A Chandra view of the z = 1.62 galaxy cluster IRC-0218A

¹ Laboratoire AIM, CEA/DSM/IRFU/SAp, CEA Saclay, 91191 Gif-sur-Yvette, France
e-mail: mpierre@cea.fr
² HH Wills Physics Laboratory, University of Bristol, UK
³ Argelander-Institut für Astronomie, University of Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁴ Texas A&M, University Department of Physics and Astronomy, College Station, TX 77843-4242, USA
⁵ Steward Observatory, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721, USA

Received: 28 September 2011
Accepted: 13 December 2011

Abstract

Context. Very few z > 1.5 clusters of galaxies are currently known. It is important to study the properties of galaxies in these clusters and the intra-cluster medium and, furthermore, to cross-check the reliability of the various mass estimates. This will help to clarify the process of structure formation and how distant clusters may be used to constrain cosmology.

Aims. We present a 84 ks Chandra observation of IRC-0218A, a cluster of galaxies inferred by the presence of a galaxy overdensity in the infrared at a redshift of 1.62 and associated with some XMM emission.

Methods. We performed a spatial analysis of the Chandra X-ray photon distribution.

Results. The Chandra observation of IRC-0218A appears to be entirely dominated by a point source located at the centroid of the mid-infrared galaxy density. In addition, we detected weak extended emission (2.3σ) out to a radius of 25′′ with a flux of  ~3 × 10^-15 erg   s^-1   cm^-2 in the [0.3–2] keV band. Assuming that clusters evolve similarly, we infer a virial mass of M₂₀₀ = 7.7( ± 3.8) × 10¹³   M_⊙. This is marginally compatible with our current estimate of the cluster dynamical mass (based on 10 redshifts), although there is no evidence that the galaxy peculiar velocities correspond to the motions of a virialized structure. The stellar mass enclosed in the inferred X-ray virial radius is estimated to be 1–2 × 10¹²   M_⊙. We provide a detailed account of 28 X-ray point sources detected in the field.