Multiwavelength Analysis of the Merging Galaxy Cluster

A115 is a merging galaxy cluster at z similar to 0.2 with a number of remarkable features, including a giant (similar to 2.5 Mpc) radio relic, two asymmetric X-ray peaks with trailing tails, and a peculiar line-of-sight velocity structure. We present a multiwavelength study of A115 using optical imaging data from Subaru, X-ray data from Chandra, and spectroscopic data from the Keck/DEIMOS and MMT/Hectospec instruments. Our weak-lensing (WL) analysis shows that the cluster is composed of two subclusters whose mass centroids are in excellent agreement with the two brightest cluster galaxy positions (less than or similar to 10 ''). By modeling A115 with a superposition of two Navarro-Frenk-White halos, we determine the masses of the northern and southern subclusters to be M-200 = 1.58(-0.49)(+0.56) x 10(14) M-circle dot and 3.15(-0.71)(+0.79) x 10(14) M-circle dot, respectively. Combining the two halos, we estimate the total cluster mass to be M-200 = 6.41(1.04)(+1.08) x 10(14) M-circle dot at = R-200 = 1.67(0.09)(+0.10) Mpc. These WL masses are significantly (a factor of 3-10) lower than what is implied by the X-ray and optical spectroscopic data. We attribute the difference to the gravitational and hydrodynamic disruption caused by the collision between the two subclusters.