W m - 2 Hz"* at t h e e f f e c t i v e wavelength o f the V band. I f the n u c l e a r continuum i s n o n - t h e r m a l , the c o r r e s p o n d i n g s p e c t r a l i n d e x i s e<=-1.714, which i s ccmparable t o t h e s p e c t r a l i n d e x o f -2 d e r i v e d b y ; S h i e l d s and Oke (1975) f o r NGC 1068.. 49 The c o l o r diagrams ( F i g u r e s 1a and 2) show a reddened c e n t e r , due t o t h e f a c t t h a t the bulge i s redder a t the c e n t e r . As d i s c u s s e d i n s e c t i o n 2, t h i s i s p r o b a b l y n o t an e f f e c t due t o d u s t because t h e r e i s no o b v i o u s asymmetry i n t h e c o n t o u r s , and the d i s k shows the o p p o s i t e e f f e c t i n t h a t t h e o u t e r d i s k i s r e d d e r than t h e i n n e r d i s k . NGC 1566 i s a b a r r e d s p i r a l g a l a x y . However, t h e bar component does not appear to s i g n i f i c a n t l y a f f e c t the l u m i n o s i t y p r o f i l e s or t h e c o n t o u r shapes i n t h e i n n e r r e g i o n s o f the g a l a x y . Perhaps t h e w r i g g l y b e h a v i o r of t h e d i s k p r o f i l e s i s due t o the c o n t r i b u t i o n of t h i s a d d i t i o n a l component of the s t r u c t u r e which has not been c o n s i d e r e d i n t h i s a n a l y s i s . Another i m p o r t a n t a s p e c t t o c o n s i d e r i s t h e e f f e c t o f t h e e m i s s i o n l i n e s on t h e photometry. Csmer e t a l (1974) measured a f l u x through a 10" a p e r t u r e of 7 . 1 x 1 0 - 1 3 e r g s c m - 2 s ' 1 f o r t h e H°< e m i s s i o n of NGC 1566. T h i s was t h e s t r o n g e s t measured l i n e , by more th a n a f a c t o r o f 2. With t h e c a l i b r a t i o n o f Johnson (1966) the f l u x of the CCD r e d image t h r o u g h t h e same a p e r t u r e i s 5 . 2 9 6 x 1 0 - 1 1 e r g s c m - 2 s-», so t h e e m i s s i o n l i n e s c o n t r i b u t e no more than 1% o f t h e f l u x . A f i n a l p o i n t t o be c o n s i d e r e d b e f o r e a c c e p t i n g t h e s t r u c t u r e d etermined from t h i s method i s t h a t t h e b u l g e dominates i n b r i g h t n e s s i n t h e c e n t r a l r e g i o n s of the g a l a x y . T h e r e f o r e , t h e d e t e r m i n a t i o n o f the p o i n t s o u r c e component i s s t r o n g l y dependent on t h e a c c u r a c y w i t h which t h e bulge has 50 been determined. The de Vaucouleurs law d e s c r i b i n g the s p h e r o i d a l bulge s t r u c t u r e i s e m p i r i c a l l y a good approximation. However, as has been pointed out i n p r e v i o u s work (see e. g. King, 1978), t h i s r e l a t i o n cannot hold at r=0, s i n c e i t i m p l i e s an i n f i n i t e c e n t r a l d e n s i t y . Nonetheless, i t appears t o hold to r e g i o n s w e l l w i t h i n the s e e i n g d i s k , a f t e r c o r r e c t i o n f o r seeing e f f e c t s (see Schweizer, 1979). Recently, however, deVaucouleurs and C a p a c c i o l i (1979) used a convolved r law to t r y to f i t the l u m i n o s i t y p r o f i l e of the E1 galaxy NGC 3379. They d i s c o v e r e d an excess i n the c e n t r a l r e g i o n which c o u l d be accounted f o r by a Gaussian c o r e , but with a d i s p e r s i o n of 3i'7, compared t o the d i s p e r s i o n f o r the s e e i n g f u n c t i o n of 1'i3, so t h a t the excess could not be a t t r i b u t e d to a s t a r - l i k e nucleus. However, as noted p r e v i o u s l y , the Gaussian center of NGC 1566 does f o l l o w the s e e i n g p r o f i l e ^ so t h a t i t i s reasonable t c a t t r i b u t e t h i s excess t o a p o i n t source component. Eut i n c o n s i d e r a t i o n of the f a c t t h a t the deVaucouleurs law i s net p h y s i c a l l y meaningful at r=0, the u s e f u l n e s s of the c o n c l u s i o n s drawn would be i n c r e a s e d i f a more r e a l i s t i c model, such as t h a t d e r i v e d by King (1966) were used i n the i t e r a t i o n procedure. I t should be noted, though, as pointed cut by King (1978), t h a t t h i s model, which was d e r i v e d from an i s o t h e r m a l model f o r s t a r c l u s t e r s , has l i m i t a t i o n s when a p p l i e d to e l l i p t i c a l g a l a x i e s due to the d i f f e r e n t dynamics which these o b j e c t s are expected t o e x h i b i t . Because of t h i s , and because of the d i f f i c u l t y of 51 g e n e r a t i n g King models, no attempt has been made t o use them i n t h i s work. Ta b l e 7 summarizes the p h o t o m e t r i c d e c o m p o s i t i o n o f NGC 1566. T a b l e 7 Model Parameters F o r NGC 1566 j _ V image R image V star R star point source ^ _ /tf,259 M-Mo * <ra SEEING - = „ * z .(.19 Mt= H..SOS <* = .G502 SEEING_ (FN/YHMT ''SI Bulge component Mo =/2.%%3. " ' A " * * fi j3 -1-73.1 disk comp on en t. H° =/?•<# 3 _2. A> =/7.9?9 b '.03/97 - loi u tencjth "/•«/ fyZ-52 Chapter 3 NGC J068 j . I n t r o d u c t i o n NGC 1068 was i n c l u d e d i n S e y f e r t * s (1943) o r i g i n a l l i s t of 12 g a l a x i e s which he c h a r a c t e r i z e d as having "...many h i g h - e x c i t a t i o n emission l i n e s l o c a l i z e d i n the n u c l e i . . . t h e i r most c o n s i s t a n t c h a r a c t e r i s t i c being an e x c e e d i n g l y luminous s t e l l a r or s e m i - s t e l l a r n u c l e u s . . . " S e y f e r t measured 15 l i n e s i n NGC 1068, i n c l u d i n g s e v e r a l f o r b i d d e n l i n e s , and the Balmer l i n e s of Hydrogen, and d e r i v e d widths f o r the l i n e s ranging from 2400 km/s (He I I , X4686) to 3600 km/s (H l i n e s ) . The next study done on NGC 1068 was t h a t of Burbidge, Eurbidge and Prendergast (1959) who derived the r o t a t i o n curve to about 25" from the c e n t e r , based on s p e c t r a from r e g i o n s near the nucleus, d e r i v e d a mass d i s t r i b u t i o n c o n s i s t i n g of a d i s k plus a unifrom spheriod, the l a t t e r w i t h i n the i n n e r 20" of the g a l a x y , and estimated the t o t a l mass w i t h i n t h i s r e g i o n to be about 2.6x10»o H©. By s t u d y i n g the e f f e c t on the shape of the r o t a t i o n curve of a l a r g e c e n t r a l mass, they placed c o n s t r a i n t s l i m i t i n g the n u c l e a r mass t o about 3x10? M 0. In the past 15 years NGC 1068 has been e x t e n s i v e l y s t u d i e d at a l l wavelengths. A review of the l i t e r a t u r e 53 p r e s e n t e d s i n c e 1965 i s most i n f o r m a t i v e i f , as w i l l be done h e r e , t h e i n v e s t i g a t i o n s a r e d i v i d e d i n t o the f o l l o w i n g c a t e g o r i e s : s p e c t r o s c o p i c s t u d i e s , p o l a r i z a t i o n , o p t i c a l p hotometry, IE o b s e r v a t i o n s , r a d i o , and DV and X-ray. (a) S p e c t r o s c o p i c O b s e r v a t i o n s D i b a i and P r o n i k (1965) s t u d i e d t h e spectrum of the n u c l e u s of NGC 1068, and d e r i v e d an e s t i m a t e f o r t h e e l e c t r o n d e n s i t y and t e m p e r a t u r e , as w e l l as e s t i m a t i n g t h e volume o f t h e e m i t t i n g gas. They determined a v a l u e of 20 p a r s e c s f o r t h e e f f e c t i v e r a d i u s of the e m i t t i n g r e g i o n and c o n c l u d e d , s i n c e t h e e m i t t i n g r e g i o n i s observed t o be of o r d e r 200 p a r s e c s , t h a t t h e gas i s not u n i f o r m l y d i s t r i b u t e d . O s t e r b r o c k and P a r k e r (1965) r e p o r t e d l i n e i n t e n s i t i e s f o r the H°( and j l l i f ] l i n e s t h a t were a l m o s t t w i c e t h o s e measured by S e y f e r t (1943)., and c a l c u l a t e d a very l a r g e Balmer decrement. They a l s o suggested t h a t t h e r e were d e n s i t y v a r i a t i o n s i n t h e n u c l e u s , i n agreement w i t h D i b a i and P r o n i k , by comparing the d e n s i t y d e r i v e d from the IK f l u x w i t h t h a t d e r i v e d from the f o r b i d d e n l i n e r a t i o s . I n d i s c u s s i n g p o s s i b l e e x c i t a t i o n mechanisms, they suggested t h a t t h e e m i s s i o n spectrum c o u l d a r i s e from c o l l i s i o n a l e x c i t a t i o n from the moving gas c l o u d s , o r from uv s y n c h r o t r o n r a d i a t i o n . 54 Walker (.1968) obtained s p e c t r a which r e s o l v e d the emission f e a t u r e s i n t o s e v e r a l components, from which he concluded t h a t the emission a r i s e s from at l e a s t four c l o u d s of diameters -200-350 parsecs, and masses of 10 6-10 7 Ms, so t h a t the emission r e g i o n i s l a r g e r than the n u c l e a r continuum source. Walker a l s o measured the r o t a t i o n curve f o r r e g i o n s o u t s i d e the n u c l e u s , which i n d i c a t e d both r o t a t i o n and expansion w i t h i n 25" from the c e n t e r , and c i r c u l a r motions f o r r >30". Wampler (1968 and 1971) determined t h a t t h e r e was s u b s t a n t i a l reddening i n the emission l i n e s , but not n e c e s s a r i l y i n the continuum, by c a l c u l a t i n g the r a t i o of [s if] )\4072 and )\10320, which t h e r e f o r e r e g u i r e d t h a t the e l e c t r o n d e n s i t y and temperature d e t e r m i n a t i o n s of e a r l i e r o bservers be m o d i f i e d . He suggested t h a t the reddening was due to dust i n the nucleus. However, the observed reddening from the \s if] l i n e s c o u l d not account f o r the very l a r g e Balmer decrement. In a l a t e r study, Koski (1978) observed the spectrum from 3700A to 6800A, and measured a Balmer decrement that c o u l d be explained using the amount of reddening d e r i v e d by Wampler. S o u f f r i n (1969) and A n d r i l l a t and S o u f f r i n (1971) determined that the observed i o n i z a t i o n i n the nucleus was probably due t o nonthermal r a d i a t i o n , Ey f i t t i n g the e g u i v a l e n t width of a b s o r p t i o n l i n e s i n the nucleus with those 55 c a l c u l a t e d f o r v a r i o u s s t e l l a r p o p u l a t i o n s and d i f f e r e n t amounts of n o n s t e l l a r continuum, they concluded t h a t the dominant s t a r type was K-M, and t h a t the continuum was not a p p r e c i a b l y reddened. Later ( A n d r i l l a