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 slowrotating 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 (medianand 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 ∼ 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 ) from the ATLAS 3D survey (median [Z/H] = 0.04 ± 0.07, ∆[Z/H] = −0.19 ± 0.1). However, massive early-type galaxies from ATLAS 3D have consistently old ages (median Age = 12.0 ± 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.

Sizes, colour gradients and resolved stellar mass distributions for the massive cluster galaxies in XMMUJ2235-2557 atz= 1.39

“…The age gradients in local passive galaxies are consistent with 0 (or slightly positive), while the average metallicity gradient is found to be of ∇ Z ≈ −0.1 to −0.3 (see also Mehlert et al 2003;Wu et al 2005;La Barbera & de Carvalho 2009). This result is also supported by recent studies with integral field spectroscopy (e.g Kuntschner et al 2010;González Delgado et al 2014;Oliva-Altamirano et al 2015;Wilkinson et al 2015). Our (U − R) and (g − r) colour gradient measurements alone unfortunately do not allow us to break the age-metallicity degeneracy.…”

Rhapsody-G simulations – II. Baryonic growth and metal enrichment in massive galaxy clusters

“…‚ The stellar mass in the central regions compares well to that measured for brightest cluster galaxies (Oliva-Altamirano et al 2015), but the modest (" 5 kpc) spatial resolution of the simulations artificially enhances tidal stripping, leading to a massive extended stellar halo.…”

A counter-image to the gravitational arc in Abell 1201:Evidence for IMF variations, or a 10 10 M ⊙ black hole?

“…The > ∼ 60 per cent variation required in Υ is larger than the ∼10 per cent attributable to typical age and metallicity gradients in massive ellipticals and BCGs (Kuntschner et al 2010;Oliva-Altamirano et al 2015). Hence this model appears to require radial gradients in the IMF; for example a factor of 1.55 in Υ corresponds to the difference between a Kroupa (2001) and an extrapolated Salpeter (1955) IMF.…”