Probing of the Interactions Between the Hot Plasmas and Galaxies in Clusters from z=0.1 to 0.9

TL;DR

This study investigates how the spatial distributions of galaxies and hot plasma in galaxy clusters evolve from redshift 0.9 to 0.1, revealing that galaxies become more centrally concentrated over time.

Contribution

It provides the first detailed analysis of the evolution of galaxy and ICM spatial distributions in relaxed clusters across a wide redshift range using optical and X-ray data.

Findings

Galaxies become more concentrated towards cluster centers at lower redshifts.

The galaxy light to ICM mass ratio profile steepens with decreasing redshift.

The observed evolution is robust against systematic uncertainties.

Abstract

Based on optical and X-ray data for a sample of 34 relaxed rich clusters of galaxies with redshifts of 0.1-0.9, we studied relative spatial distributions of the two major baryon contents, the cluster galaxies and the hot plasmas. Using multi-band photometric data taken with the UH88 telescope, we determined the integrated (two dimensional) radial light profiles of member galaxies in each cluster using two independent approaches, i.e., the background subtraction and the color-magnitude filtering. The ICM mass profile of each cluster in our sample, also integrated in two dimensions, was derived from a spatially-resolved spectral analysis using XMM-Newton and Chandra data. Then, the radially-integrated light profile of each cluster was divided by its ICM mass profile, to obtain a profile of "galaxy light vs. ICM mass ratio". The ratio profiles over the central 0.65 R500 regions were found to steepen from the higher- to lower- redshift subsamples, meaning that the galaxies become more concentrated in the ICM sphere towards lower redshifts. The evolution is also seen in galaxy number vs. ICM mass ratio profiles. A range of systematic uncertainties in the galaxy light measurements, as well as many radius-/redshift- dependent biases to the galaxy vs. ICM profiles have been assessed, but none of them is significant against the observed evolution. Besides, the galaxy light vs. total mass ratio profiles also exhibit gradual concentration towards lower redshift. We interpret in the context that the galaxies, the ICM, and the dark matter components followed a similar spatial distribution in the early phase (z>0.5), while the galaxies have fallen towards the center relative to the others at a later phase.