A robust method for investigating galactic evolution in the submillimetre waveband -- II. The submillimetre background and source counts

This is the second of two papers describing a model of galactic evolution inthe submillimetre waveband. The model incorporates a self-consistent treatmentof the evolution of dust and stars, is normalized to the submillimetreproperties of galaxies in the local universe, and can be used to makepredictions for both disk and elliptical galaxies and for `closed-box',`inflow', and `outflow' models of galactic evolution. In Paper I weinvestigated whether it is possible to explain the extreme dust masses ofhigh-redshift quasars and radio galaxies by galactic evolution. In this paperwe use the model to make predictions of the submillimetre background and sourcecounts. All our disk-galaxy models exceed at short wavelengths thesubmillimetre background recently measured by Puget et al. (1996). We also findthat it is possible to fit the background over the entire wavelength range witha elliptical model but not with a disk model. We make source count predictionsat 190 $\mu$m for the ISOPHOT instrument on ISO and at 850 $\mu$m for SCUBA. Weshow that the shape of the 850 $\mu$ m source counts depends almost entirely onthe mass spectrum of the radiating objects. Finally, we consider thelimitations of the models. We find that one of the biggest uncertainties in themodel is our lack of information about the submillimetre properties of nearbygalaxies, in particular the lack of a direct measurement of the submillimetreluminosity function.Comment: 17 pages, 9 postscript figures, TEX, accepted by MNRA