Age and metallicity gradients in fossil ellipticals
  Fossil galaxy groups are speculated to be old and highly evolved systems of
galaxies that formed early in the universe and had enough time to deplete their
$L^{*}$ galaxies through successive mergers of member galaxies, building up one
massive central elliptical, but retaining the group X-ray halo. Considering
that fossils are the remnants of mergers in ordinary groups, the merger history
of the progenitor group is expected to be imprinted in the fossil central
galaxy (FCG). We present for the first time radial gradients of single-stellar
population (SSP) ages and metallicites in a sample of FCGs to constrain their
formation scenario. Our sample comprises some of the most massive galaxies in
the universe exhibiting an average central velocity dispersion of
$\sigma_0=271\pm28$ km s$^{-1}$. Metallicity gradients are throughout negative
with comparatively flat slopes of $\nabla_{[\rm{Fe/H}]}=- 0.19\pm0.08$ while
age gradients are found to be insignificant ($\nabla_{\rm{age}}=0.00\pm0.05$).
All FCGs lie on the fundamental plane, suggesting that they are virialised
systems. We find that gradient strengths and central metallicities are similar
to those found in cluster ellipticals of similar mass. The comparatively flat
metallicity gradients with respect to those predicted by monolithic collapse
($\nabla_{Z}=-0.5$) suggest that fossils are indeed the result of multiple
major mergers. Hence we conclude that fossils are not 'failed groups' that
formed with a top heavy luminosity function. The low scatter of gradient slopes
suggests a similar merging history for all galaxies in our sample.
