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Issue A&A
Volume 377, Number 3, October III 2001
Page(s) 778 - 783
Section Extragalactic astronomy
DOI 10.1051/0004-6361:20011049



A&A 377, 778-783 (2001)
DOI: 10.1051/0004-6361:20011049

The ROSAT deep survey

VII. RX J105343+5735: A massive cluster at z= 1.263
D. Thompson1, L. Pozzetti2, G. Hasinger3, I. Lehmann3, 4, M. Schmidt1, B. T. Soifer1, 5, G. Szokoly3, G. Wilson6 and G. Zamorani2

1  Palomar Observatory, California Institute of Technology, MS 320-47 Pasadena, CA 91125, USA
2  Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127 Bologna, Italy
3  Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Postdam, Germany
4  Department of Astronomy & Astrophysics, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA 16802, USA
5  SIRTF Science Center, California Institute of Technology, Pasadena, CA 91125, USA
6  Physics Department, Brown University 182 Hope Street Providence, RI 02912, USA

(Received 14 May 2001 / Accepted 16 July 2001)

Abstract
The eastern lobe of the unusual double-lobed extended X-ray source RX J105343+5735 is confirmed to be a massive cluster at high redshift. Deep optical and near-infrared imaging show an overdensity of galaxies in both X-ray lobes, including a significant excess of red galaxies (R-K> 5.3) with colors typical of elliptical galaxies at z> 1. We have used new photometry to place better constraints on the redshifts of the cluster galaxies. A Keck NIRSPEC spectrum of one of the bright central galaxies in the eastern lobe shows a narrow H$\alpha$ emission line at 1.485 microns, yielding a redshift of 1.263. The [OII] $\lambda$3727 Åline from the gravitationally lensed arc is also detected, giving a redshift of 2.577 for the lensed galaxy and confirming prior measurements. The improbability of chance alignment and similarity of colors for the galaxies in the two X-ray lobes are consistent with the western lobe also being at z=1.26. The system may thus represent a pair of clusters in the process of merging.


Key words: galaxies: clusters, distances and redshifts -- cosmology: observations, gravitational lensing -- infrared: galaxies -- X-rays: galaxies

Offprint request: D. Thompson, djt@mop.caltech.edu

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© ESO 2001


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