Evidence for line-of-sight structure in a comparison of X-ray and optical observations of the high-redshift cluster RCS043938-2904.7

TL;DR

This study uses X-ray and optical data to investigate a high-redshift galaxy cluster, revealing complex structure and potential line-of-sight superposition affecting mass estimates.

Contribution

It provides evidence for line-of-sight structure in a high-redshift cluster, combining X-ray and optical observations to refine mass estimates and understand cluster composition.

Findings

X-ray and optical mass estimates differ significantly for the single cluster assumption.

Optical spectroscopy indicates the presence of two close components, possibly physically associated.

Modeling suggests the cluster is a superposition of two components, aligning mass estimates with expectations.

Abstract

We present new Chandra observations of a high redshift (z~1) galaxy cluster discovered in the Red-Sequence Cluster Survey (RCS): RCS043938-2904.7. X-ray luminosity measurements and mass estimates are consistent with L_X-T_X and M_delta-T_X relationships obtained from low-redshift data. Assuming a single cluster, X-ray mass estimates are a factor of ~10-100 below the red-sequence optical richness mass estimate. Optical spectroscopy reveals that this cluster comprises two components which are close enough to perhaps be physically associated. We present simple modeling of this two-component system which then yields an X-ray mass and optical richness consistent with expectations from statistical samples of lower redshift clusters. An unexpectedly high gas mass fraction is measured assuming a single cluster, which independently supports this interpretation. Additional observations will be necessary to confirm the excess gas mass fraction and to constrain the mass distribution.