The accretion histories of brightest cluster galaxies from their stellar population gradients

Abstract

We analyse the spatially-resolved stellar populations of 9 local ($z<0.1$) Brightest Cluster Galaxies (BCGs) observed with VIMOS in IFU mode. Our sample is composed of 7 slow-rotating and 2 fast-rotating BCGs. We do not find a connection between stellar kinematics and stellar populations in this small sample. The BCGs have shallow metallicity gradients (median $\Delta$[Fe/H] $=-0.11\pm 0.1$), high central metallicities (median $[$Fe/H]${}_{[\alpha /Fe]=0}=0.13\pm 0.07$), and a wide range of central ages (from 5 to 15 Gyr). We propose that the reason for this is diverse evolutionary paths in BCGs. 67 per cent of the sample (6/9) show $\sim 7$ Gyr old central ages, which reflects an active accretion history, and 33 per cent of the sample (3/9) have central ages older than 11 Gyr, which suggest no star formation since $z=2$. The BCGs show similar central stellar populations and stellar population gradients to early-type galaxies of similar mass (M${}_{dyn}>10^{11.3}$M${}_{\odot }$) from the ATLAS${}^{3D}$ survey (median [Z/H] $=0.04\pm 0.07$, $\Delta$[Z/H] $=-0.19\pm 0.1$). However, massive early-type galaxies from ATLAS${}^{3D}$ have consistently old ages (median Age $=12.0\pm 3.8$Gyr). We also analyse the close massive companion galaxies of two of the BCGs. These galaxies have similar stellar populations to their respective BCGs.

Accepted for publication, MNRAS, March 3, 2015

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