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 $T_X=8.5_{-0.9}^{+1.1}$ keV and $L_X=1.04\pm 0.03\times 10^{45}$ erg s${}^{-1}$ at 90% confidence in the 0.5-10 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 1002-1785 km/s at 68% confidence, although the BCGs have an even larger difference of 2466 km/s. We use publicly available hydrodynamic simulations to show that it cannot be a head-on merger; it is consistent with an impact parameter of 0.5 or 1 Mpc. We also use the simulation set to find initial constraints on the time since pericenter ($\approx$315-550 Myr) and the locus of possible lines of sight.

arXiv commentThis version, accepted to ApJ, substantially revises the LOS relative velocity inference and includes a new figure, but with little change to other conclusions. From arXiv v2 to v3 the only change is a metadata correction