Chandra X-ray Observations of the 0.6 < z < 1.1 Red-Sequence Cluster Survey Sample

TL;DR

This study uses Chandra X-ray observations to analyze 13 high-redshift galaxy clusters from the Red-sequence Cluster Survey, revealing their properties, scaling relations, and discrepancies with lower-redshift samples, suggesting complex baryonic processes.

Contribution

First detailed X-ray analysis of optically-selected clusters at 0.6<z<1.1, examining their scaling relations and baryonic content compared to lower-redshift samples.

Findings

RCS clusters are consistent with self-similar scaling expectations.

High-z RCS clusters have lower X-ray luminosity for a given temperature compared to lower-z samples.

Gas mass fractions within R(2500) are about half of expectations, indicating elevated central entropy.

Abstract

We present the results of Chandra observations of 13 optically-selected clusters with 0.6<z< 1.1, discovered via the Red-sequence Cluster Survey (RCS). All but one are detected at S/N>3; though 3 were not observed long enough to support detailed analysis. Surface brightness profiles are fit to beta-models. Integrated spectra are extracted within R(2500), and Tx and Lx information is obtained. We derive gas and total masses within R(2500) and R(500). Cosmologically corrected scaling relations are investigated, and we find the RCS clusters to be consistent with self-similar scaling expectations. However discrepancies exist between the RCS sample and lower-z X-ray selected samples for relationships involving Lx, with the higher-z RCS clusters having lower Lx for a given Tx. In addition, we find that gas mass fractions within R(2500) for the high-z RCS sample are lower than expected by a factor of ~2. This suggests that the central entropy of these high-z objects has been elevated by processes such as pre-heating, mergers, and/or AGN outbursts, that their gas is still infalling, or that they contain comparatively more baryonic matter in the form of stars. Finally, relationships between red-sequence optical richness (Bgc) and X-ray properties are fit to the data. For systems with measured Tx, we find that optical richness correlates with both Tx and mass, having a scatter of ~30% with mass for both X-ray and optically-selected clusters. However we also find that X-ray luminosity is not well correlated with richness, and that several of our sample appear to be significantly X-ray faint.