Galaxy stellar populations and dynamics as probes of group evolution

The distribution of galaxy properties in groups and clusters holds important information on galaxy evolution and growth of structure in the Universe. While clusters have received appreciable attention in this regard, the role of groups as fundamental to formation of the present day galaxy population has remained relatively un-addressed. In this thesis we focus on the detailed analysis of properties in a single massive group, NGC5044, with the aim of reconstructing its formation history. New observations obtained using the Anglo-Australian Telescope and the multi-object fibre-fed AAOmega spectrograph are combined with available photometry and X-ray data, which are used to construct a significant catalogue of spectroscopically confirmed group-member galaxies down to MB ≈ −13.5. We define the NGC5044 group as hosting 111 spectroscopically confirmed member galaxies and a total dynamical mass of 9.2×1013M⊙. Of these 111 members, 67 have spectra from AAOmega and the 6dF Galaxy Survey of sufficient signal-to-noise to undertake a detailed investigation of their stellar populations. We find that galaxies in the NGC5044 group show evidence for a strong relationship between stellar mass and metallicity, consistent with their counterparts in both higher and lower mass groups and clusters. In the context of the group environment, our data support the tidal disruption of low-mass galaxies at small group-centric radii, as evident from an apparent lack of galaxies below ∼ 109M⊙ within ∼ 100 kpc of the brightest group galaxy. Using a joint analysis of absorptionand emission-line metallicities, we show that the star-forming galaxy population in the NGC5044 group appears to require gas removal to explain the ∼1.5 dex offset between absorption- and emission-line metallicities observed in some cases. A comparison with other stellar population properties suggests that this gas removal is dominated by galaxy interactions with the hot intragroup medium. The combination of galaxy dynamics, stellar populations and X-ray chemical abundances lead us to the conclusion that the bulk of the NGC5044 group assembled at early times through the coalescing of several smaller sub-groups, and has since evolved through relatively steady accretion of isolated galaxies or loose groups.