Program: GN-2009B-Q-84

Fossil groups are thought to represent the end-state of galaxy evolution in isolated groups. In an evolutionary process lasting $\sim4$\,Gyr, dynamical friction causes all galaxies brighter than $M^*$ to merge. Since the dynamical friction timescale for galaxies fainter than $M^*$ and the cooling timescale of the IGM is longer than this, the end result is a massive galaxy surrounded by a small number of faint galaxies and situated in a halo of X-ray-emitting gas typical of a normal galaxy group. Models of fossil group formation predict that the fainter galaxies, after falling into the group, evolve passively, unlike the first-ranked galaxy that undergoes many mergers. This should result in markedly different stellar populations. We propose to use GMOS on Gemini North to test this model of fossil group formation. We will measure velocity dispersions and Lick index strengths (from H$\delta$ to Fe5335) to estimate the ages, metallicities and $\alpha$-element abundance ratios of the stellar populations of galaxies down to $m^*_\mathrm{R}+3$ in two low-$z$ fossil groups. Using this data we can compare the stellar populations in the first-ranked galaxy to those in the other galaxies.