Stellar Populations of BCGs, Close Companions and Intracluster Light in Abell 85, Abell 2457 and IIZw108

TL;DR

This study uses integral field spectroscopy to analyze the stellar populations of Brightest Cluster Galaxies and intracluster light in three galaxy clusters, revealing diverse formation histories and the presence of young, metal-poor stars in the ICL.

Contribution

First integral field spectroscopic survey of BCGs and ICL in three clusters, providing new insights into their stellar populations and formation mechanisms.

Findings

ICL contains old, metal-rich and significant young, metal-poor stars.

Different clusters show varied evolutionary stages and merger histories.

Young, metal-poor stars are absent in merging galaxies but present in ICL.

Abstract

We present the first results from an integral field (IFU) spectroscopic survey of a 75kpc region around three Brightest Cluster Galaxies (BCGs), combining over 100 IFU fibres to study the intracluster light (ICL). We fit population synthesis models to estimate age and metallicity. For Abell 85 and Abell 2457, the ICL is best-fit with a fraction of old, metal-rich stars like in the BCG, but requires 30-50% young and metal-poor stars, a component not found in the BCGs. This is consistent with the ICL having been formed by a combination of interactions with less massive, younger, more metal-poor cluster members in addition to stars that form the BCG. We find that the three galaxies are in different stages of evolution and may be the result of different formation mechanisms. The BCG in Abell 85 is near a relatively young, metal-poor galaxy, but the dynamical friction timescale is long and the two are unlikely to be undergoing a merger. The outer regions of Abell 2457 show a higher relative fraction of metal-poor stars, and we find one companion, with a higher fraction of young, metal-poor stars than the BCG, which is likely to merge within a gigayear. Several luminous red galaxies are found at the centre of the cluster IIZw108, with short merger timescales, suggesting the system is about to embark on a series of major mergers to build up a dominant BCG. The young, metal-poor component found in the ICL is not found in the merging galaxies.