# Abell 315: reconciling cluster mass estimates from kinematics, X-ray, and lensing

## TL;DR

This study refines the mass estimate of galaxy cluster Abell 315 by accounting for substructures, reconciling discrepancies between kinematic, X-ray, and lensing measurements, and showing it is not underluminous in X-ray.

## Contribution

The paper introduces a detailed analysis of substructures in Abell 315, leading to revised mass estimates that align different measurement methods and challenge previous classifications.

## Key findings

- Cluster mass from kinematics reduced by a factor of 4 after accounting for substructures.
- Cluster mass concentration is unusually low, c200 <~ 1.
- Revised mass estimates agree with X-ray scaling relations, indicating no X-ray underluminosity.

## Abstract

Determination of cluster masses is a fundamental tool for cosmology. Comparing mass estimates obtained by different probes allows to understand possible systematic uncertainties. The cluster Abell 315 is an interesting test case, since it has been claimed to be underluminous in X-ray for its mass (determined via kinematics and weak lensing). We have undertaken new spectroscopic observations with the aim of improving the cluster mass estimate, using the distribution of galaxies in projected phase space. We identified cluster members in our new spectroscopic sample. We estimated the cluster mass from the projected phase-space distribution of cluster members using the MAMPOSSt method. In doing this estimate we took into account the presence of substructures that we were able to identify. We identify several cluster substructures. The main two have an overlapping spatial distribution, suggesting a (past or ongoing) collision along the line-of-sight. After accounting for the presence of substructures, the mass estimate of Abell 315 from kinematics is reduced by a factor 4, down to M200=0.8 (-0.4,+0.6) x 10^14 Msun. We also find evidence that the cluster mass concentration is unusually low, c200=r200/r-2 <~ 1. Using our new estimate of c200 we revise the weak lensing mass estimate down to M200=1.8 (-0.9,+1.7) x 10^14 Msun. Our new mass estimates are in agreement with that derived from the cluster X-ray luminosity via a scaling relation, M200=0.9+-0.2 x 10^14 Msun. Abell 315 no longer belongs to the class of X-ray underluminous clusters. Its mass estimate was inflated by the presence of an undetected subcluster in collision with the main cluster. Whether the presence of undetected line-of-sight structures can be a general explanation for all X-ray underluminous clusters remains to be explored using a statistically significant sample.