Session 70 - Cosmic Backgrounds and the Distant Universe.
Oral session, Thursday, June 11
Presidio,

## [70.01] A model for source counts and redshift distributions of deep MIR surveys

C. Xu, P. B. Hacking, F. Fang, D. L. Shupe, C. J. Lonsdale, N. Lu, G. Helou (IPAC, JPL, Caltech), G. Stacey, M. Ashby (Cornell University)

In this work we incorporate the newest ISO results on the mid-infrared spectral-energy-distributions (MIR SED's) of galaxies into models for the number counts and redshift distributions of deep MIR surveys. A three-component model, with empirically determined MIR SED templates of a cirrus/PDR component (2) a starburst component and (3) an AGN component, is developed for infrared (3 --- 120\mu m) SED's of galaxies. The model includes a complete IRAS 25\mu m selected sample of 1406 local galaxies (z \leq 0.1). Results based on these 1406 spectra show that the MIR emission features cause significant effects on the z dependence of the K-corrections of MIR fluxes. This in turn will affect deep counts and redshift distributions of MIR surveys. It is pointed out that the dips-and-bumps on curves of MIR number counts, caused by the emission features, will be very useful indicators of redshift and of evolution mode. The strong emission features at \sim 6---8\mu m will help the detections of relatively high redshift (z\sim 2) galaxies in MIR surveys. On the other hand determinations of the evolutionary rate based on the slope of source counts, and studies on the large scale structures using the redshift distribution of MIR sources will have to treat the effects of the MIR emission features carefully.