Late growth of early-type galaxies in low-z massive clusters

Abstract

We study a sample of 936 early-type galaxies (ETGs) located in 48 low-z regular galaxy clusters with $M_{200}\geq 10^{14}~ M_\odot$ at $z< 0.1$. We examine variations in the concentration index, radius, and color gradient of ETGs as a function of their stellar mass and loci in the projected phase space (PPS) of the clusters. We aim to understand the environmental influence on the growth of ETGs according to the time since infall into their host clusters. Our analysis indicates a significant change in the behavior of the concentration index $C$ and color gradient around $M_{\ast} \approx 2\times 10^{11} ~M_\odot \equiv \tilde{M}_{\ast}$. Objects less massive than $ \tilde{M}_{\ast}$ present a slight growth of $C$ with $M_{\ast}$ with negative and approximately constant color gradients in all regions of the PPS. Objects more massive than $ \tilde{M}_{\ast}$ present a slight decrease of $C$ with $M_{\ast}$ with color gradients becoming less negative and approaching zero. We also find that objects more massive than $ \tilde{M}_{\ast}$, in all PPS regions, have smaller $R_{90}$ for a given $R_{50}$, suggesting a smaller external growth in these objects or even a shrinkage possibly due to tidal stripping. Finally, we estimate different dark matter fractions for galaxies in different regions of the PPS, with the ancient satellites having the largest fractions, $f_{DM}\approx$ 65%. These results favor a scenario where cluster ETGs experience environmental influence the longer they remain and the deeper into the gravitational potential they lie, indicating a combination of tidal stripping + harassment, which predominate during infall, followed by mergers + feedback effects affecting the late growth of ancient satellites and BCGs.