Chandra and optical/IR observations of CXOJ1415.2+3610, a massive, newly
  discovered galaxy cluster at z~1.5
  (Abridged) We report the discovery of CXO J1415.2+3610, a distant (z~1.5)
galaxy cluster serendipitously detected in a deep, high-resolution Chandra
observation targeted to study the cluster WARP J1415.1+3612 at z=1.03. This is
the highest-z cluster discovered with Chandra so far. Moreover, the total
exposure time of 280 ks with ACIS-S provides the deepest X-ray observation
currently achieved on a cluster at z>1.5. We perform an X-ray spectral fit of
the extended emission of the intracluster medium (ICM) with XSPEC, and we
detect at a 99.5% confidence level the rest frame 6.7-6.9 keV Iron K_\alpha
line complex, from which we obtain z_X=1.46\pm0.025. The analysis of the
z-3.6\mu m color-magnitude diagram shows a well defined sequence of red
galaxies within 1' from the cluster X-ray emission peak with a color range [5 <
z-3.6 \mu m < 6]. The photometric redshift obtained by spectral energy
distribution (SED) fitting is z_phot=1.47\pm 0.25. After fixing the redshift to
z=1.46, we perform the final spectral analysis and measure the average gas
temperature with a 20% error, kT=5.8^{+1.2}_{-1.0} keV, and the Fe abundance
Z_Fe = 1.3_{-0.5}^{+0.8}Z_\odot. We fit the background subtracted surface
brightness with a single beta--model out to 35" and derive the deprojected
electron density profile. The ICM mass is 1.09_{-0.2}^{+0.3}\times 10^{13}
M_\odot within 300 kpc. The total mass is M_{2500}= 8.6_{-1.7}^{+2.1} \times 10
^{13} M_\odot for R_{2500}=(220\pm 55) kpc. Extrapolating the profile at larger
radii we find M_{500}= 2.1_{-0.5}^{+0.7} \times 10 ^{14} M_\odot for R_{500} =
510_{-50}^{+55}$ kpc. This analysis establishes CXOJ1415.2+3610 as one of the
best characterized distant galaxy clusters based on X-ray data alone.
