Planck Early Results XXVI: Detection with Planck and confirmation by XMM-Newton of PLCK G266.6-27.3, an exceptionally X-ray luminous and massive galaxy cluster at z~1

TL;DR

This paper reports the discovery and confirmation of an exceptionally luminous and massive galaxy cluster at redshift ~1, demonstrating Planck's effectiveness in detecting high-redshift, high-mass clusters for studying cosmic evolution.

Contribution

It provides the first validation of a high-redshift galaxy cluster detected by Planck using XMM-Newton, including precise measurements of its redshift and mass.

Findings

Confirmed a high-redshift, massive galaxy cluster with X-ray luminosity comparable to the most luminous known at z > 0.5.

Measured the cluster's redshift as z = 0.94 +/- 0.02.

Estimated the cluster mass to be approximately 7.8 x 10^14 solar masses.

Abstract

We present first results on PLCK G266.6-27.3, a galaxy cluster candidate detected at a signal-to-noise ratio of 5 in the Planck All Sky survey. An XMM-Newton validation observation has allowed us to confirm that the candidate is a bona fide galaxy cluster. With these X-ray data we measure an accurate redshift, z = 0.94 +/- 0.02, and estimate the cluster mass to be M_500 = (7.8 +/- 0.8)e+14 solar masses. PLCK G266.6-27.3 is an exceptional system: its luminosity of L_X(0.5-2.0 keV)=(1.4 +/- 0.05)e+45 erg/s, equals that of the two most luminous known clusters in the z > 0.5 universe, and it is one of the most massive clusters at z~1. Moreover, unlike the majority of high-redshift clusters, PLCK G266.6-27.3 appears to be highly relaxed. This observation confirms Planck's capability of detecting high-redshift, high-mass clusters, and opens the way to the systematic study of population evolution in the exponential tail of the mass function.