A New Dissociative Galaxy Cluster Merger: RM J150822.0+575515.2

Abstract: Galaxy cluster mergers that exhibit clear dissociation between their dark matter, intracluster gas, and stellar components are great laboratories for probing dark matter properties. Mergers that are binary and in the plane of the sky have the additional advantage of being simpler to model, allowing for a better understanding of the merger dynamics. We report the discovery of a galaxy cluster merger with all these characteristics and present a multiwavelength analysis of the system, which was found via a search in the redMaPPer optical cluster catalog. We perform a galaxy redshift survey to confirm the two subclusters are at the same redshift (0.541, with $368\pm519$ km s$^{-1}$ line-of-sight velocity difference between them). The X-ray morphology shows two surface-brightness peaks between the BCGs. We construct weak lensing mass maps that reveal a mass peak associated with each subcluster. Fitting NFW profiles to the lensing data, we find masses of $M_{\rm 200c}=36\pm11\times10^{13}$ and $38\pm11\times10^{13}$ M$\odot/h$ for the southern and northern subclusters respectively. From the mass maps, we infer that the two mass peaks are separated by $520^{+162}{-125}$ kpc along the merger axis, whereas the two BCGs are separated by 697 kpc. We also present deep GMRT 650 MHz data to search for a radio relic or halo, and find none. Using the observed merger parameters, we find analog systems in cosmological n-body simulations and infer that this system is observed between 96-236 Myr after pericenter, with the merger axis within $28^{\circ}$ of the plane of the sky.