* Astronomy

Title: Chandra and optical/IR observations of CXOJ1415.2+3610, a massive, newly discovered galaxy cluster at z~1.5
Authors: P. Tozzi, J.S. Santos, M. Nonino, P. Rosati, S. Borgani, B. Sartoris, B. Altieri, M. Sanchez-Portal

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 Intra Cluster 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 ±0.025. The analysis of the z-3.6\mu m colour-magnitude diagram shows a well defined sequence of red galaxies within 1' from the cluster X-ray emission peak with a colour range [5 < z-3.6 \mu m < 6]. The photometric redshift obtained by SED fitting is z_phot=1.47 ±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} x 10^{13} solar masses within 300 kpc. The total mass is M_{2500}= 8.6_{-1.7}^{+2.1} x 10 ^{13} solar masses for R_{2500}=(220±55) kpc. Extrapolating the profile at larger radii we find M_{500}= 2.1_{-0.5}^{+0.7} x  10 ^{14} solar masses for R_{500} = 510_{-50}^{+55} kpc. This analysis establishes CXOJ1415.2+3610 as one of the best characterised distant galaxy clusters known to date.

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