Separating Galaxies from the Cluster Dark Matter Halo in Abell 611

TL;DR

This study refines the mass estimates of galaxies and dark matter in Abell 611's core by combining strong lensing, velocity dispersions, and surface brightness analysis, revealing the importance of spectroscopic data.

Contribution

It introduces a combined lensing and velocity dispersion approach to accurately separate galaxy and dark matter halo masses in a galaxy cluster.

Findings

Velocity dispersions tighten mass constraints.

Neglecting velocity dispersions overestimates galaxy mass by 50%.

Surface brightness analysis improves galaxy mass parameter constraints.

Abstract

We investigate the mass content of galaxies in the core of the galaxy cluster Abell 611. We perform a strong lensing analysis of the cluster core and use velocity dispersion measurements for individual cluster members as additional constraints. Despite the small number of multiply-imaged systems and cluster members with central velocity dispersions available in the core of A611, the addition of velocity dispersion measurements leads to tighter constraints on the mass associated with the galaxy component, and as a result, on the mass associated with the dark matter halo. Without the spectroscopic velocity dispersions, we would overestimate the mass of the galaxy component by a factor of $\sim1.5$, or, equivalently, we would underestimate the mass of the cluster dark halo by $\sim5\%$. We perform an additional lensing analysis using surface brightness (SB) reconstruction of the tangential giant arc. This approach improves the constraints on the mass parameters of the 5 galaxies close to the arc by up to a factor $\sim10$. The galaxy velocity dispersions resulting from the SB analysis are consistent at the 1$\sigma$ confidence level with the spectroscopic measurements and with the prediction from the simple pointlike analysis. In contrast the truncation radii for 2-3 galaxies depart significantly from the galaxy scaling relation and suggest differences in the stripping history from galaxy to galaxy.