Galaxies spatially coincident with the JKCS041 X-ray emission display a red sequence at z~2.2

Abstract

New deep z'-J data readly show a narrow red sequence co-centered with, and similary concentrated to, the extended X-ray emission of the cluster of galaxies JKCS041. The JKCS041 red sequence is 0.32+/-0.06 mag redder in z'-J than the red sequence of the zspec=1.62 IRC0218A cluster, putting JKCS041 at z<<1.62. The colour difference of the two red sequences gives a red-sequence based redshift of z=2.20+/-0.11 for JKCS041, where the uncertainty accounts for uncertainties in stellar synthesis population models, in photometric calibration and in the red sequence colour of both JKCS041 and IRC0218A clusters.

Mem SAIt, in press. Press-release and additional material related to this paper and to arXiv:1012.1951 (A&A 526, A11) can be found at http://www.brera.mi.astro.it/%7Eandreon/JKCS041/JKCS041.html