Multi-wavelength analysis of the merging galaxy cluster A115

A115 is a merging galaxy cluster at z ∼ 0.2 with a number of remarkable features including a giant (∼2.5 Mpc) radio relic, two asymmetric X-ray peaks with trailing tails, and a peculiar line-of-sight velocity structure. We present a multi-wavelength 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 analysis shows that the cluster is comprised of two subclusters whose mass centroids are in excellent agreement with the two BCG positions (≾ 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 M₂₀₀ = 1.58^+0.56_−0.49 × 10¹⁴M_☉ and 3.15^+0.79_−0.71 × 10¹⁴M_☉, respectively. Combining the two halos, we estimate the total cluster mass to be M₂₀₀ = 6.41^+1.08_−1.04 × 10¹⁴M_☉ at R₂₀₀ = 1.67^+0.10_−0.09 Mpc. These weak-lensing 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.