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Paola Oliva-Altamirano added section_Results_We_present_here__.tex
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\section{Results}
We present here the main results from our BCG stellar population analysis.
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\subsection{Central Stellar Populations}\label{sec:age_met}
Our stellar population measurements come from a luminosity-weighed distribution, therefore our results are sensitive to the brightest and youngest population of stars in the galaxy \citep[e.g.][]{TRAGER09}. The central values are measured in an aperture of $0.2\pm0.03~$R$_e$ and are given in Table \ref{tab:central}. We find that 6 out of 9 BCGs (67 per cent of the sample) have central intermediate ages (5 Gyr < Age < 10 Gyr), and 3 out of 9 (33 per cent of the sample) are centrally old (Age > 11 Gyr). The median central age is $8.9\pm3.3$~Gyr. The BCGs have homogeneous super-solar metallicities (median $[$Fe/H$]_{[\alpha/Fe]=0}= 0.13\pm0.07$) in their central regions.
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Fig \ref{fig:central} shows the central metallicities (upper panel) and ages (lower panel) as a function of galaxy mass. The SR and FR BCGs are presented as green-filled squares and red-open squares respectively. The companion galaxies (all FRs) are shown as open stars. We do not find any significant difference between the SRs and FRs, consistent with \citet{ATLAS3D}. The crosses represent the central stellar populations of the early-type galaxies in the ATLAS$^{3D}$ sample \citep[][]{ATLAS3D}. From a Kolmogorov~-~Smirnov (K-S) test we find that the hypothesis that the massive early-type galaxy metallicities and BCG metallicities come from the same distribution, can not be rejected at a 10 per cent confidence level (P-value 0.11). The BCGs have similar central metallicities (median $[$Fe/H$]_{[\alpha/Fe]=0}= 0.13\pm0.07$) to early-type galaxies in ATLAS$^{3D}$ (median [Z/H]~$= 0.04\pm0.07$) at fixed mass.
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The BCGs have slightly younger central ages (median Age~$=8.9\pm3.3$~Gyr) compared to the ATLAS$^{3D}$ galaxies at the same mass (median Age~$=12.0\pm3.8$~Gyr). From a K-S test we find that the age distribution of early-type galaxies and BCGs are different (P-value $1.2\times10^{-6}$). We also find that the BCGs have similar central stellar populations to the companion galaxies.
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In summary, our sample BCGs show homogeneous central metallicities and a wide range of ages. They show similar metallicities to other early-type galaxies of similar mass.
