Mass and Gas Profiles in A1689: Joint X-ray and Lensing Analysis

TL;DR

This study combines X-ray and lensing data to analyze the mass, temperature, and entropy profiles of galaxy cluster A1689, revealing a discrepancy between observed and predicted temperatures and insights into the cluster's entropy structure.

Contribution

It provides a joint analysis of X-ray and lensing data for A1689, highlighting temperature discrepancies and entropy profile characteristics in a relaxed galaxy cluster.

Findings

Lensing and X-ray mass profiles agree under hydrostatic equilibrium.

Observed temperature exceeds model predictions by ~30%.

Entropy profile follows a shallow power-law beyond the core.

Abstract

We carry out a comprehensive joint analysis of high quality HST/ACS and Chandra measurements of A1689, from which we derive mass, temperature, X-ray emission and abundance profiles. The X-ray emission is smooth and symmetric, and the lensing mass is centrally concentrated indicating a relaxed cluster. Assuming hydrostatic equilibrium we deduce a 3D mass profile that agrees simultaneously with both the lensing and X-ray measurements. However, the projected temperature profile predicted with this 3D mass profile exceeds the observed temperature by ~30% at all radii, a level of discrepancy comparable to the level found for other relaxed clusters. This result may support recent suggestions from hydrodynamical simulations that denser, more X-ray luminous small-scale structure can bias observed temperature measurements downward at about the same (~30%) level. We determine the gas entropy at 0.1r_{vir} (where r_{vir} is the virial radius) to be ~800 keV cm^2, as expected for a high temperature cluster, but its profile at >0.1r_{vir} has a power-law form with index ~0.8, considerably shallower than the ~1.1 index advocated by theoretical studies and simulations. Moreover, if a constant entropy ''floor'' exists at all, then it is within a small region in the inner core, r<0.02r_{vir}, in accord with previous theoretical studies of massive clusters.