The SAMI Galaxy Survey: stellar population gradients of central galaxies
  We examine the stellar population radial gradients (age, metallicity and
[$\alpha/$Fe]) of $\sim$ 100 passive central galaxies up to $\sim 2 R_e$. The
targeted groups have a halo mass range spanning from $11 <
\log(M_{200}/M_{\odot}) < 15$, in the SAMI Galaxy Survey. The main goal of this
work is to determine whether central galaxies have different stellar population
properties when compared to similarly massive satellite galaxies. We find
negative metallicity radial gradients, which become shallower with increasing
stellar mass. The age and [$\alpha$/Fe] gradients are consistent with zero or
slightly positive. [$\alpha$/Fe] gradients become more negative with increasing
mass, while age gradients do not show any significant trend with mass. We do
not observe a significant difference between the stellar population gradients
of central and satellite galaxies, at fixed stellar mass. The mean metallicity
gradients are $\overline{\Delta [Z/H]/\Delta \log(r/R_e)} = -0.25 \pm 0.03$ for
central galaxies and $\overline{\Delta [Z/H]/\Delta \log(r/R_e)} = -0.30 \pm
0.01$ for satellites. The mean age and [$\alpha$/Fe] gradients are consistent
between central and satellite galaxies, within the uncertainties, with a mean
value of $\overline{\Delta \textrm{log (Age/Gyr)}/\Delta \log(r/R_e)} = 0.13
\pm 0.03$ for centrals and $\overline{\Delta \textrm{log (Age/Gyr)}/\Delta
\log(r/R_e)} = 0.17 \pm 0.01$ for satellite and $\overline{\Delta
[\alpha/Fe]/\Delta \log(r/R_e)} = 0.01 \pm 0.03$ for centrals and
$\overline{\Delta [\alpha/Fe]/\Delta \log(r/R_e)} = 0.08 \pm 0.01$ for
satellites. This evidence suggests that the central region of central passive
galaxies form in a similar fashion to satellite passive galaxies, in agreement
with a two-phase formation scenario.
