The cluster lens ACO 1703: redshift contrast and the inner profile

TL;DR

This study explores the mass profile of galaxy cluster ACO 1703 using multiple lens models and source redshifts, revealing the importance of redshift contrast in constraining the inner mass distribution and supporting universal profiles.

Contribution

It demonstrates how including multiple source redshifts constrains the cluster's mass profile, addressing model non-uniqueness and supporting universal density profiles.

Findings

Models with full redshift range show  ho  r^{-1} profile

Omitting key sources allows steeper or shallower profiles

Redshift contrast provides robust mass measurements

Abstract

ACO 1703 is a cluster recently found to have a variety of strongly lensed objects: there is a quintuply-imaged system at z=0.888 and several other lensed objects from z=2.2 to 3.0 (the cluster itself is at z=0.28). It is not difficult to model the lens, as previous work has already done. However, lens models are generically non-unique. We generate ensembles of models to explore the non-uniqueness. When the full range of source redshifts is included, all models are close to \rho \propto r^{-1} out to 200 kpc. But if the quint is omitted, both shallower and steeper models (e.g., \rho \propto r^{-2}) are possible. The reason is that the redshift contrast between the quint and the other sources gives a good measurement of the enclosed mass at two different radii, thus providing a good estimate of the mass profile in between. This result supports universal profiles and explains why single-model approaches can give conflicting results. The mass map itself is elongated in the NW-SE direction, like the galaxy distribution. An overdensity in both mass and light is also apparent to the SE, which suggests meso-structure.