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Parada Torres, Javiera Fernanda

University of British Columbia

This thesis introduces two new extragalactic distance determination methods; the first uses the median magnitude of carbon-rich asymptotic giant branch stars (CS), while the second uses the combined luminosity function of the red-giant branch (RGB) and oxygen-rich asymptotic giant branch stars (AGB). The sample of CS and RGB+AGB stars are selected from near-infrared JHKs-bands colour-magnitude diagrams (CMD), as in these filters RGs are bright and easy to identify. Both methods use the Magellanic Clouds (MC) as the fundamental calibrators and are tested in four Magellanic type galaxies: NGC 6822, IC 1613, WLM and NGC 3109, these target galaxies are all members of the Local Group. For the CS method, the CS J-band luminosity function is fitted using a Lorentzian distribution modified to allow the distribution to be asymmetric. The parameters of the best-fit distribution are then used to determine if the CS luminosity function of a given galaxy resembles that of the Large or Small MC (LMC or SMC). Based on this resemblance, either the LMC or SMC is used as the calibrator and the distance to the given galaxy is estimated using the median J-magnitude of the CS samples. The second method uses an un-binned maximum likelihood estimator to find the distance modulus that minimizes the difference between the luminosity function of the RGB+AGB stars in a target galaxy and the model distribution given by the luminosity function of the RGB+AGB stars in the MC. The model luminosity function can be given by the LMC and SMC individually or as a linear combination (LC) of both. The LC includes a "shape'' parameter that quantifies how "LMC-'' or "SMC-like'' a target galaxy is. Except for the NGC 3109 Ks luminosity function, the LC "shape'' results agree with the CS "LMC/SMC-like'' classification. Estimations of the distances through the tip of the RGB method are also included to test the performance and compare the results when the three different methods are applied to the same data set. The distance estimates for the target galaxies from the three different methods presented in this thesis are in good agreement within the error bars.

Text

2022-07-29

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/82226

Astronomy

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/