Predictions for Cosmological Infrared Surveys from Space with the Multiband Imaging Photometer forSIRTF

We make predictions for the cosmological surveys to be conducted byMIPS/SIRTF at 24, 70 and 160 microns, for the GTO and the legacy programs,using the latest knowledge of the instrument. In addition to detector andcirrus confusion noise, we discuss in detail the derivation of the confusionnoise due to extragalactic sources, that depends strongly on the shape of thesource counts at a given wavelength and on the telescope and detector pixelsizes. We show that it is wise in general to compare the classical photometriccriterion and the so called source density criterion to predict the confusionlevels. We obtain, using the model of Lagache, Dole, & Puget (2002) limitingfluxes of 50 microJy, 3.2 mJy and 36 mJy at 24, 70 and 160 microns (resp.). Wecompute the redshift distributions of the detected sources at each wavelength,and show that they extend up to z ~ 2.7 at 24 microns and up to z ~ 2.5 at 70and 160 microns, leading to resolve at most 69, 54 and 24% of the CosmicInfrared Background (CIB) at 24, 70 and 160 microns (resp.). We estimate whichgalaxy populations will be used to derive the luminosity function evolutionwith redshift. We also give the redshift distributions of the unresolvedsources in the FIR range, that dominates the fluctuations of the CIB, and apredicted power spectrum showing the feasibility of fluctuations (due toPoissonian & clustered source distributions) measurements. The main conclusionis that MIPS (and SIRTF in general) cosmological surveys will greatly improveour understanding of galaxy evolution by giving data with unprecedentedaccuracy in the mid and far infrared range.