Models for multiband infrared surveys

Empirical "backward" galaxy evolution models for IR bright galaxies are con strained using multiband IR surveys. A new Monte Carlo algorithm is develop ed for this task. It exploits a large library of realistic spectral energy distributions (SEDs) of 837 local IR galaxies (IRAS 25 mum selected) from t he UV (1000 Angstrom) to the radio (20 cm), including Infrared Space Observ atory (ISO) measured 3-13 mum unidentified broad features (UIBs). The basic assumption is that the local correlation between SEDs and mid-infrared (MI R) luminosities can be applied to earlier epochs of the universe, an assump tion that will be strongly tested by SIRT F. By attaching an SED appropriat ely drawn from the SED library to every source predicted by a given model, the algorithm enables simultaneous comparisons with multiple surveys in a w ide range of wave bands. Three populations of IR sources are considered in the evolution models. These include (1) starburst galaxies, (2) normal late -type galaxies, and (3) galaxies with active galactic nuclei (AGNs). Constr ained by data from the literature, our best-Dt model ("peak model II) predi cts that since z = 1.5 the population of starburst galaxies undergoes a ver y strong luminosity evolution [L = L-0(1 + z)(4.2)] and also strong density evolution [rho = rho (0)(1 + z)(2)], the normal late-type galaxy populatio n undergoes a passive luminosity evolution [L = L-0(1 + z)(1.5)], and the g alaxies with an AGN undergo a pure luminosity evolution similar to that of optical QSOs [L = L-0(1 + z)(3.5)]. Prior at z greater than or equal to 1.5 all evolution rates drop as (1 + z)(-3). The luminosity evolution results in evolution of SEDs of IR bright sources because of the luminosity depende nce of the SEDs. Predictions for number counts, confusion limits, redshift distributions, and color-color diagrams are made for multiband surveys usin g the upcoming SIRT F satellite. A Lambda cosmology (Omega (Lambda) = 0.7, Omega (m) = 0.3, H-0 = 75 km s(-1) Mpc(-1)) is assumed throughout the paper .