RESOLVING THE DISCREPANCY BETWEEN LENSING AND X-RAY MASS ESTIMATES OF THE COMPLEX GALAXY CLUSTER ABELL 1689

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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 × 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 northeastern 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 misinterpretations 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 ≈1Mpc). The obtained cluster mass within ≈875 kpc derived from X-rays alone is (6.4 ± 2.1) × 1014 M ☉ compared to a weak lensing mass of (8.6 ± 3.0) × 1014 M ☉ within the same radius.
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