Chandra deep observation of XDCP j0044.0-2033, a massive galaxy cluster at z > 1.5

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+1.3-0.9 keV, and a iron abundance ZFe = 0.41-0.26+0.29ZFe_⊙ (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) × 1013 M ⊙. Under the assumption of hydrostatic equilibrium and assuming isothermality within R ext, the total mass is M2500= 1.23-0.27+0.46 × 10 14 M_⊙ 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+0.9 × 10 14 M_⊙ for R500 = 562-37+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