Studying Cosmic Evolution with the XMM-Newton Distant Cluster Project: X-ray Luminous Galaxy Clusters at z>~1 and their Galaxy Populations

TL;DR

This study uses X-ray and optical/infrared observations to identify and analyze distant galaxy clusters at z>1, revealing insights into galaxy formation, evolution, and the assembly of massive cluster galaxies over cosmic time.

Contribution

It introduces a new Z-H color-based method for confirming and estimating redshifts of distant clusters, enabling studies over a broad redshift range up to z~1.5.

Findings

Early-type galaxies formed at z_f=4.2+-1.1.

Brightest cluster galaxies doubled their stellar mass since z~1.5.

Discovery of over 20 clusters at z>~0.9 from 25% of the sample.

Abstract

Investigating X-ray luminous galaxy clusters at z>~1 provides a fundamental constraint on evolutionary studies of the largest virialized structures in the Universe, the baryonic matter in form of the hot ICM, their galaxy populations, and the effects of Dark Energy. The main aim of this work is to establish the observational foundation for the XMM-Newton Distant Cluster Project (XDCP). This new serendipitous survey is focused on the most distant systems at z>1, based on the selection of extended X-ray sources, their identification as clusters via two-band imaging, and their final spectroscopic confirmation. Almost 1000 extended sources were selected as cluster candidates from the analysis of 80 deg^2 of deep XMM-Newton archival data, of which 75% could be readily identified as systems at z<~0.6. For the remaining 250 distant cluster candidates a new strategy for their confirmation and redshift estimates was adopted, based on Z- and H-band photometry and the observed Z-H red-sequence color of early-type cluster galaxies. From observations of 25% of the sample, more than 20 X-ray clusters were discovered at a photometric redshift of z>~0.9. The new Z-H method has allowed a cluster sample study over an unprecedented redshift baseline of 0.2<~z<~1.5. From a comparison of the observed color evolution of the red-sequence with model predictions, the formation epoch of early-type galaxies could be constrained as z_f=4.2+-1.1, confirming their well-established old age. The preliminary investigation of the H-band luminosity evolution of 63 BCGs provides for the first time direct observational indications that the most massive cluster galaxies have doubled their stellar mass since z~1.5. The finding that BCGs were assembled in the last 9Gyr is now in qualitative agreement with the latest simulations.