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

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 $T_X=8.5_{-0.9}^{+1.1}$ 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 $76\pm 364$ 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 $\approx 2$.