t and C o l l i n - S o u f f r i n , 1975) they measured the spectrum from 7000A-11000A, and r e p o r t e d h i g h - i n t e n s i t y [~S III) )N\9069,9532 i n NGC 1068 and NGC 4151, but not i n other S e y f e r t s . They suggested t h i s was because these two g a l a x i e s had l e s s s t e l l a r c o n t r i b u t i o n than t h e other S e y f e r t s s t u d i e d . Anderson (1970) compared the f o r b i d d e n and permitted l i n e p r o f i l e s , and found they were e s s e n t i a l l y i n d i s t i n g u i s h a b l e f o r NGC 1068, i n c o n t r a s t to other S e y f e r t s , and a l s o confirmed a very strong Ca II a b s o r p t i o n f o r t h i s galaxy. He modeled the n u c l e a r r e g i o n to c o n s i s t of three components: a s t e l l a r component, nebulae producing the observed emission l i n e s , and a recombination continuum. The spectrum was s t u d i e d f u r t h e r by Khachikian and Weedman (1974), who c l a s s i f i e d NGC 1068 as a S e y f e r t type 2, that i s , with f o r b i d d e n l i n e s and Balmer l i n e s of the same width, by Martin (1974), and by S c h i l d (1972), who d e r i v e d an age e s t i m a t e f o r the galaxy by comparing the energy d i s t r i b u t i o n with t h a t of other s t e l l a r systems, assuming a s o l a r composition f o r the s t a r s . The d e r i v e d age i s of order 5.05x10 years. E i l e k et a l (1973) observed the blended H^, [N I i ] l i n e s 56 and compared t h e i r s p e c t r a , taken over three months, with t h a t of Osterbrock and Parker (1965). They deconvolved the blend and found t h a t the IK l i n e had v a r i e d i n i n t e n s i t y and width over the three month p e r i o d , from which they determined t h a t the s i z e of the e m i t t i n g r e g i o n was of order 10* 7 cm. In a l a t e r paper (Glaspey et a l , 1976) , the jjb III] l i n e was observed over about one year, and no v a r i a t i o n was r e p o r t e d . A l l o i n and Sareyan (1974) measured f l u x e s f o r the tij$, [o i f ] )\3726, and [b III] emission l i n e s , and the continuum, through narrow i n t e r f e r e n c e f i l t e r s , and used the data to determine the p h y s i c a l c o n d i t i o n s i n the n u c l e u s . T h e i r r e s u l t s concurred with A n d r i l l a t and C o l l i n - S o u f f r i n (1975) t h a t NGC 1068 had l e s s s t e l l a r c o n t r i b u t i o n i n the nucleus than normal g a l a x i e s . S h i e l d s and Oke (1975) r e p o r t e d a 40$ d e c l i n e i n the H* f l u x between 1965 and 1972. Based on the d e n s i t i e s d e r i v e d from the. js if] l i n e s and the [A ivj and jo III] l i n e s , they modeled the e m i t t i n g r e g i o n as c o n s i s t i n g of two zones: one with Ne~ 800 c m - 3 g i v i n g r i s e to the |j5 I l j l i n e s , and one with N e~2x10 s cm - 3 g i v i n g r i s e to the h i g h e r e x c i t a t i o n l i n e s . They a l s o suggested t h a t n i t r o g e n was overabundant i n NGC 1068 compared to s o l a r values, from an a n a l y s i s of the l i n e i n t e n s i t i e s . Yankulova (1975) used a power law c e n t r a l i o n i z i n g source and computed t h e o r e t i c a l emission l i n e i n t e n s i t i e s . He d e r i v e d 57 a diameter of ^ 1 4 parsecs f o r the e m i t t i n g r e g i o n . E i c h s t o n e and Morton (1975) measured the spectrum i n the r e g i o n 3880A-4120A. They c a l c u l a t e d a v e l o c i t y d i s p e r s i o n o f 150*50 km/s f o r the s t a r s i n the nucleus from measurements of the Fe I )\4046 a b s o r p t i o n l i n e . They d e r i v e d a mass o f 14x10 8 M© f o r the c e n t r a l r e g i o n using a n u c l e a r r a d i u s o f r "140 parsecs. Grandi (1978) measured [Fe Xi] X 7892 which he r e p o r t e d was s l i g h t l y b l u e s h i f t e d compared to the other emission l i n e s . He suggested t h i s i s due t o absorbing dust c o n f i n e d to a r e g i o n near the continuum source, so t h a t only those high i o n i z a t i o n i o n s expanding toward us c o n t r i b u t e t o the l i n e , whereas the dust does not extend out f a r enough t o obscure the low i o n i z a t i o n i o n s . Absolute spectrophotometry of the continuum of NGC 1068 has been pub l i s h e d by Walker (1968), f o r the wavelength range 3500A-4300A, S c h i l d (1972) f o r the range 3500A-6000A, A l l o i n and Sareyan (1974) f o r the range 3300A-6300A, S h i e l d s and Oke (1975) i n the range 3300A-11090A, Koski (1978) i n the range 3700A-6800A, and deBruyn and Sargent (1978) i n the range 3140A-10680A. .(b). P o l a r i z a t i o n . 58 P o l a r i z a t i o n of the o p t i c a l r a d i a t i o n from the nucleus o f NGC 1068 was f i r s t r e ported by Walker (1964), who measured 3% p o l a r i z a t i o n i n the yellow wavelength r e g i o n , and about 13% at u l t r a v i o l e t wavelengths. The p o l a r i z a t i o n was confirmed by E l v i u s and H a l l (1965), who measured the blue wavelength r e g i o n as w e l l , and noted t h a t the degree of p o l a r i z a t i o n decreased with i n c r e a s i n g wavelength. Dombrovskii and Hagen-Torn (1968) measured p o l a r i z a t i o n i n the V and B f i l t e r , and i n white l i g h t , f o r d i f f e r e n t aperture s i z e s . They again confirmed the c o r r e l a t i o n of p o l a r i z a t i o n with wavelength, and a l s o noted t h a t the p o l a r i z a t i o n i n c r e a s e d with decreasing aperture s i z e , i n d i c a t i n g t h a t the p o l a r i z e d l i g h t i s concentrated i n the nucleus. They d e r i v e d a value of 3% f o r the p o l a r i z a t i o n i n the nucleus, and suggested t h a t the p o l a r i z a t i o n was due to a high-freguency synchrotron component which had not been d e t e c t e d . In another paper (Dombrovskii et a l , 1971) they measured 1% p o l a r i z a t i o n i n the B band, and .1% i n the V and B bands. Visvanathan and Oke (1968) measured the p o l a r i z a t i o n i n U, B, V and fi f o r 3 aperture s i z e s , and found no v a r i a b i l i t y i n the p o l a r i z e d f l u x . They modeled the nucleus as c o n s i s t i n g of a nonthermal component causing the p o l a r i z a t i o n , and a thermal, s t e l l a r component. By assuming t h a t the p o l a r i z a t i o n i n the thermal component i s constant with wavelength, they 59 derived the energy d i s t r i b u t i o n curve for the nonthermal component, which resembled that of a QSO. Nandy and wolstencroft (1970) instead suggested that the po l a r i z a t i o n arose from scattering by a dense s h e l l of dust grains surrounding the nucleus. From t h i s model they were able to reproduce the previously calculated degree of p o l a r i z a t i o n , based on the observations (39.9% for a nucleus of diameter 1.5), and the position angle. Kruszewski (1971) reported an almost constant polarized flux for apertures larger than 7", and f i t t e d a power law '.3.X function, of the form Fj, = rvt/ , to the measured f l u x . His data was inconclusive i n determining whether the polarization had varied. However Babadzhanyants et a l (1972) stated that the degree of polarization had varied between 1.25Sf and .5% i n the B band. The polarization d i r e c t i o n did not change, so they concluded that the observed change was due to a brightness increase, with the additional radiation 9.5% polarized. They modeled the nucleus as having a f l a t power law spectrum with 8% p o l a r i z a t i o n , and another component with a steep spectrum, giving r i s e to the observed infrared excess. Because of the high degree of po l a r i z a t i o n , they suggested that r e l a t i v i s t i c p a r t i c l e s were being ejected from the nucleus i n cne d i r e c t i o n . The guestion of the source of the polarization was again considered by S i k u l i n et a l (1971) who reported c i r c u l a r 60 p o l a r i z a t i o n of about 1% i n the nucleus, which made a synchrotron source l e s s l i k e l y as a cause of the p o l a r i z a t i o n . Subsequently, s e v e r a l observers (Nordsieck, 1972, G e h r e l s , 1972, Kemp et a l , 1972, La n d s t r e e t and Angel, 1972) looked f o r c i r c u l a r p o l a r i z a t i o n i n NGC 1068, with n e g a t i v e r e s u l t s . However, i n 1976 Angel e t a l , using a more s e n s i t i v e d e t e c t o r , d i d observe c i r c u l a r p o l a r i z a t i o n . In a d d i t i o n , they measured the p o l a r i z a t i o n i n the emi s s i o n l i n e s . The permitted l i n e s appeared to have the same p o l a r i z a t i o n as the continuum, whereas the fo r b i d d e n l i n e s had no p o l a r i z a t i o n , except f o r [ o . I I l J , which was p o l a r i z e d at a d i f f e r e n t angle and to a l e s s e r degree than the permitted l i n e s . To account f o r these r e s u l t s , they modeled the nucleus as c o n s i s t i n g o f a continuum and Balmer emission source surrounded by a dust s h e l l , which i s i n t u r n surrounded by a r e g i o n of f o r b i d d e n l i n e emission. The most recent study i s by E l v i u s (1978) who found t h a t not only the nu c l e u s , but a l s o r e g i o n s o u t s i d e the nucleus are p o l a r i z e d . In p a r t i c u l a r , he detected a cloud northeast o f the nucleus, about 10" l o n g , with 48 p o l a r i z a t i o n , and p o s i t i o n angle 135°. He suggested t h a t the f a r i n f r a r e d r a d i a t i o n and CO molecules which have been detected i n NGC 1068 a r i s e from these c l o u d s . P o l a r i z a t i o n i n the i n f r a r e d was measured by Knacke and Capps (1974), who made o b s e r v a t i o n s a t 3.5^, 10.2/i, and 18.4/f. They s t a t e d t h a t the observed p o l a r i z a t i o n c ould be e x p l a i n e d 61 by nonthermal e m i s s i o n , i f , i n a d d i t i o n t o the observed 10/f IE s o u r c e , there uas a l s o a compact source. The data could a l s o be e x p l a i n e d as a r i s i n g from s c a t t e r i n g by g r a i n s , or by a combination of the two mechanisms. Eadio p o l a r i z a t i o n o b s e r v a t i o n s have been presented by Bologna et a l (1965) at 21 cm, Maltby and S e i e l s t a d (1966) a t 10.6 cm, Eerge and S