Multiwavelength 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 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 (≲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 ^+0.56 _-0.49 × 10 ¹⁴ M _⊙ and 3.15 ^+0.79 _-0.71 × 10 ¹⁴ M _⊙ , respectively. Combining the two halos, we estimate the total cluster mass to be M ₂₀₀ = 6.41 ^+1.08 _-1.04 × 10 ¹⁴ M _⊙ at R ₂₀₀ = 1.67 ^+0.10 _-0.09 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.