Abstract
ABSTRACTInfrared Imaging Surveyor (IRIS) is a satellite that will be launched in the beginning of 2003. One of the main purposes of the IRIS mission is an all‐sky survey at far‐infrared (FIR) wavelengths with a flux limit much deeper than that of IRAS. In order to examine the performance of the survey, we estimated the FIR galaxy counts in four (50, 70, 120, and 150 μm) bands based on some models. We adopted a multicomponent model that consists of cirrus and starburst components for galaxy spectra and the nearby FIR luminosity function derived from that of IRAS galaxies. We derived the number counts, redshift distributions, and infrared diffuse background radiation spectra for (1) no evolution, (2) pure luminosity evolution, and (3) pure density evolution with q0 = 0.1 and 0.5. We found that a large number of galaxies (∼a few ×106 in the whole sky) will be detected in this survey. With the aid of a vast number of detections, we will detect the effect of galaxy evolution and evaluate the amplitude of evolution at least in the nearby universe in the IRIS survey, though it will be still difficult to constrain which type of evolution takes place from the number count alone. We also studied the estimation of redshifts of detected galaxies by their infrared colors alone. Although significant contamination takes place among nearby faint galaxies and high‐z ones, we found that rough estimation of galaxy redshift can be practicable by jointly using present and future optical surveys.
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