Stellar population gradients in early-type cluster galaxies
  We present a study of internal stellar population gradients in early-type
cluster galaxies. Using the VLT VIMOS integral field unit, we observed 19
galaxies in the core of the Shapley Supercluster (z = 0.048). The radial trends
in nine absorption lines (HdF to Fe5406) were measured to the effective radius
for 14 galaxies, from which we derived the gradients in age, total metallicity
and alpha-element over-abundance. We combine these with results from 11
galaxies studied in our previous VIMOS work (Rawle et al 2008). We observe a
mean metallicity gradient of -0.13 +/- 0.04 per dex and, in common with the
findings of previous studies, galaxies with log(sigma) > 2.1 have a sizeable
intrinsic scatter in metallicity gradient. The mean log(age/Gyr) gradient is
-0.02 +/- 0.06 per dex, although several galaxies have significant positive or
negative age gradients. The mean gradient in alpha-element enhancement is -0.10
+/- 0.04 per dex. We find that stellar population gradients are primarily
related to the central metallicity: early-type galaxies with super-solar
centres have steep negative metallicity gradients and positive age gradients;
those with solar metallicity centres have negligible [Z/H] gradients and
negative age gradients. There is a strong observed anti-correlation between the
gradients in age and metallicity. While a part of this trend can be attributed
to the correlation of measurement errors, we demonstrate that there is an
underlying intrinsic relation. For the Shapley galaxies, B-R colour gradients
predicted from spectroscopic age and metallicity generally agree well with
those measured directly from photometry.
