The X-ray brightest clusters of galaxies from the Massive Cluster Survey

TL;DR

This paper presents a complete sample of the brightest X-ray galaxy clusters from the MACS survey, demonstrating the effectiveness of X-ray selection in identifying massive clusters at redshifts 0.3 to 0.5.

Contribution

It introduces a new, complete sample of 34 luminous galaxy clusters from MACS, including many new discoveries, and validates X-ray selection for finding massive clusters at intermediate redshifts.

Findings

Median X-ray luminosity of clusters is 1.3x10^45 erg/s.

Two-thirds of the clusters are newly discovered.

Wide morphological diversity observed among clusters.

Abstract

We present a statistically complete sample of very X-ray luminous galaxy clusters detected in the MAssive Cluster Survey (MACS). This second MACS release comprises all 34 MACS clusters with nominal X-ray fluxes in excess of 2x10^(-12) erg/s/cm^2 (0.1-2.4 keV) in the ROSAT Bright Source Catalogue; two thirds of them are new discoveries. Extending over the redshift range from 0.3 to 0.5, this subset complements the complete sample of the 12 most distant MACS clusters (z>0.5) published in 2007 and further exemplifies the efficacy of X-ray selection for the compilation of samples of intrinsically massive galaxy clusters. Extensive follow-up observations with Chandra/ACIS led to three additional MACS cluster candidates being eliminated as (predominantly) X-ray point sources. For another four clusters --- which, however, remain in our sample of 34 --- the point-source contamination was found to be about 50%. The median X-ray luminosity of 1.3x10^45 erg/s (0.1-2.4 keV, Chandra, within r_500) of the clusters in this subsample demonstrates the power of the MACS survey strategy to find the most extreme and rarest clusters out to significant redshift. A comparison of the optical and X-ray data for all clusters in this release finds a wide range of morphologies with no obvious bias in favour of either relaxed or merging systems.