Chandra and optical/IR observations of CXO J1415.2+3610, a massive, newly discovered galaxy cluster at z ∼ 1.5

Aims. We report the discovery of CXO J1415.2+3610, a distant (z similar to 1.5) galaxy cluster serendipitously detected as an extended source with a very high significance level (S/N similar to 11) 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. Methods. We perform an X-ray spectral fit of the extended emission of the intracluster medium (ICM) with Xspec assuming a single-temperature thermal me\l model. We use optical and infrared (IR) observations from Subaru-Suprime (BVRiz), Moircs (JK(s)), and Spitzer-IRAC (3.6 mu m) to confirm the presence of an overdensity of red galaxies matching the X-ray extended emission. We use optical and IR data to investigate the color-magnitude relation of the candidate member galaxies. Results. From a preliminary X-ray spectral analysis, 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 zX = 1.46 +/- 0.025. Our X-ray redshift measurement is supported by the optical and IR data. 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 fitting is z(phot) = 1.52 +/- 0.06. After fixing the redshift to z = 1.46, we perform the final spectral analysis and measure the average gas temperature Wwith a 20% error, kT = 5.8(-1.0)(+1.2) keV, and the Fe abundance ZFe = 1.3(-0.5)(+0.8) Z(circle dot). We fit the background-subtracted surface brightness with a single beta-model out to 35 arcsec (the maximum radius where the X-ray emission is detected), and derive the deprojected electron density profile. The ICM mass is 1.09(-0.2)(+0.3) x 10(13) M-circle dot within 300 kpc. Under the assumption of hydrostatic equilibrium, the total mass is M-2500 = 8.6(-1.7)(+2.1) x 10(13) M-circle dot 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) M-circle dot 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.