Fitting of Photometry in S4G galaxies using DiskFit

Abstract

This thesis presents an in-depth structural analysis of infrared images of nearby galaxies and considers the difficulty of constraining the disk, bar, and bulge components in these galaxies. The Spitzer Survey of Stellar Structure in Galaxies (S4G) provides a view at a wavelength largely unaffected by extinction that probes the older stellar populations of 2352 galaxies, of which a subset of 316 galaxies are selected for analysis based on size and morphology. The non-parametric fitting algorithm DiskFit is first used to model the bar, bulge, and disk from S4G-like simulated galaxy images to validate DiskFit's effectiveness and assess its strengths and weaknesses on the subsample. DiskFit is easily able to recover input disk and bar properties, while struggling to recover the input bulge properties. After validating DiskFit on simulated galaxy images, DiskFit is then used to model the components of the S4G subsample, while comparing to existing models made using the parametric algorithm GALFIT from the literature. It is found that DiskFit and GALFIT constrain the bar and disk similarly for the majority of the subsample galaxies, but the bulges are recovered differently. Most of the models with the two algorithms agree well, but many of them fail in either DiskFit or GALFIT. It is suggested that the verification of an algorithm on a relevant set of models is necessary, that parameterizing all of the bars with the same functional form is not optimal for all galaxies, and that the large scatter between values recovered in DiskFit and GALFIT relative to the mean uncertainty values returned by DiskFit's bootstrap resampling technique implies a reconsideration of how uncertainties are handled when constraining these components, in order to test current models of galaxy formation and evolution.