2015ApJ...799...93T

We report the analysis of the Chandra observation of XDCP J0044.0-2033, a massive, distant (z = 1.579) galaxy cluster discovered in the XDCP survey. The total exposure time of 380 ks with Chandra ACIS-S provides the deepest X-ray observation currently achieved on a massive, high-redshift cluster. Extended emission from the intra cluster medium (ICM) is detected at a very high significance level (S/N ∼ 20) on a circular region with a 44'' radius, corresponding to R_ext= 375 kpc at the cluster redshift. We perform an X-ray spectral fit of the ICM emission modeling the spectrum with a single-temperature thermal mekal model. Our analysis provides a global temperature kT = 6.7_–0.9^+1.3 keV, and a iron abundance Z_Fe = 0.41_–0.26^+0.29 Z_Fe☉ (error bars correspond to 1σ). We fit the background-subtracted surface brightness profile with a single β-model out to 44'', finding a rather flat profile with no hints of a cool core. We derive the deprojected electron density profile and compute the ICM mass within the extraction radius R_ext= 375 kpc to be M_ICM(r < R_ext) = (1.48±0.20)x10¹³ M_☉. Under the assumption of hydrostatic equilibrium and assuming isothermality within R_ext, the total mass is M₂₅₀₀ = 1.23_–0.27^+0.46 x 10¹⁴M_☉ for R₂₅₀₀ = 240_–20⁺³⁰ kpc. Extrapolating the profile at radii larger than the extraction radius R_ext we find M₅₀₀ = 3.2_–0.6^+0.9x 10¹⁴M_☉ for R₅₀₀ = 526_–37⁺⁵⁰ kpc. This analysis establishes the existence of virialized, massive galaxy clusters at redshift z ∼ 1.6, paving the way to the investigation of the progenitors of the most massive clusters today. Given its mass and the XDCP survey volume, XDCP J0044.0-2033 does not create significant tension with the WMAP-7 ΛCDM cosmology.