A SPECTROSCOPICALLY CONFIRMED X-RAY CLUSTER AT z = 1.62 WITH A POSSIBLE COMPANION IN THE SUBARU/ XMM-NEWTON DEEP FIELD

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 4.5σ 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 1.5σ, 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 +0.1 −0.2 Gyr with a mass of 2.5 +0.2 −0.1 × 10 11 M ☉ . 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.