2MASX J19381810+5409402 , the SIMBAD biblio

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 intracluster medium (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 versus ICM mass ratio." When the sample is divided into three subsamples with redshift intervals of z = 0.11-0.22, 0.22-0.45, and 0.45-0.89, 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 toward lower redshifts. A Kolmogorov-Smirnov test indicates that this evolution in the cluster structure is significant on ≥ 94% confidence level. A range of systematic uncertainties in the galaxy light measurements, as well as many radius-/redshift-dependent biases to the galaxy versus ICM profiles, have been assessed, but none of them are significant against the observed evolution. Besides, the galaxy light versus total mass ratio profiles also exhibit gradual concentration toward lower redshift. We interpret 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 toward the center relative to the others. Such galaxy infall is likely to be caused by the drag exerted from the ICM to the galaxies as they move through the ICM and interact with it, while gravitational drag can enhance the infall of the most massive galaxies.