PEGASE; 2, a metallicity-consistent spectral evolution model of galaxies: the documentation and the code

We provide here the documentation of the new version of the spectral evolution model PEGASE. PEGASE computes synthetic spectra of galaxies in the UV to near-IR range from 0 to 20 Gyr, for a given stellar IMF and evolutionary scenario (star formation law, infall, galactic winds). The radiation emitted by stars from the main sequence to the pre-supernova or white dwarf stage is calculated, as well as the extinction by dust. A simple modeling of the nebular emission (continuum and lines) is also proposed. PEGASE may be used to model starbursts as well as old galaxies. The main improvements of PEGASE.2 relative to PEGASE.1 (Fioc & Rocca-Volmerange 1997) are the following: (1)The stellar evolutionary tracks of the Padova group for metallicities between 0.0001 and 0.1 have been included; (2)The evolution of the metallicity of the interstellar medium (ISM) due to SNII, SNIa and AGB stars is followed. Stars are formed with the same metallicity as the ISM (instead of a solar metallicity in PEGASE.1), providing thus a metallicity-consistent model; (3)Lejeune et al.'s library of stellar spectra is used; (4)The extinction by dust is computed for geometries corresponding to disk and spheroidal galaxies using a radiative transfer code taking into account the scattering. The main outputs (as a function of time) are spectra, colors and magnitudes in various photometric systems, luminosities, type II and Ia supernovae rates, line intensities and equivalent widths, amount and metallicity of stars and gas, mass locked in stellar remnants, optical depth and total dust emission. The corresponding article (Fioc & Rocca-Volmerange 2000) will be submitted soon. A detailed modeling of the spectrum of the dust emission and of HII regions (Moy, Rocca-Volmerange & Fioc 2000) will be included in future versions