Ultraluminous infrared galaxies at high redshift: their position on the Madau plot and their fate

A major recent development in extragalactic astronomy has been the discover y of a population of galaxies that is luminous at submillimetre wavelengths . Estimates of their spectral energy distributions suggest that these galax ies are the high-redshift analogues of the ultraluminous infrared galaxies (ULIRGs) observed locally. Here we investigate the implications for the gal axy formation problem if this is indeed the case. We identify plausible (bu t non-unique) redshift-dependent galaxy luminosity functions that are consi stent with both source counts at 2800, 850, 450 and 175 mu m and far-infrar ed background radiation intensities at 850, 240 and 140 mu m In all our mod els, most of the submillimetre-luminous sources are distant galaxies with h igh bolometric luminosities greater than or equal to 10(12) L.. As for many local ULIRGs, it is not possible to determine whether these luminous galax ies are powered by starbursts, like the local galaxy Arp 220, or by active galactic nuclei (AGN), like the local galaxy Markarian 231. We investigate both possibilities. If the submillimetre-luminous galaxies are all starburs ts, then we predict that the fraction of the cosmic star formation rate in these objects is large, but does not necessarily dominate the star formatio n rate of the Universe - the Madau plot - at any redshift. Only a few per c ent by mass of the present-epoch spheroidal stellar population would have b een formed in such a population of star-forming galaxies, consistent with t he constraints on the number of galaxies with old stellar populations in th e field at low and intermediate redshifts derived from K-band surveys. If t he submillimetre-luminous galaxies are all powered by AGN, then the comovin g density of supermassive black holes on to which material is accreting at high redshift probably equals no more than a few per cent of the local dens ity of massive dark objects.