Spectroscopy of moderately high-redshift RCS-1 clusters

TL;DR

This study presents spectroscopic data for 11 high-redshift galaxy clusters from RCS-1, confirming the accuracy of red-sequence estimates and exploring the relation between optical richness and mass.

Contribution

It provides spectroscopic confirmation of cluster redshifts and examines the correlation between optical richness and dynamical mass at z~0.7-1.0.

Findings

Red-sequence redshift estimates agree well with spectroscopic measurements.

Identified projection effects in some high-redshift systems.

Optical richness correlates with dynamical mass within uncertainties.

Abstract

We present spectroscopic observations of 11 moderately high-redshift (z~0.7- 1.0) clusters from the first Red-Sequence Cluster Survey (RCS-1). We find excellent agreement between the red-sequence estimated redshift and the spectroscopic redshift, with a scatter of 10% at z>0.7. At the high-redshift end (z>~0.9) of the sample, we find two of the systems selected are projections of pairs of comparably rich systems, with red-sequences too close to discriminate in (R-z') colour. In one of these systems, the two components are close enough to be physically associated. For a subsample of clusters with sufficient spectroscopic members, we examine the correlation between B_gcR (optical richness) and the dynamical mass inferred from the velocity dispersion. We find these measurements to be compatible, within the relatively large uncertainties, with the correlation established at lower redshift for the X-ray selected CNOC1 clusters and also for a lower redshift sample of RCS-1 clusters. Confirmation of this and calibration of the scatter in the relation will require larger samples of clusters at these and higher redshifts. [abridged]