Spectral and photometric evolution of simple stellar populations at various metallicities

Abstract

A new set of evolutionary synthesis spectra are presented for Simple Stellar Populations (SSPs) covering ranges in metallicity from 0.02 ≤ Z/Z⊙ ≤ 2.5 and ages from 4 × 106 yr ≤ t ≤ 16 Gyr. They are based on the most recent isochromes from the Padova group that extend earlier models by the inclusion of the thermal pulsing AGB phase for stars in the mass range 2 M⊙ ≤ m ≤ 7 M⊙ in accordance with the fuel consumption theorem. We show that with respect to earlier models, inclusion of the TP-AGB phase leads to significant changes in the (V - I) and (V - K) colors of SSPs in the age range from 108 to ≳ 109 yr. Using model atmosphere spectra from Lejeune et al. (1997, 1998), we calculate the spectral evolution of single burst populations of various metallicities covering the wavelength range from 90 Å through 160 μm. Isochrone spectra are convolved with filter response functions to describe the time evolution of luminosities and colors in Johnson, Thuan & Gunn, Koo, HST, Washington and Strömgren filters. The models and their results are not only intended for use in the interpretation of star clusters but also for combination with any kind of dynamical galaxy formation and/or evolution model that contains a star formation criterion. Moreover, the evolution of these single burst single metallicity stellar populations is readily folded with any kind of star formation - and eventually chemical enrichment - history to describe the evolutionary spectral synthesis of composite stellar populations like galaxies of any type with continuous or discontinuous star formation. For these latter purposes we also present the time evolution of ejection rates for gas and metals for two different Initial Mass Functions (IMFs) as well as cosmological and evolutionary corrections for all the filters as a function of redshift for 0 ≤ z ≤ 5 and two different cosmologies. Extensive data files are provided in the electronic version, at CDS, and at our above www-address.