The 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 4.5 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.