e i e l s t a d (1967) at 18 cm, Strom (1973) at 49 cm, and ffardle and Sramek (1974) at 11.1 and 3.7 cm. In each case the p o l a r i z a t i o n . observed was l e s s than 1.535, and i n general did not c o r r e l a t e i n p o s i t i o n angle with the o p t i c a l and i n f r a r e d measurements. . (c) UBV Photometry P e t i t (1954) c a l c u l a t e d mn f o r 3 aperture s i z e s , ranging from 14 to 4 i 1 , based on measurements obtained using a p h o t o m u l t i p l i e r tube. Pacholcyzyk and Wisniewski (1967) measured OBVEIJHKL f l u x e s f o r NGC 1068 through a 15" diaphragm. T h e i r f l u x diagram showed t h a t NGC 1068 had a l a r g e excess a t s h o r t and long wavelengths i n the observed range. The r a d i a t i o n excess was shown to be s i m i l a r to t h a t o f 3C 273, t h e r e f o r e they suggested t h a t t h e r e was a g u a s a r - l i k e component i n the nucleus of the galaxy. Sandage (1967) published OBV photometry f o r 5 a p e r t u r e s , 62 ranging from 4l'9-20", and measured the t o t a l magnitude (that i s , the magnitude i n s i d e the Holmberg r a d i u s ) . He pointed out t h a t the c o l o r s became redder with i n c r e a s i n g a p e r t u r e s i z e , because the u n d e r l y i n g galaxy i s composed of l a t e type s t a r s . In comparison with other S e y f e r t s , h i s c o l o r diagram showed t h a t NGC 1068 had a redder n u c l e u s . De Vaucouleurs and de Vaucouleurs (1968) measured the n u c l e a r l u m i n o s i t y i n the B band as w e l l as p r o v i d i n g OBV magnitudes f o r s e v e r a l aperture s i z e s , and r e p o r t e d n e g a t i v e r e s u l t s i n s e a r c h i n g f o r v a r i a b i l i t y i n the f l u x , i n t h a t the s c a t t e r i n measurements by them and other observers i s l e s s than .1 mag. Using the a v a i l a b l e data they presented B-V and U-B c o l o r - a p e r t u r e r e l a t i o n s and the magnitude-aperture r e l a t i o n f o r the U and B bands. Photometry has a l s o been p u b l i s h e d by Walker (1968) f o r 6 ape r t u r e s from 11" to 280", Hodge (1968), who provided V i s o p h o t e s from a photographic p l a t e taken with a 48 i n c h t e l e s c o p e , Westerlund and Wall (1969), who suggested t h a t the very red c o l o r s c f the nucleus of NGC 1068 were due to dust i n t h a t r e g i o n , and Smith et a l (1975), who measured the nucleus as w e l l as other p o s i t i o n s i n the d i s k , and concluded t h a t the d i s k i s too blue f o r the galaxy's morphological type. Surveys f o r v a r i a b i l i t y i n the o p t i c a l continuum have been made i n 0, B and V by Barnes (1968) over a 6 month p e r i o d . Cannon et a l (1971), who measured photographic B 63 magnitudes on 8 p l a t e s taken over 18 months, L y u t y i (1973) over a t h r e e year p e r i o d , and Penston et a l (1974) over a one year p e r i o d . In each study the observed f l u c t u a t i o n was not s u f f i c i e n t l y above the photometric e r r o r s t o e s t a b l i s h the e x i s t e n c e of v a r i a b i l i t y . Penston e t a l placed a l i m i t of .05 mag rms on v a r i a t i o n s i n the U, B, and V f l u x . Zasov and L y u t y i (1973) suggested on the b a s i s of t h e i r survey t h a t S e y f e r t g a l a x i e s with " b l u e " n u c l e i v a r i e d , while those with "red" n u c l e i , l i k e NGC 1068, d i d not. In a l a t e r paper, however, L y u t y i (1977) i n d i c a t e d t h a t the o p t i c a l b r i g h t n e s s v a r i a t i o n s i n NGC 1068 were r e a l , and c o u l d be separated i n t o two components; one , c y c l i c , o c c u r i n g on a time s c a l e of a few y e a r s , and one with a v a r i a b i l i t y time s c a l e of tens of days. The amplitude of v a r i a t i o n was g r e a t e s t i n the 0 f i l t e r . He f u r t h e r suggested on the b a s i s o f s t u d i e s of s e v e r a l S e y f e r t g a l a x i e s , that the amplitude of v a r i a t i o n was c o r r e l a t e d with the a x i a l r a t i o of the galaxy, and t h a t the time s c a l e f o r v a r i a t i o n depended on the l u m i n o s i t y . L y u t y i ' s o b s e r v a t i o n s of H°< through a wedge i n t e r f e r e n c e f i l t e r a l s o i n d i c a t e d v a r i a t i o n over a time s c a l e of 5-15 days r e p e a t i n g the f a s t component of the continuum v a r i a t i o n s , but with a l a g of about 15 days. He suggested t h a t the l a g was the time r e g u i r e d f o r the i o n i z a t i o n r a d i a t i o n t o t r a v e l from the c e n t r a l source to the edge of the IK-forming r e g i o n , and thus d e r i v e d a s i z e of 1 0 4 7 cm f o r the H«c r e g i o n . 64 jdJL I/B o b s e r v a t i o n s P a c h o l c y z y k and W i s n i e w s k i (1967) p r e s e n t e d the f i r s t I/R photometry f o r NGC 1068. T h e i r work was s u p p o r t e d by a s t u d y by Moroz and D i b a i (1968) who measured the f l u x a t 1.6// and 2.1^ through a 20" diaphragm. The c o l o r t h e y d e r i v e d from t h e s e o b s e r v a t i o n s was t h e same, to w i t h i n t h e e r r o r s o f measurement, as t h a t of 3C 273, and they c o n f i r m e d t h e I/E e x c e s s r e p o r t e d by P a c h o l c y z y k and W i s n i e s k i a t 2my/m I n two papers (Low and Kleinmann, 1968, and Kleinmann and Low,1970) the o b s e r v e r s r e p o r t e d s t u d i e s of t h e c o n t i n u o u s energy d i s t r i b u t i o n of NGC 1068 from Vf t o 25/f, which t h e y f i t t o a power law of the form Styyv . They a l s o p r e s e n t e d e v i d e n c e f o r v a r i a b i l i t y i n t h e i n f r a r e d f l u x . P a c h o l c y z y k and Weymann (1968) r e p o r t e d e v i d e n c e o f v a r i a t i o n i n t h e f l u x a t 2.2/^. F u r t h e r m o n i t o r i n g ( P a c h o l c y z y k , 1970) c o n f i r m e d t h e v a r i a t i o n , w i t h a t i m e s c a l e o f a few d a y s , which p l a c e d a l i m i t o f about 1 0 l s cm f o r t h e s i z e of t h e i n f r a r e d e m i t t i n g r e g i o n . He c o n c l u d e d t h a t the model of Eees e t a l (1969) which suggested t h a t t h e i n f r a r e d r a d i a t i o n of NGC 1068 c o u l d be e x p l a i n e d i f t h e c e n t r a l , compact s o u r c e were surrounded by a d u s t c l o u d , was not v a l i d because i t r e g u i r e d t h a t the 2.2/c e m i t t i n g r e g i o n be a d i s t a n c e of 10* 8 cm from the c e n t r a l s o u r c e . I n s t e a d , he p r e s e n t e d a model o f a s y n c h r o t r o n s o u r c e i n which t h e f i e l d d e c reases outward. 65 Neugebauer e t a l (1971) measured t h e f l u x a t 1.6^, 2.2/Y,and 1Q/i, and observed a dependence on a p e r t u r e s i z e a t t h e s m a l l e r w a v e l e n g t h s , i n d i c a t i n g and extended s i z e f o r the source o f t h a t r a d i a t i o n , but no a p e r t u r e dependence f o r the 1 0 A f l u x , which suggested t h a t t h i s r a d i a t i o n a rose from a p o i n t s o u r c e . B e c k l i n e t a l (1973) d e r i v e d a s i z e of 1" f o r t h e 10x s o u r c e , by c o n v o l v i n g a b e s t f i t model s o u r c e d i s t r i b u t i o n w i t h t h e response f u n c t i o n , and comparing t h e r e s u l t t o t h e o b s e r v a t i o n s . At t h e d i s t a n c e o f NGC 1068, ( 11 Mpc) t h i s c o r r e s p o n d s t o a s i z e of 100 pc f o r the 10_M s o u r c e . Low and B i e k e (1971, and B i e k e and Low, 1972) p r e s e n t e d e v i d e n c e f o r v a r i a b i l i t y of the 10// f l u x based on o b s e r v a t i o n s made over 3 y e a r s . The amount o f v a r i a t i o n was about .5%. They a l s o r e p o r t e d an apparent d e c l i n e i n the 3.5// and 5/f f l u x . However, S t e i n e t a l (1974), m o n i t o r i n g t h e f l u x a t 11/^ o v e r t h e same ti m e i n t e r v a l , observed no v a r i a t i o n . They found t h a t t h e s p e c t r a l energy d i s t r i b u t i o n between 8/f and 13*f c o u l d be f i t t e d w i t h a power law o f t h e form F ( V Y . V a r i a b i l i t y was a l s o i n v e s t i g a t e d by Fenston e t a l (1974) who observed NGC 1068 a t 1.6/f, 2.2/1, and 3.4/f. They d i d not d e t e c t v a r i a b i l i t y a t t h e s e wavelengths. They p o i n t e d out t h a t NGC 1068 had a much s t e e p e r I/B spectrum, than t y p e 1 S e y f e r t s . B i e k e (1978) made o b s e r v a t i o n s from 1.25 -10.6/{ and found no b r i g h t n e s s changes l a r g e r than 20X-Low and Aumann (1970) measured t h e spectrum from 50-300/Y. 66 T h e i r r e s u l t s i n d i c a t e d a peak i n the spectrum at around 70yy, and a steep d e c l i n e at longer wavelengths. Subseguent o b s e r v a t i o n s by Harper et a l (1972) and Harper and Low (1973) f a i l e d t o confirm t h i s d e t e c t i o n . However, a i r b o r n e photometry by T e l e s c o e t a l (1976) from 28-320W, i n d i c a t e d a turnover i n the spectrum a t 100/f, i n support of the r e s u l t s of Low and Aumann. The o b s e r v a t i o n s of Jameson e t a l (1974a and 1974b) from 2.2-27/C i n d i c a t e d a peak i n the spectrum a t 1&W. They suggested, based on the s i m i l a r i t y of the spectrum of NGC 1068 to t h a t of a p l a n e t a r y nebula, t h a t dust r e r a d i a t i o n was the most l i k e l y source of the I/E r a d i a t i o n . The peak they reported was corroborated by Simon and Dyck (1975), from o b s e r v a t i o n s at 28/K and 33/(, but not observed by Eieke and Low (1975),. The l a t t e r o bservers measured the r a d i a t i o n from 2.2-40/1 and detected a dip i n the continuum at 10/f, which they t e n t a t i v e l y i d e n t i f i e d as a weak s i l i c a t e f e a t u r e . T h i s was confirmed by the spectrophotometry of Kleinmann e t a l (1976) and f u r t h e r s t u d i e d by Lebofsky et a l (1978), using narrow band photometry. The l a t t e r o b s e r v e r s a l s o r e p o r t e d a s i l i c a t e emission f e a t u r e at 19/f, and f u r t h e r determined t h a t the str e n g t h of these f e a t u r e s i n d i c a t e d a higher e x c i t a t i o n than t h a t determined from o p t i c a l s p e c t r a . Jones et a l (1977) computed