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Astron. Astrophys. 344, 393-401 (1999)

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Far-UV and deep surveys: bursting dwarfs versus normal galaxies

Michel Fioc 1,2 and Brigitte Rocca-Volmerange 1,3

1 Institut d'Astrophysique de Paris, CNRS, 98 bis Bd Arago, F-75014 Paris, France
2 NASA/Goddard Space Flight Center, Code 685, Greenbelt, MD 20771, USA
3 Institut d'Astrophysique Spatiale, Bât. 121, Université Paris XI, F-91405 Orsay, France

Received 31 July 1998 / Accepted 18 January 1999


Galaxy counts from bright ultraviolet (UV) and deep optical spectroscopic surveys have revealed an unexpectedly large number of very blue galaxies (vBG). The colors and luminosities of these objects indicate that they are dwarf galaxies undergoing bursts of star formation. We use a galaxy evolution model (pégase, Fioc & Rocca-Volmerange 1997, hereafter FRV) to describe this population as galaxies undergoing cyclical bursts of star formation, thereby determining the luminosity function (LF) of these galaxies.

When these bursting galaxies are added to normally evolving populations, the combination reproduces the UV number counts, color distributions and deep optical redshift distributions fairly well. Optical (including the Hubble Deep Field) and near-infrared number counts are fitted assuming an open or a flat, [FORMULA]-dominated, Universe. The high amplitude of the angular correlation function of very blue galaxies discovered by Landy et al. (1996) is also recovered in this modelling.

The number of bursting galaxies is only a small fraction of the total number of galaxies at optical and near-infrared wavelengths, even at faintest magnitudes. In our evolution modelling, normal galaxies explain most of the blue excess in a low-[FORMULA] Universe. The problem of the blue excess remains in a flat Universe without a cosmological constant.

Key words: galaxies: evolution – galaxies: luminosity function, mass function – galaxies: starburst – cosmology: miscellaneous – ultraviolet: galaxies

Send offprint requests to: Michel Fioc

Correspondence to: fioc@iap.fr

© European Southern Observatory (ESO) 1999

Online publication: March 18, 1999