PEGASE: a UV to NIR spectral evolution model of galaxies. Application to the calibration of bright galaxy counts.

PEGASE (Projet d'Etude des GAlaxies par Synthese Evolutive, in French) is a new spectrophotometric evolution model for starbursts and evolved galaxies of the Hubble sequence. Its main originality is the extension to the near-infrared (NIR) of the atlas of synthetic spectra of Rocca-Volmerange & Guiderdoni (1988A&AS...75...93R) with a revised stellar library including cold star parameters and stellar tracks extended to the thermally-pulsing regime of the asymptotic giant branch (TP-AGB) and the post-AGB (PAGB) phase. The NIR is coherently linked to the visible and the ultraviolet (UV), so that the model is continuous on an exceptionally large wavelength range from 220Å up to 5μm. Moreover, a precise algorithm allows to follow very rapid evolutionary phases such as red supergiants or AGB crucial in the NIR. The nebular component is also computed in the NIR. The extinction correction is gas-dependent for spirals and ellipticals. A set of reference synthetic spectra at z=0, to which apply cosmological k- and evolution e- corrections for high-redshift galaxies, is built from fits of observational templates. Because of the lack of visible to NIR spectral templates for each Hubble type, we adopt statistical samples of colors, not fitted by previous models. A first application of this continuous model is to solve the problem of the slope of the bright galaxy counts from B=15 to 19 and of the normalization parameter φ_*_ of the Schechter luminosity function. Designed to be used currently and to take into account easily new observational and theoretical inputs, the model is built as a series of independent blocks. Any block is clearly identified and submitted to publication. Code sources, input and output data are available by anonymous ftp at ftp.iap.fr in /pub/from_users/pegase/ or at the WEB address of the authors: http://www.iap.fr/users/.