Resolving the discrepancy between lensing and X-ray mass estimates of the complex galaxy cluster Abell 1689

TL;DR

This study uses combined X-ray and gravitational lensing data to resolve the long-standing mass discrepancy in galaxy cluster Abell 1689, demonstrating consistency when analyzing the main, symmetric cluster component.

Contribution

The paper provides a detailed analysis showing that excluding substructure from the X-ray mass estimate aligns it with lensing measurements, resolving previous discrepancies.

Findings

X-ray and lensing mass profiles agree for the main cluster component

Excluding substructure from analysis reduces mass estimate discrepancies

Mass within 875 kpc is approximately 6.4 x 10^14 solar masses from X-rays and 8.6 x 10^14 from lensing

Abstract

There is a long-standing discrepancy between galaxy cluster masses determined from X-ray and gravitational lensing observations of which Abell 1689 is a well-studied example. In this work we take advantage of 180 ks of Chandra X-ray observations and a new weak gravitational study based on a Hubble Space Telescope mosaic covering the central 1.8 Mpc x 1.4 Mpc to eliminate the mass discrepancy. In contrast to earlier X-ray analyses where the very circular surface brightness has been inferred as Abell 1689 being spherically symmetric and in hydrostatic equilibrium, a hardness ratio map analysis reveals a regular and symmetric appearing main clump with a cool core plus some substructure in the North Eastern part of the cluster. The gravitational lensing mass model supports the interpretation of Abell 1689 being composed of a main clump, which is possibly a virialized cluster, plus some substructure. In order to avoid complications and mis-interpretations due to X-ray emission from the substructure, we exclude it from the mass reconstruction. Comparing X-ray and lensing mass profiles of the regular main part only, shows no significant discrepancy between the two methods and the obtained mass profiles are consistent over the full range where the mass can be reconstructed from X-rays (out to approx. 1 Mpc). The obtained cluster mass within approx. 875 kpc derived from X-rays alone is 6.4 plus/minus 2.1 x 10^14 solar masses compared to a weak lensing mass of 8.6 plus/minus 3.0 x 10^14 solar masses within the same radius.