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Astron. Astrophys. 334, 765-769 (1998)


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Deep probing of the Coma cluster *

C. Adami 1, R.C. Nichol 2, A. Mazure 1, F. Durret 3, 4, B. Holden 5 and C. Lobo 3, 6

1 IGRAP, Laboratoire d'Astronomie Spatiale, CNRS, Traverse du Siphon, Les Trois Lucs, F-13012 Marseille, France
2 Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA
3 Institut d'Astrophysique, CNRS, Université Pierre et Marie Curie, 98bis Bd Arago, F-75014 Paris, France
4 DAEC, Observatoire de Paris, Université Paris VII, CNRS (UA 173), F-92195 Meudon Cedex, France
5 Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Avenue, Chicago, IL 60637, USA
6 Osservatorio Astronomico di Brera, via Brera 28, I-20121 Milano, Italy

Received 28 October 1997 / Accepted 6 March 1998

Abstract

As a continuation of our study of the faint galaxy luminosity function in the Coma cluster of galaxies, we report here on the first spectroscopic observations of very faint galaxies (R [FORMULA] 21.5) in the direction of the core of this cluster. Out of these 34 galaxies, only one may have a redshift consistent with Coma, all others are background objects. The predicted number of Coma galaxies is 6.7 [FORMULA] 6.0, according to Bernstein et al. (1995, B95). If we add the 17 galaxies observed by Secker (1997), we end up with 5 galaxies belonging to Coma, while the expected number is 16.0 [FORMULA] 11.0 according to B95. Notice that these two independent surveys lead to the same results. Although the observations and predicted values agree within the error, such results raise into question the validity of statistical subtraction of background objects commonly used to derive cluster luminosity functions (e.g. B95). More spectroscopic observations in this cluster and others are therefore urgently needed.

As a by-product, we report on the discovery of a physical structure at a redshift z [FORMULA] 0.5.

Key words: cluster: individual: Coma cluster – clusters: general – galaxies: catalogs – galaxies: distances and redshifts – galaxies: luminosity function, mass function

* Based on observations collected at the Canada France Hawaii telescope, operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique of France, and the University of Hawaii

Send offprint requests to: C. Adami, adami@astrsp-mrs.fr

© European Southern Observatory (ESO) 1998

Online publication: June 2, 1998

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