models to f i t the s p e c t r a l energy d i s t r i b u t i o n from 3500A-300/C. T h e i r work i n d i c a t e d t h a t 67 t h e observed r a d i a t i o n c o u l d be modeled as a r i s i n g from a n u c l e u s surrounded by a s p h e r i c a l dust c l o u d of v i s u a l o p t i c a l depth ~10. They were unable t o f i t the r a d i a t i o n longward o f )r30/f , and suggested t h a t t h i s r a d i a t i o n might be e m i t t e d by r e g i o n s o u t s i d e the n u c l e u s . The d u s t g r a i n s used i n t h e i r model were a m i x t u r e of s i l i c a t e and g r a p h i t e . Eecent work has support e d the model of Jones e t a l . L e b o f s k y e t a l (1978) found t h a t a power law s o u r c e w i t h an o b s c u r i n g c l o u d f i t t h e i r o b s e r v a t i o n s o f the p o l a r i z a t i o n a t T h e i r r e s u l t s i n d i c a t e d a d i f f e r e n t p o l a r i z a t i o n a n g l e f o r the 3.4/f p o l a r i z a t i o n than t h a t g i v e n by Knacke and Capps (1974). I n a d d i t i o n , they found t h a t t h e p o l a r i z a t i o n d ecreased w i t h i n c r e a s i n g a p e r t u r e s i z e , i n agreement w i t h t h e o p t i c a l o b s e r v a t i o n s . They c o n c l u d e d t h a t t h e n u c l e u s was an i n t r i n s i c a l l y p o l a r i z e d source and suggested f u r t h e r t h a t t h e n u c l e u s may o n l y be o b s e r v a b l e i n t h e 1-5W wavelength r a n g e , because a t s h o r t e r wavelengths the s t a r s s u r r o u n d i n g the n u c l e u s c o n t r i b u t e s i g n i f i c a n t l y , and a t l o n g e r wavelengths t h e dust e m i s s i o n becomes i m p o r t a n t . Thompson e t a l (1978) o b s e r v e d t h e spectrum of NGC 1068 a t 2.2/y[ and determined t h a t the continuum had a power law dependence on f r e g u e n c y , w i t h s p e c t r a l i n d e x <=-2.6, i n agreement w i t h e a r l i e r p h o t o m e t r i c r e s u l t s . They observed t h e m o l e c u l a r hydrogen l i n e s a t X=2.04A/ and X=2. 12/f, which t h e y suggested were e x c i t e d by shock f r o n t s produced by r a d i a t i o n 68 from the nucleus impinging on dust clouds o u t s i d e the nucleus. C a r l s o n and F o l t z (1979) considered the p o s s i b i l i t y o f molecular hydrogen formation i n a r e g i o n about 50 pc from the continuum source, using the r a d i a t i o n f i e l d determined by S h i e l d s and Oke (1975). T h e i r r e s u l t s i n d i c a t e d t h a t p h o t o i o n i z a t i o n of carbon i n the cloud s would absorb almost a l l photons with 100A, and t h a t i n the presence o f dust, v i r t u a l l y a l l the hydrogen i n the clouds would be molecular. fe) Badio o b s e r v a t i o n s NGC 1068 was l i s t e d i n the 3C c a t a l o g as a r a d i o galaxy, designated 3C 271. Howard and Haran (1964) l i s t the o b s e r v a t i o n s of NGC 1068 made to 1964 from 10 cm t o 800 cm. The next study i n t h i s wavelength r e g i o n was by Cohen et a l (1967), who det e c t e d a r a d i o source of diameter l e s s than 0»3 from i n t e r p l a n e t a r y s c i n t i l l a t i o n measurements a t 49, 70, and 154 cm. Bash (1968) made i n t e r f e r o m e t r i c o b s e r v a t i o n s at 11.1 cm. He was a b l e t o account f o r the observed i n t e r f e r e n c e f r i n g e s by modeling the source at th a t wavelength as c o n s i s t i n g of two components, a core of s i z e l e s s than 1."5 and a halo of s i z e about 112 5.. Kellermann et a l (1970) used a two-element i n t e r f e r o m e t e r with a 10000 km b a s e l i n e t o measure the f l u x at 69 13 cm. T h e i r f r i n g e amplitudes i n d i c a t e d t h a t the source c o n t a i n s s t r u c t u r e on a s c a l e of i'001 but they were unable to model the source due to the complexity of the r a d i o spectrum. Fomalont and Moffet (1971) made i n t e r f e r o m e t r i c measurements at 21 cm along a north-south and an east-west b a s e l i n e . The diameter of the source along the north-south b a s e l i n e was determined to be l e s s than 21", while that along the east-west b a s e l i n e was l e s s than 15" . A l l e n e t a l (1971) detected H I i n emission i n NGC 1068 from o b s e r v a t i o n s at 21 cm. T h i s o b s e r v a t i o n was confirmed by l e w i s (1972), by Eoberts and Steigerwald (1977), and by Heckman et a l (1978). The l a t t e r o bservers noted an unusually low r a t i o of hydrogen mass to t o t a l l u m i n o s i t y f o r NGC 1068 compared to other g a l a x i e s of the same morphological type. They suggested t h a t the missing mass could be i n the form of molecular hydrogen i n the c e n t e r , a suggestion which i s supported by the i n f r a r e d o b s e r v a t i o n s of Thompson et a l (1978). Heckman et a l a l s o presented a map of H I i n NGC 1068 i n d i c a t i n g t h a t most of the H I may be a s s o c i a t e d with the outer r i n g v i s i b l e i n photographs i n the Hubble a t l a s (Sandage, 1961), and t h a t the s c a l e length of the H I d i s t r i b u t i o n was l a r g e r than the o p t i c a l s i z e of the galaxy. De Bruyn and Wilson (1976) presented continuum o b s e r v a t i o n s at 21.2 cm, from which they c a l c u l a t e d a s p e c t r a l index of °<=-0. 75. 70 Observations a t s m a l l e r wavelengths have been made by K u r i l ' c h i k et a l (1960) at 3-5 cm, S t u l l (1971) at 3.75 cm, Brandie and B r i d l e (1974) a t 3.8 cm and 1.4 cm, de Bruyn and W i l l i s (1974) a t 6 cm, and McCutcheon and Gregory (1978) at 1.35 and 2.85 cm. The o b s e r v a t i o n s of de Bruyn and W i l l i s confirmed the two component model of Bash (1968) i n t h a t t h e i r o b s e r v a t i o n s at high r e s o l u t i o n detected a p o i n t source and an asymmetric source extending t o about 10" north of the nucleus. They a l s o noted a d i s c r e t e source about 19" east of the c e n t e r , which c o i n c i d e s with a b r i g h t knot i n the o p t i c a l image. Brandie and B r i d l e (1974) reported no evidence f o r v a r i a t i o n of NGC 1068 a f t e r monitoring the f l u x f o r over 4 years. However, the o b s e r v a t i o n s of McCutcheon and Gregory (1978) over a 6 month p e r i o d i n d i c a t e d v a r i a b i l i t y at 2.8 cm. Millimeter-wave o b s e r v a t i o n s were f i r s t r e p o r t e d by Schorn e t a l (1968), who detected NGC 1068 at 3.4 mm and reported no evidence f o r v a r i a b i l i t y from o b s e r v a t i o n s over a 3 month p e r i o d . E p s t e i n and Fogarty (1968) noted a decrease i n the 3 mm f l u x i n o b s e r v a t i o n s taken over one year. F u r t h e r s t u d i e s (Fogarty e t a l , 1971, 1974) over 7 y e a r s , i n d i c a t e d t h r e e p e r i o d s during which the 3 mm f l u x was detected at l e v e l s s i g n i f i c a n t l y higher than the expected f l u x , estimated by e x t r a p o l a t i n g the energy d i s t r i b u t i o n curve at l o n g e r wavelengths. Kellerman and P a u l i n y - T o t h (1971) reported no 71 d e t e c t i o n of NGC 1068 a t 3 mm, as expected from c o n s i d e r a t i o n of the e x t r a p o l a t e d f l u x and the s e n s i t i v i t y l i m i t of the d e t e c t o r s at t h i s wavelength. They a l s o made o b s e r v a t i o n s a t 9,. 5 mm, and presented the continuous energy d i s t r i b u t i o n curve from i n f r a r e d wavelengths t o 75 cm. The I/B o b s e r v a t i o n s i n d i c a t e a steep d e c l i n e i n the spectrum a t \>*\00/{ but the o b s e r v a t i o n s of Kellerman et a l d i d not d e t e c t an upturn i n the r a d i o spectrum r e g u i r e d t o f i t the i n f r a r e d and r a d i o o b s e r v a t i o n s together. They f u r t h e r r e p o r t e d t h a t no change g r e a t e r than a few percent had been observed i n the spectrum at X> 2 cm over 2 years of o b s e r v a t i o n . Most r e c e n t l y , E l i a s et a l (1978) e s t a b l i s h e d an upper l i m i t of .6x10 - 2 * W m - 2 H Z - » f o r the f l u x at 1 mm. They a l s o measured the spectrum at 9.5mm, and repor t e d no d e t e c t i o n f o r the 3.4 mm f l u x . They p u b l i s h e d a s p e c t r a l energy d i s t r i b u t i o n curve f o r the 100X -10 cm range, which they noted could most e a s i l y be ex p l a i n e d as a r i s i n g from a thermal source. Subseguently, J u r a (1978) r e p o r t e d a marginal d e t e c t i o n f o r the 3.4 mm f l u x , again suggesting the p o s s i b i l i t y o f v a r i a t i o n of the f l u x at t h i s wavelength. Submillimeter o b s e r v a t i o n s were made by Hildebrand et a l (1977) from 390-1 lOOyY. T h e i r r e s u l t s i n d i c a t e d t h a t the spectrum f a l l s o f f s t e e p l y longward of 100/f, i n support of the r e s u l t s of T e l e s c o et a l (1976). They determined t h a t about 98% of the power r a d i a t e d from NGC 1068 i s from the 2 -1000/^ 72 wavelength r e g i o n , and t h a t t h e spectrum was b e s t modeled as a r i s i n g from an o p t i c a l l y t h i n dust c l o u d o f s i z e a t l e a s t 5". (f) H i^h enera_y o b s e r v a t i o n s K e l l o g g e t a l (1971) and Olmer and Murray (1976) r e p o r t e d no d e t e c t i o n i n a t t e m p t s t o observe X-ray e m i s s i o n from NGC 1068 u s i n g t h e OHUEU s a t e l l i t e . E l v i s et a l (1978) r e p o r t e d a p o s s i b l e d e t e c t i o n (4^r l e v e l ) of X-ray e m i s s i o n , u s i n g t h e A r i e l IV Sky Survey I n s t r u m e n t , i n the range 10-50 kev. U l t r a v i o l e t s p e c t r a o f NGC 1068 a t low d i s p e r s i o n , o v er t h e wavelength range 150-3200 was o b t a i n e d by Boksenberg e t a l (1978) u s i n g the IUE s a t e l l i t e . They p r e s e n t e d continuum f l u x e s f o r t h i s wavelength range from which t h e y d e r i v e d a power-law spectrum w i t h s p e c t r a l i n d e x ~ 1.8, u n c o r r e c t e d f o r r e d d e n i n g . U s i n g the r e d d e n i n g c o r r e c t i o n d e r i v e d from t h e jjS i f ] l i n e s , t h e y found t h a t the r e s u l t i n g UV spectrum was n o t a power law. They t h e r e f o r e suggested t h a t t h e continuum r e d d e n i n g i s much s m a l l e r than t h a t i n the e m i s s i o n l i n e s , and t h a t the t r u e s p e c t r a l i n d e x a f t e r r e d d e n i n g c o r r e c t i o n i s 7v<1.4. They a l s o d e r i v e a N/O r a t i o from t h e e m i s s i o n l i n e i n t e n s i t i e s which i s about s i x t i m e s the s o l a r r a t i o , c o r r o b o r a t i n g t h e r e s u l t s of S h i e l d s and Oke (1975). 