An X-Ray-Selected Galaxy Cluster at Z = 1.26
Abstract
We report the discovery of an X-ray-luminous galaxy cluster at z=1.26. RX J0848.9+4452 was selected as an X-ray cluster candidate in the ROSAT Deep Cluster Survey on the basis of its spatial extent. Deep optical and near-IR imaging have revealed a galaxy overdensity around the peak of the X-ray emission, with a significant excess of red objects with J-K colors typical of elliptical galaxies at z>1. Spectroscopic observations at the Keck II Telescope have secured six galaxy redshifts in the range 1.257<z<1.267 (<z>=1.261) within a 35" radius around the peak X-ray emission. This system lies only 4.2‧ away (5.0 h^-1_50 comoving Mpc, q_0=0.5) from the galaxy cluster ClG J0848+4453, which was identified at z=1.273 in a near-IR field galaxy survey and is also known to be X-ray luminous. Assuming that the X-ray emission is entirely due to hot intracluster gas, both these systems have similar rest-frame luminosities L_X~1x10^44 ergs s^-1 (0.5-2.0 keV band). In combination with our spectrophotometric data for the entire 30 arcmin^2 field, this suggests the presence of a superstructure consisting of two collapsed, possibly virialized, clusters, the first detected to date at z>1. Based in part on observations obtained at the W. M. Keck Observatory.
- Publication:
-
The Astronomical Journal
- Pub Date:
- July 1999
- DOI:
- 10.1086/300934
- arXiv:
- arXiv:astro-ph/9903381
- Bibcode:
- 1999AJ....118...76R
- Keywords:
-
- GALAXIES: CLUSTERS: GENERAL;
- GALAXIES: EVOLUTION;
- GALAXIES: FORMATION;
- X-RAYS;
- Astrophysics
- E-Print:
- To appear in The Astronomical Journal, 24 pages, 8 figures, 1 color jpg plate (fig.7), see http://www.eso.org/~prosati/lynx/plate_fig7.jpg