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UBC Theses and Dissertations

Evolution of galaxies in compact groups de Oliveira, Claudia M.

Abstract

This thesis presents new observations of the complete sample of galaxies in Hickson Compact Groups and combines these observations with various previous works to attempt to answer some fundamental questions about the nature, history, and dynamical state of these groups. The new data consist of radial velocities and surface photometry of individual galaxies and velocity dispersions and complete membership information for the groups. The results of this thesis strongly suggest that most Hickson Compact Groups are physically associated systems and that the galaxy morphologies in these groups have been considerably altered by dynamical effects within the groups. The red shift survey of 99% of the galaxies in the Hickson Compact Group catalogue was completed. More than 84% of the galaxies have velocities within 1000 km s-1of the median velocity of the group. Ninety-two groups have at least three accordant members, and 69 groups have at least four. The radial velocities of the groups range from 1380 km s1 to 41731 km s-1 with a median of 8889 km s-1, corresponding to a median distance of 89 el Mpc (h = H0/100 km s-1 Mpc-1, where H0 is the Hubble constant). The median projected radial velocity dispersion of the groups is 207 km s-1, comparable to values reported for loose groups. The numbers, sizes, magnitudes and morphological types of the discordant galaxies in the Hickson Compact Groups are what is expected if these are due to chance alignments of unrelated galaxies projected on the group. An isophotal analysis of 140 early-type galaxies and visual inspection of another 242 galaxies in Hickson Compact Groups revealed many peculiarities in their morphologies. About 43% of the galaxies show morphological and/or kinematical distortions indicative of interactions and/or mergers. About 32% of the groups have three or more galaxies which show some sign of interaction. This is a lower limit, since for the great majority of the galaxies in the groups only imaging and low-resolution spectra are available. For the sub sample of 16 groups for which kinematical data are also available the fraction of interacting groups with three or more galaxies is 75%. About 11% of the elliptical galaxies in the Hickson Compact Groups have significant structural differences compared with typical cluster and field galaxies. They have enlarged characteristic radii and shallower surface brightness profiles. The luminosity function of galaxies in compact groups and of groups as a whole were derived, using Monte Carlo simulations to model the selection effects of the sample. The luminosities of compact group galaxies are consistent with their being drawn from a Schechter luminosity function with a = --0.21.1 L* = 1.1 ± 0.2 x 1010 h-2 Lo(M*=-19.6 + 5 log h) and (1)* = 1.31.1 x 10-4 h3 Mpc-3 (99% confidence level).Individual morphological—type luminosity functions were also determined. Both the total and the morphological type—specific luminosity function of compact group galaxies are significantly different from those of field, loose group and cluster galaxies. In particular, the luminosity function of elliptical galaxies in compact groups has a mean magnitude which is significantly brighter than the mean magnitude of Virgo cluster elliptical galaxies.

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