The ROSAT deep survey

VII. RX J105343+5735: A massive cluster at 1.263

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

Corresponding author: D. Thompson, djt@mop.caltech.edu

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 () with colors typical of elliptical galaxies at . 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 Hα emission line at 1.485 microns, yielding a redshift of 1.263. The [Oii] λ3727 Å line 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 . The system may thus represent a pair of clusters in the process of merging.