Astron. Astrophys. 361, L25-L28 (2000)

Letter to the Editor

A search for clusters at high redshift

II. A proto cluster around a radio galaxy at

L. Pentericci ^1,2, J.D. Kurk ², H.J.A Röttgering ², G.K. Miley ², W. van Breugel ³, C.L. Carilli ⁴, H. Ford ⁵, T. Heckman ⁵, P. McCarthy ⁶ and A. Moorwood <sup>7

1</sup> Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany
² Sterrewacht Leiden, P.O. Box 9513, 2300 RA, Leiden, The Netherlands
³ Lawrence Livermore National Laboratory, P.O. Box 808, Livermore CA, 94550, USA
⁴ NRAO, P.O. Box 0, Socorro NM, 87801, USA
⁵ Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore MD, 21218-2686, USA
⁶ The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena CA, 91101, USA
⁷ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748, Garching bei München, Germany

Received 18 July 2000 / Accepted 14 August 2000

Abstract

VLT ¹ spectroscopic observations of Ly -excess objects in the field of the clumpy radio galaxy 1138-262 at have led to the discovery of 14 galaxies and one QSO at approximately the same distance as the radio galaxy. All galaxies have redshifts in the range 2.160.02, centered around the redshift of the radio galaxy, and are within a projected physical distance of 1.5 Mpc from it. The velocity distribution suggests that there are two galaxy subgroups having velocity dispersions of km s^-1 and km s^-1 and a relative velocity of 1800 km s^-1. If these are virialized structures, the estimated dynamical masses for the subgroups are 9 and 3 10¹³  respectively, implying a total mass for the structure of more than 10¹⁴ . The new observations, together with previous results, suggest that the structure of galaxies around 1138-262 is likely to be a forming cluster.

Key words: galaxies: active galaxies: clusters: general galaxies: evolution cosmology: observations cosmology: early Universe cosmology: large-scale structure of Universe

Send offprint requests to: L. Pentericci (laura@mpia-hd.mpg.de)

© European Southern Observatory (ESO) 2000

Online publication: October 2, 2000

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