Star formation in the intragroup medium and other diagnostics of the evolutionary stages of compact groups of galaxies*
Universidade de São Paulo, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Departamento de Astronomia, São Paulo, Brazil e-mail: firstname.lastname@example.org
2 Laboratoire d'Astrophysique de Marseille, OAMP, Université de Provence & CNRS, 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France
3 Observational Cosmology Laboratory, Code 665, Goddard Space Flight Center, Greenbelt, MD 20771, USA
4 Catholic University of America, Washington, DC 20064, USA
5 Johns Hopkins University, Baltimore, MD 21218, USA
6 Laboratorio de Astrofisica Teorica e Observacional, Universidade Estadual de Santa Cruz, Brazil
7 Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 14 avenue Edouard Belin, 31400 Toulouse, France
8 Instituto de Astrofisica de Andalucia (CSIC), Camino Bajo de Huetor 50, 18008 Granada, Spain
Accepted: 12 August 2009
Context. Compact groups of galaxies are entities that have high densities of galaxies and serve as laboratories to study galaxy interactions, intergalactic star formation and galaxy evolution.
Aims. The main goal of this study is to search for young objects in the intragroup medium of seven compact groups of galaxies: HCG 2, 7, 22, 23, 92, 100 and NGC 92 as well as to evaluate the stage of interaction of each group.
Methods. We used Fabry-Perot velocity fields and rotation curves together with GALEX NUV and FUV images and optical R-band and HI maps.
Results. (i) HCG 7 and HCG 23 are in early stages of interaction; (ii) HCG 2 and HCG 22 are mildly interacting; and (iii) HCG 92, HCG 100 and NGC 92 are in late stages of evolution. We find that all three evolved groups contain populations of young blue objects in the intragroup medium, consistent with ages < 100 Myr, of which several are younger than <10 Myr. We also report the discovery of a tidal dwarf galaxy candidate in the tail of NGC 92. These three groups, besides containing galaxies that have peculiar velocity fields, also show extended HI tails.
Conclusions. Our results indicate that the advanced stage of evolution of a group, together with the presence of intragroup HI clouds, may lead to star formation in the intragroup medium. A table containing all intergalactic HII regions and tidal dwarf galaxies confirmed to date is appended.
Key words: galaxies: evolution / galaxies: interactions / galaxies: intergalactic medium / galaxies: kinematics and dynamics
© ESO, 2009