73 I t i s useful to summarize the observational studies i n terms of a d i s c r i p t i o n of the inner 500 parsecs of the galaxy. In t h i s region there are several clouds of gas which give r i s e to the emission l i n e s . There are two types of clouds, probably interspersed, with d i f f e r e n t densities and temperatures..These clouds f i l l about .001 of the t o t a l volume of the emitting region. Within the inner 100 parsecs there i s an o p t i c a l l y thick dust cloud. In t h i s region there are cold, dense clouds containing molecular hydrogen, which i s shielded from the i o n i z a t i o n radiation by dust and by photoicnization of high energy photons by carbon in the clouds. The c e n t r a l continuum source of NGC 1068 i s nonthermal. Throughout the entire region there i s a s t e l l a r component as well, which probably dominates the .continuum radiation at v i s u a l or shorter wavelengths. The infrared radiation appears tc ari s e from reradiation by dust i n the central regions. The radio radiation includes a nonthermal compact component in the center, coincident with the o p t i c a l center, and an extended component. The observational elements of NGC 1068 are given i n Table 8. 7 4 Table 8 Elements Of NGC 1068 B.A. (1950) Dec (1950) 1, b L, B Type Velocity Apparent magnitude Color (B-V) Mean axis r a t i o Face-on diameter Corrected velocity 2"40ri -0° 14' 172^09, 51.*94 304:9, -25:8 (B) SA (rs) b •1080 km/s 9.7 0.66 0.80 4l9 +1094 km/s 2. Photometric C a l i b r a t i o n The photometric c a l i b r a t i o n for the V image of NGC 1068 was achieved through comparing simulated aperture i n t e n s i t i e s with published photometry. The p o s s i b i l i t y of variations i n the nuclear brightness of t h i s galaxy has been investigated by a number of observers, as discussed in the previous section, but with no conclusive r e s u l t s . However, an examination of the published photometry (Figure 19) shows a good deal of scatter, larger than the formal uncertainty estimated i n the 7 5 o b s e r v a t i o n s , l y u t y i (1977) c o n s i d e r s the s c a t t e r to be a r e s u l t of v a r i a b i l i t y of the nucleus, as d i s c u s s e d i n s e c t i o n 1. However, Penston et a l (1974) f i n d no evidence f o r v a r i a b i l b i t y based on the f a c t t h a t the rms s c a t t e r of t h e i r o b s e r v a t i o n s through the same ape r t u r e over a 2.year p e r i o d i s no g r e a t e r than the rms e r r o r i n the published photometry. The d i f f i c u l t y with t h i s i s t h a t i f the nucleus i s v a r i a b l e , e s p e c i a l l y on the r a p i d time s c a l e suggested by L y u t y i , t h i s would be a source of the rms s c a t t e r i n the p u b l i s h e d magnitudes. T h e r e f o r e , i n attempting to c a l i b r a t e the CCD image, there was c o n s i d e r a b l e d i f f e r e n c e i n the c a l i b r a t i o n constant V-v obtained from the published aperture photometry. In a d d i t i o n , f o r any one set of published photometry, the c a l i b r a t i o n of the CCD data tended to agree f o r l a r g e r a p e r t u r e s and be d i s c r e p a n t at s m a l l e r a p e r t u r e s (see Table 9) the B'V c o l o r s (Figure 20a) showed no s y s t e m a t i c trend with aperture s i z e . However, the simulated photometry of the CCD data shows a v-r c o l o r g r a d i e n t , as can be seen i n F i g u r e 20b. In attempting to c a l i b r a t e the CCD data with an expression of the form V = v / + "< + yJcV - r J (7) where V denotes the standard V magnitude, and v and r the i n s t r u m e n t a l magnitudes, the values obtained by l e a s t - s g u a r e s f i t t i n g were ^=25.47,^?=-.7692, with an e r r o r (sum of sguares) 76 c f .0946. Because, as noted e a r l i e r , the c a l i b r a t i o n i s more d i s c r e p a n t a t s m a l l e r a p e r t u r e s , which would be expected i f the nucleus were v a r i a b l e , and because there i s c o n t r o v e r s y on the guestion of v a r i a b i l i t y of the nucleus at o p t i c a l wavelengths, i t i s necessary t o c o n s i d e r the e f f e c t of v a r i a b i l i t y on the c a l i b r a t i o n , as was done f o r NGC 1566. A c c o r d i n g l y , the photometry was c a l i b r a t e d by comparing the l u m i n o s i t y i n s i d e s u c c e s s i v e a n n u l i , with i n n e r diameter l a r g e enough to exclude the n u c l e a r r e g i o n , measured by de Vaucouleurs (1968) as 9"x7'. T h i s c a l i b r a t i o n r e s u l t e d i n a mean V-v of 24.97, with C~=. 037. Thus the assumption of a v a r i a b l e nucleus allowed a b e t t e r f i t t o the p u b l i s h e d photometry. However, the v-r c o l o r g r a d i e n t must a f f e c t the c a l i b r a t i o n as w e l l , so the adopted c a l i b r a t i o n took account of both e f f e c t s . The i n s t r u m e n t a l magnitude i n s i d e each annulus f o r the CCD data was determined, along with the v^-r c o l o r i n t h a t annulus, and these were compared through Eguation 7 to the V magnitude d e r i v e d from the p u b l i s h e d photometry. The r e s u l t s of the l e a s t sguares f i t t i n g are given i n Table 9. Eeference 1 i s the data of Westerlund and Wall (1968), Reference 2 i s that of Walker (1968), Eeference 3 i s the data of de Vaucouleurs and de Vaucouleurs (1968), Reference 4 i s the data of Smith e t a l (1972), and Reference 5 i s t h a t of Penston et a l (1974). The 24" aperture o f t h i s 77 l a t t e r d a t a was not used i n t h e c a l i b r a t i o n , because i t was markedly d i s c r e p a n t i n comparison w i t h the o t h e r measurements. F o r the o t h e r e x i s t i n g photometry, t h e r e were not enough a p e r t u r e s i z e s l a r g e r t h a n 9" t o make comparison w i t h the CCD data u s e f u l . Two measurements of E magnitudes have been p u b l i s h e d ( P a c h o l c y z y k and W i s n i e w s k i , 1967, 0 , D e l l e t a l , 1978). However, s i n c e each o b s e r v a t i o n i n c l u d e d o n l y one a p e r t u r e s i z e , i t i s not p o s s i b l e t o c a l i b r a t e t h e CCD E image d i r e c t l y from t h e p u b l i s h e d photometry, due t o t h e app a r e n t v a r i a b i l i t y o f the n u c l e u s . T h e r e f o r e , a rough c a l i b r a t i o n o f t h e B image was d e r i v e d by making t h e assumption t h a t t h e V-B c o l o r does not change w h i l e the n u c l e u s v a r i e s . There i s some j u s t i f i c a t i o n f o r t h i s i n the da t a of Penston e t a l (1974), who i n d i c a t e l i t t l e change i n c o l o r w i t h b r i g h t n e s s v a r i a t i o n s f o r t h e S e y f e r t g a l a x i e s they s t u d i e d . P a c h o l c y z y k and W i s n i e w s k i g i v e V-E=.747 f o r a 15" a p e r t u r e , and O ' D e l l e t a l g i v e V-B=.75 f o r an 18" a p e r t u r e . A c c o r d i n g t o t h e c a l i b r a t i o n g i v e n i n Ta b l e 9, the CCD V magnitude f o r t h e 15" a p e r t u r e i s 11.11, u s i n g the measured i n s t r u m e n t a l v - r c o l o r of .92. F o r V-E=.747, the s t a n d a r d B magnitude f o r the CCD image i s 10.36. The c o r r e s p o n d i n g i n s t r u m e n t a l r magnitude i s -14.78. For the 18" a p e r t u r e , the i n s t r u m e n t a l v magnitude i s -14.06, t h e r magnitude i s -14.95, and t h e c o r r e s p o n d i n g V magnitude, from t h e c a l i b r a t i o n g i v e n 78 T a b l e 9 P h o t o m e t r i c C a l i b r a t i o n Of The V Image Of NGC 1068 Ap diam V Bef CCD v v^-r Annulus V CCD v V - r 12" 11.05 1 -13.59 .97 12" -20" 11.66 -13.22 .73 20" 10.56 1 -14. 18 .87 12"-40" 10. 55 -14.37 .6/ 40" 10.02 1 -14.80 .74 11" 11.03 2 -13.49 .94 11-17 11.97 -12.92 .71 17" 10.65 2 -14. .90 11"-28" 10.94 -13.97 j .71 28" 10. 23 2 -14.51 .83 i e : 2 10.8 3 -13.94 .91 16"-3i:'5 11.27 -13.77 .7k 31.'5 10.26 3 -14.61 .81 33" 10.22 3 -14.65 .81 . u 16-33" 11.17 -13.85 .61 79 Ap diam V Bef CCD V v - r Annulus V CCD v v-r 17" 10.94 4 - -14 . 9 26" 10.53 4 -14 .44 .85 17" -26 ' 11.74 - 1 3 . 2 5 • V 34" 10.3 4 -14 .68 .79 17"-34" 11.18 ^13.84 .67 I 15" 10.82 5 - 13 .85 .92 I | 24" 10.54 5 - 14 .36 .86 15"-24" 12. 15 - 1 3 . 3 I . 1 1 ' 1 1 30" 10.25 5 -14 .57 - .82 j 15"-30" 11.22 ^13.78 . 7 / 45" 10.01 5 - 1 4 . 8 8 ,.68 15 "-45" 10.71 - 1 4 . 3 5 .4* C a l i b r a t i o n : V=v+25.09-. 14064 (v-r) •30 ?~5 If /a. m. • * A I.O II I-i- l-J <-f IT IS I.J J.O toe. fareitrLiKe Ot/tHereK.) Figure 1?: V magnitude-aperture r e l a t i o n f o r NGC 1068, derived from the published photometry. Aperture diameters are i n arcseconds. The values determined by the various observers may be distinguished using the following key: •=Walker (1968) o=Westerlund and Wall (1968) •=de Vaucouleurs and de Vaucouleurs (1968) *=Smith et a l (1972) A=Penston et a l (1974) .7 - T .1 i.o 1.1 ri. 7J 7* 7*, Ti 71 Ti Ti LOG. (fiPeATUHE Dm/IE f£«) Figure 20: (a) v - r color-aperture r e l a t i o n f o r NGC 1068, obtained from the CCD observations. Aperture diameter i s i n arcseconds. (b) (B-V) color-aperture r e l a t i o n for NGC 1068. The points are from the published photometry l i s t e d i n Figure 19. 