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Astron. Astrophys. 340, L27-L30 (1998)


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Letter to the Editor

The ROSAT Deep Survey

IV. A distant lensing cluster of galaxies with a bright arc

G. Hasinger 1, R. Giacconi 2, J.E. Gunn 3, I. Lehmann 1, M. Schmidt 4, D.P. Schneider 5, J. Trümper 6, J. Wambsganss 1, D. Woods 1 and G. Zamorani 7

1 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
2 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85740 Garching bei München, Germany
3 Princeton University Observatory, Princeton, NJ 08540, USA
4 California Institute of Technology, Pasadena, CA 91125, USA
5 Pennsylvania State University, University Park, PA 16802, USA
6 Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, D-85740 Garching bei München, Germany
7 Osservatorio Astronomico, via Zamboni 33, I-40126 Bologna, Italy

Received 16 September 1998 / Accepted 21 October 1998

Abstract

An unusual double-lobed extended X-ray source (RX J105343+5735) is detected in the ROSAT ultra-deep HRI image of the Lockman Hole. The angular size of the source is [FORMULA] arcmin2 and its X-ray flux is [FORMULA] erg cm-2 s-1. R-band imaging from the Keck telescope revealed a marginal excess of galaxies brighter than R=24.5, but Keck LRIS spectroscopy of 24 objects around the X-ray centroid did not yield a significant number of concordant redshifts. The brightest galaxy close to the centre of the eastern emission peak appears to be a gravitationally lensed arc at z=2.570, suggesting that the X-ray object is associated with the lens, most likely a cluster of galaxies. Based on a comparison of lensing surface mass density, X-ray luminosity, morphology and galaxy magnitudes with clusters of known distance, we argue that RX J105343+5735 is a cluster at a redshift around 1. Future X-ray, ground-based optical/NIR and high resolution HST observations of the system will be able to clarify the nature of the object.

Key words: galaxies: intergalactic medium – cosmology: dark matter, gravitational lensing – X-rays: galaxies

Send offprint requests to: G. Hasinger

© European Southern Observatory (ESO) 1998

Online publication: November 9, 1998

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