  Galaxy counts from bright ultraviolet (UV) and deep optical spectroscopic
surveys have revealed an unexpectedly large number of very blue galaxies. The
colors and luminosities of these objects indicate that they are dwarf galaxies
undergoing bursts of star formation. We use a galaxy evolution model (PEGASE,
Fioc & Rocca-Volmerange 1997) to describe this population as galaxies
undergoing cyclical bursts of star formation, thereby determining the
luminosity function 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,
Lambda-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-Omega Universe. The problem of the blue excess remains in
a flat Universe without a cosmological constant.

Astrophysics