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T. Totani (Princeton University Observatory), T.T. Takeuchi (National Astronomical Observatory, Japan)
A new model of infrared galaxy counts and the cosmic background radiation (CBR) is developed by extending a model for optical/near-infrared galaxies. Important new characteristics of this model are that mass scale dependence of dust extinction is introduced based on the size-luminosity relation of optical galaxies, and that the big grain dust temperature T\rm dust is calculated based on a physical consideration for energy balance, rather than using the empirical relation between T\rm dust and total infrared luminosity L\rm IR found in local galaxies, which has been employed in most of previous works. Consequently, the local properties of infrared galaxies, i.e., optical/infrared luminosity ratios, L\rm IR-T\rm dust correlation, and infrared luminosity function are outputs predicted by the model, while these have been inputs in a number of previous models. Our model indeed reproduces these local properties reasonably well. Then we make predictions for faint infrared counts (in 15, 60, 90, 170, 450, and 850 \mum) and CBR by this model. We found considerably different results from most of previous works based on the empirical L\rm IR-T\rm dust relation; especially, it is shown that the dust temperature of starbursting primordial elliptical galaxies is expected to be very high (40--80K). This indicates that intense starbursts of forming elliptical galaxies should have occurred at z ~2--3, in contrast to the previous results that significant starbursts beyond z ~1 tend to overproduce the far-infrared (FIR) CBR detected by COBE/FIRAS. On the other hand, our model predicts that the mid-infrared (MIR) flux from warm/nonequilibrium dust is relatively weak in such galaxies making FIR CBR, and this effect reconciles the prima facie conflict between the upper limit on MIR CBR from TeV gamma-ray observations and the COBE\ detections of FIR CBR.
The authors thank the financial support by the Japan Society for Promotion of Science.