82 i n Table 9, i s 10.9, which i m p l i e s E=10.15 from the measured V-B of .75. Then from the 15" a p e r t u r e , B-r=25.14, and from the 18" a p e r t u r e , B-r=25.1, so the adopted c a l i b r a t i o n i s For the CCD o b s e r v a t i o n s , the e r r o r s i n the photometry f o r the outermost simulated a p e r t u r e s are +.04 mag f o r the V image, and t.01 mag f o r the B image. The u n c e r t a i n t y i n the c a l i b r a t i o n f o r the V image i s of the same order as the e r r o r i n the CCD V photometry. This i s s u b s t a n t i a l l y b e t t e r than the +.14 mag s c a t t e r i n the p u b l i s h e d photometry. The p u b l i s h e d photometry i s of course a l s o s u b j e c t t o other sources of e r r o r which might a l s o e x p l a i n the discrepancy i n the o b s e r v a t i o n s , p a r t i c u l a r l y the d i f f i c u l t y of c e n t e r i n g the aperture on the b r i g h t e s t p a r t of the image, which can be very important i n the photometry of S e y f e r t g a l a x i e s , s i n c e the l i g h t i s so concentrated toward the c e n t e r . However, the arguments p r e v i o u s l y presented i n t h i s s e c t i o n tend to support the p o s s i b i l i t y of v a r i a b i l i t y of the nucleus. In any case, s i n c e t h e g u e s t i c n of v a r i a b i l i t y i s not r e s o l v e d , the best c a l i - b r a t i o n i s one which excludes the c e n t r a l r e g i o n s of the galaxy. The discrepancy i n the p u b l i s h e d photometry can be s i g n i f i c a n t i f the photometry i s used to d e r i v e the l u m i n o s i t y p r o f i l e , i n the manner o u t l i n e d by de Vaucouleurs and deVaucouleurs (1974). T h i s p o i n t i s d i s c u s s e d f u r t h e r i n the Appendix. 83 F i g u r e 21 shows the COMTAL v-r image f o r NGC 1068. The reddening of the galaxy towards the c e n t r a l r e g i o n s i s e v i d e n t i n t h i s photograph. Of p a r t i c u l a r i n t e r e s t i s the f a c t t h a t the r e g i o n s of enhanced r e d i n t e n s i t y tend to l i e i n an e l o g a t e d r e g i o n along the major a x i s , P.A. 45 s. In the i n n e r r e g i o n s , however, the d i r e c t i o n of e l o n g a t i o n g r a d u a l l y t w i s t s toward P.A. 30". Other i n v e s t i g a t o r s (cf.,Burbidge e t a l , 1959, E e r t o l a , 1968) have noted an asymmetry i n the n u c l e a r r e g i o n s .of the galaxy along t h i s d i r e c t i o n . The s i g n i f i c a n c e of the f e a t u r e s mentioned here w i l l be d i s c u s s e d i n the next s e c t i o n . 3. Luminosity P r o f i l e s The contour map f o r the red image of NGC 1068 i s shown i n F i g u r e 22, and t h a t f o r the v i s u a l image i s shown i n F i g u r e 26. I t i s immediately apparent from these f i g u r e s t h a t the i n n e r r e g i o n of NGC 1068 i s asymmetric. The s p i r a l arms are o b v i o u s l y present to at l e a s t w i t h i n 14" from the center. In a d d i t i o n , the b r i g h t n e s s f a l l s o f f much f a s t e r on the southeast s i d e of the galaxy than on the opposite s i d e . For the v i s u a l image, i n a d d i t i o n to these asymmetries, the innermost contours a l s o c l e a r l y show the presence of o b s c u r a t i o n , as can be seen i n F i g u r e 26 and i n the COMTAL 84 p i c t u r e of tbe i n n e r r e g i o n s of the v i s u a l image, shown i n F i g u r e 27. For the red image, the contours o u t s i d e the i n n e r 5" of the image show a marked e l o n g a t i o n along the major a x i s of the galaxy. T h i s a l s o appears i n the COMTAL v-r image (Figure 21) as a r e g i o n of enhanced red e m i s s i c n . As a r e s u l t of the asymmetries descussed here, the l u m i n o s i t y p r o f i l e s of the red and v i s u a l images of NGC 1068 are g u i t e c o m p l i c a t e d , as can he seen i n F i g u r e s 23 and 28. These f i g u r e s show the l u m i n o s i t y p r o f i l e s d e r i v e d from t h r e e methods: the method d e s c r i b e d i n Chapter 1, and used i n Chapter 2 f o r NGC 1566, which uses the e g u i v a l e n t r a d i u s of the c o n t o u r s , the method d i s c u s s e d i n the Appendix, d e r i v e d from the simulated aperture photometry of the CCD images, and two p r o f i l e s d e r i v e d from p l o t t i n g the i n t e n s i t y along a l i n e running from the c e n t e r of the image a t P.A. 135° and a t P.A. 315". These l a s t two p r o f i l e s i l l u s t r a t e the e f f e c t of the r a p i d f a l l - o f f i n b r i g h t n e s s on the southeast s i d e of the galaxy. For NGC 1068 then, i n c o n t r a s t to NCG 1566, i t i s not p o s s i b l e t o approximately reproduce the observed image by g e n e r a t i n g a two-dimensional, axisymmetric model from the l u m i n o s i t y p r o f i l e s . Bather, the l u m i n o s i t y p r o f i l e r e p r e s e n t s the average p r o p e r t i e s of the s u r f a c e b r i g h t n e s s d i s t r i b u t i o n . For the a n a l y s i s of these images, the p r o f i l e s d e r i v e d from the contour maps w i l l be used, s i n c e t h i s type of p r o f i l e i s 85 independent of e l l i p t i c i t y . Beyond 11' (r y ,=1.82) the p r o f i l e i s a f f e c t e d by the change i n c o n t o u r shape due t o the s p i r a l arms. At r a d i i l e s s than t h i s , i t can be seen t h a t t h e p r o f i l e s are w e l l d e s c r i b e d by a deVaucouleurs r , / V law, o ver a t l e a s t 6''. As mentioned i n Chapter 1, an H°c image of NGC 1068 was a l s o o b t a i n e d w i t h t h e CCD. F i g u r e 31 i s a COMTAL p i c t u r e o f t h i s image. For t h i s p i c t u r e , t h e data was c o n v e r t e d t o a l o g r i t h m i c s c a l e i n o r d e r t o reduce the dynamic range so t h a t t h e o u t e r r e g i o n s c o u l d be seen. The change i n i n t e n s i t y from t h e o u t e r c o n t o u r t o the i n n e r c o n t o u r i s a f a c t o r o f about 90. O n f o r t u n a t e l y , t h e d a t a has a r a t h e r low s i g n a l - t o - n o i s e r a t i o (-8 f o r the o u t e r c o n t o u r ) . D e s p i t e t h i s , s e v e r a l f e a t u r e s of the H ^ - e m i t t i n g r e g i o n can be d i s c e r n e d . The most n o t i c e a b l e f e a t u r e i s t h a t t h e e m i s s i o n i s v e r y i n t e n s e i n the c e n t e r of the g a l a x y . F i g u r e 32 shows the c o n t o u r p l o t of t h i s image. The i n n e r c o n t o u r s agree i n shape and i n c l i n a t i o n w i t h the c e n t r a l c o n t o u r s of the red image. The H< and r e d images were g e o m e t r i c a l l y r e g i s t e r e d by s h i f t i n g t h e H°< image so t h a t t h e knot i n t h e s o u t h r e g i o n o f t h e g a l a x y , a l o n g the major a x i s , c o i n c i d e d w i t h the c o r r e s p o n d i n g f e a t u r e on the r e d image. From t h i s i t was found t h a t t h e c e n t r a l c o n t o u r s of t h e two images a l s o c o i n c i d e d . A second f e a t u r e t o be n o t e d i n t h e image i s t h a t t h e 86 e l o n g a t i o n along tbe major a x i s observed i n the red image a l s o seems t o be present here. T h i s f e a t u r e i s somewhat obscured along the southwest s i d e because there were s e v e r a l bad columns of p i x e l s i n t h a t r e g i o n of the CCD a r r a y , which accounts f o r the abrupt t r u n c a t i o n of the image on the south s i d e . A f i n a l f e a t u r e of the IK image i s t h a t i t i s asymmetric i n the o p p o s i t e sense to the red and v i s u a l image, i n t h a t the r e g i o n of these l a t t e r images where the b r i g h t n e s s f a l l s o f f most r a p i d l y (P.A, 135') i s a r e g i o n of enhanced IK e m i s s i o n . I f the b r i g h t n e s s f a l l - o f f i s due to the presence o f dust o b s c u r a t i o n i n the galaxy, t h i s would i n d i c a t e t h a t t h i s r e g i o n of NGC 1068 c o n t a i n s both gas and dust. , Since the red image of NGC 1068 i n c l u d e s a s i g n i f i c a n t c o n t r i b u t i o n from the E°< emission, i t was necessary to c o r r e c t f o r t h i s i n order to attempt to determine the n u c l e a r continuum component. The H* image was c a l i b r a t e d a c c ording t o the spectrophotometry of S h i e l d s and Oke (1975). The t o t a l f l u x i n the red bandpass through a 7" aperture d e r i v e d from t h e i r measurements i s approximately 1.5x10-*° ergs cm - 2 s _ 1 . The f l u x they measure f o r the HX emission i n t h a t aperture i s 2.11x10-** ergs cm- 2 s - 4 , so the t o t a l c o n t r i b u t i o n of the H<* f l u x t o the red l i g h t i s about 14SJ. The IK f l u x has been repor t e d t o be v a r i a b l e (cf E i l e k et a l , 1973, L y u t y i , 1977), but as noted by S h i e l d s and Oke and by Koski (1978) the t o t a l 87 s t r e n g t h of the IK* [N I l [ b l e n d agrees w i t h i n 5%, so t h a t t h e r e p o r t e d v a r i a t i o n may be due t o d i f f e r e n t t e c h n i g u e s f o r d e c o n v o l v i n g . t h e l i n e s . I n any c a s e , s i n c e the f i l t e r used f o r t h e CCD o b s e r v a t i o n s a l s o i n c l u d e s t h e [N i f ] l i n e s t h e e r r o r i n t r o d u c e d i n the c a l i b r a t i o n by p o s s i b l e v a r i a t i o n i s i g n o r a b l e i n a f i r s t a p p r o x i m a t i o n . A c c o r d i n g l y , the CCD H°< image was s c a l e d so t h a t the t o t a l i n t e n s i t y w i t h i n the i n n e r 7" d i a m e t e r r e g i o n of the HX image was 14% o f t h e t o t a l i n t e n s i t y i n s i d e t h e c o r r e s p o n d i n g r e g i o n o f the red image. The H°c image was t h e n s u b t r a c t e d from the r e d image. The c o n t o u r p l o t of the r e s u l t i n g image was very s i m i l a r t o the c o n t o u r map o f F i g u r e 22, except l e s s s t r o n g l y peaked i n the c e n t e r . The l u m i n o s i t y p r o f i l e d e r i v e d f o r t h e red-H* image i s shown i n F i g u r e 24, p l o t t e d a g a i n s t r , and t a b u l a t e d i n Table 10. Due t o t h e e f f e c t of t h e s p i r a l arms, and t o t h e l i m i t e d a r ea c o v e r e d by the CCD image, i t i s not p o s s i b l e t o d e t e r m i n e a d i s k p r o f i l e from the CCD o b s e r v a t i o n s . The Appendix d e s c r i b e s t h e d i s k p r o f i l e d e r i v e d from the p u b l i s h e d V photometry f o r NGC 1068. An attempt was made t o use t h i s d i s k p r o f i l e t o g e t h e r w i t h t h e CCD o b s e r v a t i o n s t o perform an i t e r a t i v e p rocedure t o d e r i v e t h e d i s k and b u l g e components f o r t h e V image, such as was used i n Chapter 2 f o r NGC 1566. However, no convergence was a c h i e v e d i n t h i s p r o c e s s . I n d e e d , s i n c e the p r o f i l e