The spectroscopically confirmed X-ray cluster at z=1.62 with a possible companion in the Subaru/XMM-Newton deep field

TL;DR

This paper reports the discovery and confirmation of a galaxy cluster at redshift 1.62 in the Subaru/XMM-Newton deep field, demonstrating the feasibility of detecting high-z clusters via X-ray and near-IR observations.

Contribution

First spectroscopic confirmation of a high-redshift galaxy cluster at z=1.62 with associated X-ray emission, including analysis of galaxy properties and cluster characteristics.

Findings

X-ray detection confirms a gravitationally bound high-z cluster.

Presence of a red sequence indicates mature galaxy populations.

Spectroscopic data suggests galaxies are old with formation redshift z_f=3.

Abstract

We report on a confirmed galaxy cluster at z=1.62. We discovered two concentrations of galaxies at z~1.6 in the Subaru/XMM-Newton deep field based on deep multi-band photometric data. We made a near-IR spectroscopic follow-up observation of them and confirmed several massive galaxies at z=1.62. One of the two is associated with an extended X-ray emission at 4.5 sigma on a scale of 0'.5, which is typical of high-z clusters. The X-ray detection suggests that it is a gravitationally bound system. The other one shows a hint of an X-ray signal, but only at 1.5 sigma, and we obtained only one secure redshift at z=1.62. We are not yet sure if this is a collapsed system. The possible twins exhibit a clear red sequence at K<22 and seem to host relatively few number of faint red galaxies. Massive red galaxies are likely old galaxies -- they have colors consistent with the formation redshift of z_f=3 and a spectral fit of the brightest confirmed member yields an age of 1.8_{-0.2}^{+0.1} Gyr with a mass of 2.5_{-0.1}^{+0.2} x 10^11 M_solar. Our results show that it is feasible to detect clusters at z>1.5 in X-rays and also to perform detailed analysis of galaxies in them with the existing near-IR facilities on large telescopes.