The Mass Distribution of the Unusual Merging Cluster Abell 2146 from Strong Lensing

TL;DR

This study uses strong gravitational lensing to map the mass distribution in the merging galaxy cluster Abell 2146, revealing that the dark matter halo is closely aligned with the brightest galaxy, despite the unusual X-ray core behavior.

Contribution

It provides the first strong lensing mass map of Abell 2146, showing the dark matter centroid's position relative to the BCG and X-ray cool core during a merger.

Findings

Dark matter centroid coincides with the BCG within 2 kpc.

The X-ray cool core leads the dark matter centroid by about 30 kpc.

Strong lensing constraints effectively map the mass distribution in merging clusters.

Abstract

Abell 2146 consists of two galaxy clusters that have recently collided close to the plane of the sky, and it is unique in showing two large shocks on $\textit{Chandra X-ray Observatory}$ images. With an early stage merger, shortly after first core passage, one would expect the cluster galaxies and the dark matter to be leading the X-ray emitting plasma. In this regard, the cluster Abell 2146-A is very unusual in that the X-ray cool core appears to lead, rather than lag, the Brightest Cluster Galaxy (BCG) in their trajectories. Here we present a strong lensing analysis of multiple image systems identified on $\textit{Hubble Space Telescope}$ images. In particular, we focus on the distribution of mass in Abell 2146-A in order to determine the centroid of the dark matter halo. We use object colours and morphologies to identify multiple image systems; very conservatively, four of these systems are used as constraints on a lens mass model. We find that the centroid of the dark matter halo, constrained using the strongly lensed features, is coincident with the BCG, with an offset of $\approx$ 2 kpc between the centres of the dark matter halo and the BCG. Thus from the strong lensing model, the X-ray cool core also leads the centroid of the dark matter in Abell 2146-A, with an offset of $\approx$ 30 kpc.