A Very Rich Bimodal Galaxy Cluster Merger: RXC J0032.1+1808

Abstract

The galaxy cluster RXC J0032.1+1808 has been well-studied with optical imaging and gravitational lensing mass maps, both of which reveal an elongated morphology in the north-south direction. We find that its X-ray morphology is bimodal, suggesting that it is in the process of merging; combined with a previously reported detection of a radio relic, we suggest that the system is seen after first pericenter. We extract the global X-ray temperature and unabsorbed luminosity from archival XMM-Newton data, finding $T_X=8.5^{+1.1}_{-0.9}$ keV and $L_X=1.04 \pm 0.03 \times 10^{45}$ erg s$^{-1}$ at 90\% confidence in the $0.5$--$10.0$ keV energy range. We conduct a redshift survey of member galaxies and find that the line-of-sight relative velocity between the two subclusters is $76\pm364$ km/s. We use publicly available hydrodynamic simulations to show that it cannot be a head-on merger, that it is observed ${\approx}395$--560 Myr after pericenter, and that the viewing angle must be one that foreshortens the apparent subcluster separation by a factor ${\approx}2$.