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

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Letter to the Editor

A search for clusters at high redshift

II. A proto cluster around a radio galaxy at [FORMULA]

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 7

1 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


VLT 1 spectroscopic observations of Ly[FORMULA] -excess objects in the field of the clumpy radio galaxy 1138-262 at [FORMULA] 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 2.16[FORMULA]0.02, 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 [FORMULA] km s-1 and [FORMULA] 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 [FORMULA]9 and [FORMULA]3 [FORMULA] 1013 [FORMULA] respectively, implying a total mass for the structure of more than 1014 [FORMULA]. 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