* Astronomy

Title: A Chandra view of the z=1.62 galaxy cluster IRC-0218A
Authors: M. Pierre, N. Clerc, B. Maughan, F. Pacaud, C. Papovich, C. N. A. Willmer

Context: Very few z > 1.5 clusters of galaxies are known. It is important to study the properties of galaxies in these clusters and the ICM and, further, 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: 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 MIR galaxy density. In addition, we detect weak extended emission (2.3{\sigma}) out to a radius of 25" with a flux of ~ 3 10^-15 erg/s/cm2 in the [0.3-2]keV band. Assuming that clusters evolve similarly, we infer a virial mass of M200 =7.7(±3.8)10^13 solar masses. 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 1-2 10^12 solar masses. We provide a detailed account of 28 X-ray point-sources detected in the field.

Read more  (2139kb, PDF)