Identification of active galaxies behind the Coma cluster of galaxies

C Ledoux (1) , D. Valls-Gabaud (1) , H. Reboul (2) , D. Engels (3) , P. Petitjean (4, 5) , O. Moreau (6, 7)

1 ObAS - Observatoire astronomique de Strasbourg
2 GRAAL - Groupe de Recherche en Astronomie et Astrophysique du Languedoc
3 Hamburger Sternwarte/Hamburg Observatory
4 IAP - Institut d'Astrophysique de Paris
5 DAEC - Departement d'Astrophysique Extragalactique et de Cosmologie
6 LAL - Laboratoire d'Astronomie de Lille
7 Observatoire de Paris

We describe the results of an efficient survey to identify bright B < ∼ 18 active galactic nuclei (AGN) within ≈ 4 • (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-α 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.

Mots clés: galaxies: Seyfert; galaxies: starburst; quasars: absorption lines; quasars: general; techniques: spectroscopic; surveys

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]

C Ledoux, D. Valls-Gabaud, H. Reboul, D. Engels, P. Petitjean, et al.. Identification of active galaxies behind the Coma cluster of galaxies. Astronomy and Astrophysics Supplement Series, 1999, 138, pp.109-117. ⟨10.1051/aas:1999266⟩. ⟨hal-02160086⟩