Models for Multiband IR Surveys

Empirical 'backward-evolution' models are developed for multiband IR surveys. A library consisting of realistic Spectral Energy Distributions (SEDs) of 837 local IR galaxies (IRAS 25$\mu m$ selected) covering from UV (1000{\AA}) to radio (20cm) is exploited to link coherently the surveys in different wavebands, under the assumption that the local correlation between SEDs and MIR luminosities can be applied to earlier epochs of the Universe. Assuming a $\Lambda$-Cosmology ($\Omega_\Lambda =0.7$, $\Omega_m = 0.3$), comparisons between results of model simulations and results of optical, NIR, MIR, FIR, submm surveys and the results on the Cosmic IR Background (CIB) available in the literature indicate that an evolution model assuming that before z=1.5 the population of starburst galaxies undergo a strong luminosity evolution ($L=L_0\times (1+z)^{4.2}$) and at the same time a strong density evolution ($\rho=\rho_0\times (1+z)^{2}$), the normal late-type galaxy population undergo a passive luminosity evolution ($L=L_0\times (1+z)^{1.5}$), and the galaxies with AGNs undergo a luminosity evolution similar to the evolution of optical QSOs ($L=L_0\times (1+z)^{3.5}$), and after z=1.5 all these evolutions drop down as $(1+z)^{-3}$, gives the best fit to the data. Predictions on number counts, confusion limits, redshift distributions, and color-color diagrams are made for multiband surveys using the upcoming SIRTF satellite. It is found that several SIRTF colors can be useful indicators of galaxy populations and redshifts.