s d e r i v e d from the photometry assume a 88 c i r c u l a r l y symmetric s t r u c t u r e f o r the observed image of the galaxy, i t i s not c o n v i n c i n g that combining t h i s data with the p r o f i l e of F i g u r e 29 would be meaningful. An attempt was a l s o made to combine the p r o f i l e d e r i v e d from the pu b l i s h e d photometry with t h a t d e r i v e d from the simulated a p e r t u r e photometry of the CCD v i s u a l image. This attempt a l s o f a i l e d to produce a converging s o l u t i o n i n the i t e r a t i v e procedure. The d i s k model derived from the publi s h e d photometry f o r NGC 1068 would c o n t r i b u t e about 20% of the t o t a l l i g h t i n s i d e a r a d i u s of 18". By c o n t r a s t , the d i s k derived f o r NGC 1566 c o n t r i b u t e s more than 50% of the l i g h t i n s i d e i n s i d e t h i s r a d i u s . In the c e n t r a l r e g i o n s , the d i s k c o n t r i b u t i o n would be even s m a l l e r . And f o r the red image, the b r i g h t n e s s of the s t a r - l i k e nucleus, which i s mostly obscured i n the v i s u a l image, would f u r t h e r d i m i n i s h the r e l a t i v e c o n t r i b u t i o n o f the di s k component. Therefore the e r r o r i n t r o d u c e d i n i g n o r i n g t h i s component f o r r<11" i s not unacceptable. A f u r t h e r c o m p l i c a t i o n which arose i n a n a l y z i n g the l u m i n o s i t y p r o f i l e of NGC 1068 i s th a t there was no seeing p r o f i l e a v a i l a b l e f o r the n i g h t these o b s e r v a t i o n s were made. Therefore the bulge models were convolved with the se e i n g p r o f i l e s used i n Chapter 2 f o r NGC 1566 (Fig u r e s 8 and 16) . The NGC 1566 ob s e r v a t i o n s were made on the subseguent n i g h t t o the o b s e r v a t i o n s of NGC 1068. As a t e s t of the e f f e c t a change i n the se e i n g p r o f i l e would have on the c o n v o l u t i o n , the bulge 89 model f o r the red image was a l s o convolved with a pure Gaussian seeing p r o f i l e with cn=0.9. The r e s u l t i n g p r o f i l e f o r the convolved bulge d i f f e r e d by l e s s than 3.58 from t h a t determined by c o n v o l u t i o n with the seein g p r o f i l e used f o r NGC 1566. Thus i t appears t h a t t h e exact shape of the seein g p r o f i l e does not s t r o n g l y a f f e c t the r e s u l t s of the c o n v o l u t i o n , provided t h a t a reasonable approximation to the a c t u a l p r o f i l e i s used. The r e s u l t of the c o n v o l u t i o n i s shown i n Figure 24. The bulge model, before c o n v o l u t i o n , had a s u r f a c e b r i g h t n e s s d i s t r i b u t i o n (in magnitudes) of the form as can be seen, the convolved bulge p r o f i l e p r ovided a good f i t t o the ob s e r v a t i o n s i n the i n n e r 11". The convolved bulge p r o f i l e was s u b t r a c t e d from the i n i t i a l p r o f i l e , and the r e s i d u a l s a r e p l o t t e d i n F i g u r e 25. The i n n e r r e g i o n of t h i s p r o f i l e can be d e s c r i b e d by a Gaussian l u m i n o s i t y d i s t r i b u t i o n of the ferm JUCK. -/V.903 -f ,7?V^ (io) which i s very c l o s e to the slope of Eguation 3, which d e s c r i b e s the s u r f a c e b r i g h t n e s s d i s t r i b u t i o n of the nucleus of NGC 1566. However, the nucleus of NGC 1068 i s much b r i g h t e r , r e l a t i v e to the bulge, than i s t h a t of NGC 1566. Within an 8,5 diameter a p e r t u r e , the nucleus of NGC 1068 c o n t r i b u t e s about 15% of the t o t a l red l i g h t ( i n c l u d i n g H°<) , 90 as compared t o 5% f o r the nucleus of NGC 1566. The v i s u a l image of NGC 1068 was analyzed i n the same manner. The l u m i n o s i t y p r o f i l e i s l i s t e d i n Table 11 and p l o t t e d vs r'"* i n Fig u r e 29. T h i s p r o f i l e i s f i t t e d to a deVaucouleurs law f o r 4.'4<r<11". The r e s u l t s of the c o n v o l u t i o n of the bulge model with the seeing p r o f i l e o f F i g u r e 16 i s a l s o p l o t t e d i n F i g u r e 29. The bulge model, before c o n v o l u t i o n , was d e s c r i b e d by a l u m i n o s i t y d i s t r i b u t i o n of the form As b e f o r e , the convolved p r o f i l e was s u b t r a c t e d from the i n i t i a l p r o f i l e , and the r e s i d u a l s are p l o t t e d i n Fig u r e 30. I t i s not p o s s i b l e t o f i t t h i s r e s i d u a l p r o f i l e to a Gaussian l u m i n o s i t y d i s t r i b u t i o n . T h i s i s not s u r p r i s i n g i n c o n s i d e r a t i o n of the asymmetry of the inn e r contours of the v i s u a l image (Figure 26), apparently due to o b s c u r a t i o n by dust. T h i s r e s u l t a m p l i f i e s the suggestion of Lebofsky et a l (1978) t h a t the dust o b s c u r a t i o n renders the nucleus of NGC 1068 too f a i n t to be d i s t i n g u i s h e d from the surrounding s t a r s a t v i s u a l wavelengths. However, whereas Lebofsky et a l suggested t h a t the nucleus c o u l d not be observed at wavelengths l e s s than 1^, the p r o f i l e s d e r i ved here i n d i c a t e t h a t the p o i n t source component can be determined a t red wavelengths. 91 Figure 21: COMTAL v - r map f o r NGC 1068. The i n t e n s i t y s c a l e i s c o l o r -coded so that the reddest areas are those w i t h the l a r g e s t v - r , and the white areas are those w i t h the s m a l l e s t v - r . '93. 20-0 30-0 tH.D 5 0 . 0 6 0 . 0 70.0 8 0 . 0 90.0 ! M 0 n o t - J 1 1 1 1 I _ i I I I J_5 Figure 22: Isophotal contours for the red image of NGC 1068. Table JO Surface Brightness D i s t r i b u t i o n Of The B Imaqe Of NGC 1068 r (arcsec) (mag/o- ) 0.50 14. 19 0.77 14.35 1.00 14.51 1.2 2 14.67 1.44 14.83 1.67 14.99 1.93 15.16 2.28 15.32 2.55 15.48 2.92 15.64 3.39 15.80 3.97 16.97 4.57 16. 13 5.25 16. 29 6.01 16.45 6.73 16.64 7.57 16.77 8.49 17.94 9.56 17. 10 10.88 17.26 12.40 17.42 13.38 17.58 14.34 17.75 15.20 17.91 16.00 18.07 16.77 18. 23 17.46 18.39 9V r s ! " 4 4 4 4 4 4 i 4 4 * X H . u * " X H 4 • X c s i - l V * M » ft " , , 1 , I I 0 0 3 . 0 6 . 0 9 . 0 1 2 . 0 1 5 . 0 1 8 . 0 RflD (flRCSEC) Figure 23: Luminosity p r o f i l e s f or the red image of NGC 1068. The various p r o f i l e s are as follows: * = p r o f i l e derived from the contours of Figure 22. x =profile derived from the simulated aperture photometry * = p r o f i l e along P.A.135* (northwest along minor axis) * = p r o f i l e along P.A.315° (southeast along minor axis) <fS <y. Figure 24: Luminosity p r o f i l e f o r the red-H< image of NGC 1068, derived from the values of Table 10. The s t r a i g h t l i n e represents the observed deVaucouleurs law, described by the equation M*. - ft-Vf 3.237r''i The dots (») are the observed p r o f i l e , and the crosses (*) represent the convolved bulge model. O — n i i i i i 0.0 1.0 2.0 3.0 4.0 5.0 R A D ( A R C S E C ) Figure 25: Residual nucleus of the red image of NGC 1068 (H* emission subtracted). The s t r a i g h t l i n e i s described by the equation M903 t .7?^r^ Figure 26: Isophotal contours for the v i s u a l image of NGC 1068. The contour values and corresponding r a d i i are given i n Table 11. Table jn Surface Brightness Di s t r i b u t i o n Of The V Image Of NGC 1068 r (arcsec) (mag/a" ) 0.98 15.63 1.55 15.78 2. (15 15.93 2.66 16.08 3.05 16.22 3.41 16.36 3.77 16.50 4.16 16.63 4.57 16.77 5.06 16.90 5.62 17.04 6.26 17. 17 6.92 17.31 7.63 17.44 8.46 17.57 9.40 17.71 10.49 17.84 11.69 17.97 12.75 18. 10 13.66 18. 23 14.49 18.37 15.26 18.50 15.91 18.63 16.67 18.76 17.31 18.90 99 Figure 27: COMTAL p i c t u r e of the v i s u a l image of NGC 1068, magnified twice to show only the inner regions. The highest i n t e n s i t y areas are white, and the l e a s t i n t e n s i t y areas are red. If H 01 IOO ' J< ID O M • X H » ~ ~ r — 3 . 0 0 . 0 I— 6.0 9 . 0 1 2 . 0 R A D C f l R C S E C ) ) 5 . 0 16 .0 Figure 28: Luminosity p r o f i l e s f o r the v i s u a l image of NGC 1068. The v a r i o u s p r o f i l e s are marked as i n Figure 23. 101 at Figure 29: luminosity p r o f i l e f o r the v i s u a l image of NGC 1068, derived from the values of Table 11. The s t r a i g h t l i n e describes the observed deVaucouleurs law. The dots (•) are the observed p r o f i l e , and the crosses (*) are the convolved bulge model. lox r-'. .—o LU t o CJ QC az \ „ CD • C E 0 3 -I o o - l 0.0 1.0 2.0 3.0 RRD 4.0 (flRCSEC) 5.0 Figure 30: Residuals f o r the v i s u a l image of NGC 1068, a f t e r s u b t r a c t i n g the convolved bulge. 103 Figure 31: COMTAL p i c t u r e of the H<K image of NGC 1068; data converted to l o g ( i n t e n s i t y ) v alues. White areas are the h i g h e s t i n t e n s i t y , blue-red areas are the l e a s t i n t e n s i t y areas. 105 Um. D i s c u s s i o n The same caveat a t tached t o the a n a l y s i s of the NGC 1566 data a l s o a p p l i e s t o NGC 1068: the f a c t t h a t t h e p r o f i l e s o n l y extend t o about 18" adds a good d e a l of u n c e r t a i n t y to the c o n c l u s i o n s drawn. As ment ioned , i t i s not p o s s i b l e to d e r i v e any i n f o r m a t i o n about the d i s k component of NGC 1068 from the CCD d a t a . I t a l s o cannot be determined what i n f l u e n c e the very b r i g h t i n n e r s p i r a l arms have on the p r o f i l e , e x c e p t to say t h a t they o b v i o u s l y a f f e c t the p r o f i l e f o r r>11". However, the d i s c u s s i o n i n s e c t i o n 3 demonst ra tes t h a t the o u t e r d i s k would not a f f e c t the bulge p r o f i l e too g r e a t l y . W i t h i n these l i m i t a t i o n s , i t i s p o s s i b l e t o p r o v i d e some compar ison of the bulge component o f the red and v i s u a l images . E g u a t i o n s 9 and 11 show tha t the bulge i s r e d d e r i n the i n n e r r e g i o n than i n the o u t e r r e g i o n . The V magnitude o f the bu lge i n s i d e a 10" a p e r t u r e i s 13 .15 , and the V - E c o l o r i s 2 . 