* Astronomy

Title: Discovery of a massive X-ray luminous galaxy cluster at z=1.579
Authors: Joana S. Santos (1), Rene Fassbender (2), Alessandro Nastasi (2), Hans Böhringer (2), Piero Rosati (3), Robert Suhada (2), Daniele Pierini (2), Mario Nonino (4), Martin Muehlegger (2), Hernan Quintana (5), Axel D. Schwope (6), Georg Lamer (6), Arjen de Hoon (6), Veronica Strazzullo (7) ((1) ESAC/ESA, (2) MPE, (3) ESO, (4) INAF-Trieste, (5) PUC-Chile, (6) AIP, (7) CEA-Saclay)

We report on the discovery of a very distant galaxy cluster serendipitously detected in the archive of the XMM-Newton mission, within the scope of the XMM-Newton Distant Cluster Project (XDCP). XMMUJ0044.0-2033 was detected at a high significance level (5sigma) as a compact, but significantly extended source in the X-ray data, with a soft-band flux f(r<40")=(1.5±0.3)x10^(-14) erg/s/cm². Optical/NIR follow-up observations confirmed the presence of an overdensity of red galaxies matching the X-ray emission. The cluster was spectroscopically confirmed to be at z=1.579 using ground-based VLT/FORS2 spectroscopy. The analysis of the I-H colour-magnitude diagram shows a sequence of red galaxies with a colour range [3.7 < I-H < 4.6] within 1' from the cluster X-ray emission peak. However, the three spectroscopic members (all with complex morphology) have significantly bluer colours relative to the observed red-sequence. In addition, two of the three cluster members have [OII] emission, indicative of on-going star formation. Using the spectroscopic redshift we estimated the X-ray bolometric luminosity, Lbol = 5.8x10^44 erg/s, implying a massive galaxy cluster. This places XMMU J0044.0-2033 at the forefront of massive distant clusters, closing the gap between lower redshift systems and recently discovered proto- and low-mass clusters at z >1.6.

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