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A mature cluster with X-ray emission at $z$=2.07

Abstract : We report evidence of a fully established galaxy cluster at $z$=2.07, consisting of a $\sim$ 20$\sigma$ overdensity of red, compact spheroidal galaxies spatially coinciding with extended X-ray emission detected with XMM-Newton. We use VLT VIMOS and FORS2 spectra and deep Subaru, VLT and Spitzer imaging to estimate the redshift of the structure from a prominent $z$=2.07 spectroscopic redshift spike of emission-line galaxies, concordant with the accurate 12-band photometric redshifts of the red galaxies. Using NICMOS and Keck AO observations, we find that the red galaxies have elliptical morphologies and compact cores. While they do not form a tight red sequence, their colours are consistent with that of a $\geq$1.3 Gyr population observed at $z \sim$2.1. From an X-ray luminosity of 7.2 x 10$^{43}$ erg $s^{-1}$ and the stellar mass content of the red galaxy population, we estimate a halo mass of 5.3$-$8x10$^{13}$ M$\odot$, comparable to the nearby Virgo cluster. These properties imply that this structure could be the most distant, mature cluster known to date and that X-ray luminous, elliptical-dominated clusters are already forming at substantially earlier epochs than previously known.
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R. Gobat, Emanuele Daddi, M. Onodera, A. Finoguenov, A. Renzini, et al.. A mature cluster with X-ray emission at $z$=2.07. Astronomy and Astrophysics - A&A, EDP Sciences, 2011, 526, pp.A133. ⟨10.1051/0004-6361/201016084⟩. ⟨cea-01001650⟩



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