Weak-Lensing Analysis of the Galaxy Cluster Abell 85: Constraints on the Merger Scenarios of Its Southern Subcluster

Abell 85 is a nearby (z=0.055) galaxy cluster that hosts a sloshing cool core, a feature commonly reported in relaxed clusters. However, the presence of multiple past and ongoing mergers indicates that it is an active node within the Abell 85/87/89 complex. We present a weak gravitational lensing (WL) analysis using Subaru Hyper Suprime-Cam imaging data to understand its assembly history by investigating the dark matter components of the substructures. Our mass reconstruction resolves three substructures associated with the brightest cluster galaxy (main), the southern (S) subcluster, and the southwestern (SW) subcluster, with WL peak significances of $> 6\sigma$, $> 5\sigma$, and $> 4\sigma$, respectively. The location of these mass peaks are consistent with those of the member galaxies. We estimate the masses of the main cluster ($M_{200c,main} = 2.91 \pm 0.72 \times 10^{14}\ M_\odot$) and the S subcluster ($M_{200c,S} = 1.23 \pm 0.52 \times 10^{14}\ M_\odot$) by fitting a multi-halo Navarro-Frenk-White profile. This $\sim$2:1 mass ratio indicates that the system is undergoing a major merger that is actively shaping the current dynamical state of Abell 85. Incorporating X-ray observations, we discuss the merger phase of the S subcluster and further examine the star-forming activity along the putative filament extending southeast of Abell 85.