The Stellar Populations of Bright Coma Cluster Galaxies
  In this paper we study the stellar populations of 356 bright, $M_{r}$ $\leq$
-19, Coma cluster members located in a 2 degree field centred on the cluster
core using SDSS DR7 spectroscopy. For the quiescent galaxies we find strong
correlations between absorption line index strength and velocity dispersion
($\sigma$) for CN2, C4668, Mgb and H$\beta$. We find significant
cluster-centric radial gradients in H$\beta$, Mgb and C4668 for the passive
galaxies. We use state-of-the-art stellar population models \citep{schiavon07}
and the measured absorption line indices to infer the
single-stellar-population-equivalent (SSP-equivalent) age and [Fe/H] for each
galaxy, as well as their abundance patterns in terms of [Mg/Fe], [C/Fe], [N/Fe]
and [Ca/Fe]. For the passive galaxy subsample we find strong evidence for
"archaeological downsizing", with age $\propto \sigma^{0.90 \pm 0.06}$. We
recover significant cluster-centric radial stellar population gradients for the
passive sample in SSP-equivalent age, [Mg/Fe], [C/Fe] and [N/Fe]. These trends
are in the sense that, at fixed velocity dispersion, passive galaxies on the
outskirts of the cluster are 24% $\pm$ 9% younger with lower [Mg/Fe] and [N/Fe]
but higher [C/Fe] than those in the cluster core. We find no significant
increase in cluster-centric radial stellar population gradients when fitting to
a passive galaxy subset selected to cover the cluster core and South-West
region, which contains the NGC 4839 subgroup. Thus we conclude that the NGC
4839 in-fall region is not unique, at least in terms of the stellar populations
of bright galaxies. We speculate that the more pronounced cluster-centric
radial gradients seen by other recent studies may be attributed to the
luminosity range spanned by their samples, rather than to limited azimuthal
coverage of the cluster.(abridged)