2 2 , much redder than the bu lge of NGC 1566. The E magnitude of the p o i n t source i s 13 .32 , but no V magnitude can be determined s i n c e the p o i n t source component i s not seen at v i s u a l wave lengths . The con tour p l o t s ( F i g u r e s 21 and 25) and the v - r image f o r NGC 1068 (F igure 21) show t h a t the red image e x h i b i t s a b a r - l i k e e l o n g a t i o n a long the major a x i s , which i s not p resen t i n the v i s u a l image. I f t h i s r e p r e s e n t s a d i s t i n c t s t r u c t u r a l component , then the f a c t t h a t i t i s p resent i n the red image 106 after the emission has been subtracted out indicates that i t consists of red stars rather than gas. Since the point source component of NGC 1068 i s much stronger than that of NGC 1566, the determination of t h i s feature i s not so dependent on the shape of the bulge p r o f i l e i n the inner region. Figure 3 3 shows the observed minus convolved residuals for the v i s u a l and red images of NGC 1068. For the red image, cr=. 004, and for the visu a l image, cr=.007, so the nuclear component of the red image i s very well-determined. A f i n a l point to arise from the analysis of t h i s data i s that the emission l i n e s contribute s i g n i f i c a n t l y to the t o t a l l i g h t from NGC 1068, and presumably from other Seyferts as well. This point w i l l be discussed further i n Chapter 4. 107 Chapter 4 Conclusions In section 4 of Chapters 2 and 3, the most s i g n i f i c a n t l i m i t a t i o n s of the analysis presented here have been emphasized. But a more fundamental guestion may also be raised. The luminosity d i s t r i b u t i o n "laws" which govern galaxies are purely empirical. There are very few observations of the c e n t r a l regions of galaxies of comparable guality to the CCD observations- For NGC 1566, for example, the isophotal contours of deVaucouleurs (1973), based on photographic plates, give very l i t t l e information about the inner 30". I t cannot be determined, therefore, i f these "laws" should be expected to adeguately describe the galaxy structure when very detailed observations are available. A related problem i s that the possible influence of s p i r a l arms or bars on the luminosity d i s t r i b u t i o n has not been s u f f i c i e n t l y considered. Clearly, dynamical models are needed to provide a better basis on which to derive a luminosity d i s t r i b u t i o n law. I t should be noted that the observations presented here and elsewhere (cf. Pritchet, 1979) indicate that the empirical laws do adeguately describe the observations, at l e a s t for very regular s p r i a l s and e l l i p t i c a l s . For a system such as NGC 1068 however, there are obvious and s i g n i f i c a n t deviations from these simple laws. For such cases, more information i s needed. 10? U *.IO I o '.05' y 5 4 + .10 .o5\ I - . © S L 5 «• " 7 Figure 33: Observed-Convolved resi d u a l s f o r the red and v i s u a l images of NGC 1068. The top fig u r e i s the red image, and the bottom fig u r e i s the v i s u a l image. 109 I t would be very h e l p f u l t o have more e x t e n s i v e p h o t o m e t r i c coverage of t h e s e and o t h e r S e y f e r t s . Two-dimensional o b s e r v a t i o n s i n 0, B, V, B, and I would p r o v i d e b e t t e r i n f o r m a t i o n about t h e c o l o r s of t h e v a r i o u s components. In p a r t i c u l a r , f o r NGC 1068 i t would be i n t e r e s t i n g t o see t o what e x t e n t t h e p o i n t s o u r c e i s o b s c u r e d a t 0 and B w a v e l e n g t h s , and how s t r o n g l y peaked i t i s a t I or l o n g e r w a v e l e n g t h s . The b a r - l i k e e l o n g a t i o n a l s o r e g u i r e s f u r t h e r i n v e s t i g a t i o n a t o t h e r wavelengths. More d e t a i l e d r a d i o mapping of NGC 1068 would determine i f t h i s s t r u c t u r e has any r a d i o c o u n t e r p a r t . I n a d d i t i o n , f o r any S e y f e r t g a l a x y , i t i s e s s e n t i a l t o have t w o - d i m e n s i o n a l narrow-band o b s e r v a t i o n s o f t h e e m i s s i o n l i n e s , t o d etermine how they a f f e c t the photometry. H<* and H/J o b s e r v a t i o n s c o u l d be used t o determine t h e d u s t d i s t r i b u t i o n . O b s e r v a t i o n s of t h e f o r b i d d e n l i n e s c o u l d p r o v i d e i n f o r m a t i o n about t h e d i f f e r e n t i o n i z a t i o n r e g i o n s . With the advent o f low n o i s e s o l i d s t a t e d e t e c t o r s , such as t h e CCD, such o b s e r v a t i o n s are much more f e a s i b l e . The g u e s t i o n posed i n C h a p t e r 1 of t h i s t h e s i s , "To what e x t e n t a r e S e y f e r t g a l a x i e s s t r u c t u r a l l y n o r mal?" must remain unanswered. The a n a l y s i s p r e s e n t e d f o r NGC 1566 and NGC 1068 does not r e v e a l any s t r u c t u r a l component unigue to t h e s e g a l a x i e s , a l t h o u g h the c o m p l i c a t e d s t r u c t u r e o f NGC 1068 and t h e l i m i t e d a r e a covered by the CCD o b s e r v a t i o n s d i d not p e r m i t a d i s k component t o be d e t e r m i n e d , and so a d e t a i l e d 110 comparison to be made. But more l i m i t i n g s t i l l i s the fact that not enough "normal" galaxies of these Hubble types have been studied with observations of t h i s guality with which to compare the Seyferts. Such observations should be made to make i t possible to answer t h i s guestion. I l l B i b l i o g r a p h y Adams, T. F. , 1977, Ap. J . Supplement, v.33 r p. 19. A l l e n , B. 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J . , v .18 , p.720. Z a s o v , A . V . , and V. M. l y u t y i , 1973, S o v i e t Ast ronomy-A. J . , v .17 , p .169 . 1 1 9 Appendix The l u m i n o s i t y p r o f i l e of a g a l a x y can be d e r i v e d from m u l t i - a p e r t u r e photometry f o l l o w i n g the procedure d e s c r i b e d by deV a u c o u l e u r s and deVaucouleurs (1974). B r i e f l y , t h e procedure c o n s i s t s of p l o t t i n g the p o i n t s d e t e r m i n e d from t h e photometry on a m a g n i t u d e - v s - a p e r t u r e graph, and f i t t i n g a smooth c u r v e t o t h e s e p o i n t s . V a l u e s of s u r f a c e b r i g h t n e s s as a f u n c t i o n o f d i s t a n c e can be d e r i v e d by n u m e r i c a l d i f f e r e n c i n g o f t h i s c u r v e , t h r o u g h t h e e g u a t i o n , n u l / The d e V a u c o u l e u r s do t h i s f o r the B photometry of NGC 1068.. However, an e x a m i n a t i o n of t h e photometry of NGC 1068 r e v e a l s s e v e r a l drawbacks t o t h i s p r o c e d u r e . To begin w i t h , t y p i c a l l y t he a c c u r a c y of p h o t o m e t r i c measurements i s no b e t t e r than .1 magnitude. An e r r o r of t h i s s i z e i s s u f f i c i e n t t o make a n o t i c e a b l e d i f f e r e n c e i n the d e r i v e d l u m i n o s i t y p r o f i l e . I n t h e case c f NGC 1068, t h e V photometry shows an even g r e a t e r s c a t t e r than t h i s ( F i g u r e 19), as much as 0.4 mag. As d i s c u s s e d i n s e c t i o n 2 of Chapter 3, t h i s i s p r o b a b l y due t o v a r i a b i l i t y o f the n u c l e u s . DeVaucouleurs and deV a u c o u l e u r s (1974) ac c o u n t f o r v a r i a b i l i t y i n NGC 4151 by s o r t i n g the p h o t o m e t r i c data a c c o r d i n g t o t h e time o f t h e o b s e r v a t i o n s , so t h a t o n l y o b s e r v a t i o n s t a k e n d u r i n g a p a r t i c u l a r l e v e l o f a c t i v i t y of the n u c l e u s a r e combined. For 120 NGC 1068, t h i s means t h a t each set of photometric data must be s e p a r a t e l y analyzed, s i n c e no two observers have c o i n c i d e n t measurements. In most cases, only 4 or 5 a p e r t u r e s i z e s were used. T h i s o b v i o u s l y i n t r o d u c e s s u b s t a n t i a l u n c e r t a i n t y i n the magnitude-aperture curve. F i g u r e 32 shows the l u m i n o s i t y p r o f i l e d e r i v e d from each s e t of published photometry f o r which 4 or more obs e r v a t i o n s were a v a i l a b l e . The data extends out to r=65" but only the i n n e r 30" are p l o t t e d . The d i s p e r s i o n i n the p r o f i l e s d e r i v e d from the v a r i o u s s e t s of photometry i s as much as 0.4 mag at l a r g e r a d i i . Within the r e g i o n covered by the CCD o b s e r v a t i o n s the d i s p e r s i o n i s as much as 0.2 mag. In attempting to match the CCD data t o these p r o f i l e s , the s i m u l a t e d a p e r t u r e photometry of the CCD v i s u a l image was used to d e r i v e a l u m i n o s i t y p r o f i l e . T h i s p r o f i l e f i t t e d the p r o f i l e s of F i g u r e 33 to w i t h i n the d i s p e r s i o n c i t e d . An attempt was made to decompose the mean p r o f i l e determined from F i g u r e 33, together with the CCD d a t a , i n t o a d i s k and bulge component using the procedure d e s c r i b e d i n Chapter 2. For t h i s data, no convergence was achieved a f t e r 20 i t e r a t i o n s . A f i n a l problem which i s encountered i n t h i s procedure i s t h a t the contours of NGC 1068 are h i g h l y asymmetric. The photometric models of course take no account of contour shape s i n c e they are based on o b s e r v a t i o n s through c i r c u l a r 121 a p e r t u r e s . Thus much of the i n f o r m a t i o n about the s t r u c t u r e o f th e g a l a x y i s l o s t i n t h i s p r o c e d u r e . There i s no co r r e s p o n d e n c e between t h i s method of d e r i v i n g a l u m i n o s i t y p r o f i l e and t h a t of u s i n g the c o n t o u r p l o t s t o d e r i v e an e g u i v a l e n t r a d i u s at each i n t e n s i t y l e v e l . F o r a g a l a x y w i t h so i r r e g u l a r a shape as NGC 1068, the p h o t o m e t r i c models w i l l n o t p r o v i d e a s u f f i c i e n t l y u n b i a s e d p r o f i l e t o make p o s s i b l e a u s e f u l comaprison w i t h t h e p r o f i l e d e r i v e d from the c o n t o u r s . /aa n it 11 H •X M k ~ " " 5 » ' «$"" JO a.s J» Figure 34: Luminosity p r o f i l e s d erived from the published photometry f o r the V observations of NGC 1068, together w i t h the CCB data Legend: H =Walker (1968) * =Penston et a l (1974) • =Westerlund and W a l l (1968) * =deVaucouleurs (1968) • =CCD data 

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