Astron. Astrophys. Suppl. Ser. 138, 109-117

Identification of active galaxies behind the Coma cluster of galaxies

C. Ledoux¹ - D. Valls-Gabaud¹² - H. Reboul³ - D. Engels⁴ - P. Petitjean⁵⁶ - O. Moreau⁷⁸

Send offprint request: C. Ledoux
(cedric@astro.u-strasbg.fr)

1 - UMR 7550 CNRS, Observatoire Astronomique de Strasbourg, 11 rue de l'Université, F-67000 Strasbourg, France
2 - Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
3 - GRAAL, Université Montpellier II, F-34095 Montpellier Cedex 5, France
4 - Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg, Germany
5 - Institut d'Astrophysique de Paris - CNRS, 98bis Boulevard Arago, F-75014 Paris, France
6 - DAEC, Observatoire de Paris-Meudon, F-92195 Meudon Principal Cedex, France
7 - Laboratoire d'Astronomie de l'Université Lille I, Impasse de l'Observatoire, F-59000 Lille, France
8 - Centre d'Analyse des Images, Observatoire de Paris, 61 avenue de l'Observatoire, F-75014 Paris, France

Received January 12; accepted May 21, 1999

Abstract:

We describe the results of an efficient survey to identify bright active galactic nuclei (AGN) within $\approx 4\hbox{$^\circ$}$ (4.7 h^-1 Mpc projected radius) of the centre of the Coma cluster of galaxies. The candidates have been carefully selected either as unresolved UV-excess objects with no detected proper motion, or from identifications on objective-prism plates including a few ROSAT sources. A global success rate larger than 30% is achieved. Low-resolution spectra are presented for the extragalactic objects identified in the course of the survey: the sample contains 16 emission-line objects, a BL Lac candidate and an elliptical galaxy. The AGNs of this list are unique targets to study the association of the Lyman-$\alpha$ forest with large-scale structures and galactic haloes at low redshift, to search for warm gas within the Coma cluster and nearby filaments, and for optical monitoring to detect the micro-lensing variability produced by the baryonic dark matter in the cluster.

Key words: quasars: general -- quasars: absorption lines -- galaxies: Seyfert -- galaxies: starburst -- techniques: spectroscopic -- surveys