Contribution of starburst mergers at z ∼ 1 to the strong evolution of infrared and submillimeter deep surveys

Recent far-infrared and submillimetre waveband observations revealed huge amount of Ultraluminous Infrared Galaxies (ULIGs) with infrared luminosities > 10 L⊙. These sources are proposed to lie at redshift above one, and normally interacting systems with very dusty environments. We discussed in a previous paper that a population of fast evolving infrared burst phase triggered by gas rich mergers at z ∼ 1 interpreted successfully the steep slope at faint IRAS 60μm source counts within the flux range of 100mJy ∼ 1Jy, leaving still the infrared background level at this wavelength compatible with the upper limit from recent high energy TeV γ ray detection of Mrk501. To extend the model to mid and far infrared wavelength, we adopt a reasonable template spectral energy distribution as typical for nearby infrared bright starburst galaxies (Lir <= 10 12 L⊙), such as Arp220. We construct the SED for the dusty starburst mergers at z ∼ 1 by a simple dust extinction law and a thermal continuum assumption for the far-infrared emission. Since the radiation process at mid-infrared for these starburst merging systems is still uncertain, we assume it is similar to the MIR continuum of Arp220, but modify it by the observed flux correlation of ULIGs from IRAS, ISOCAM deep surveys. We show in this paper that the strong evolution of the European Large Area ISO Survey (ELAIS) at 90μm, ISO 170μm and the Submillimeter deep survey at 850μm could be sufficiently accounted for by such an evolutionary scenario, especially for the hump of the ISOCAM 15μm source count around 0.4mJy. From current best fit results, we find that the dust temperature of those extremely bright starburst merging system at z ∼ 1 would be higher than that of Arp220 for a reconciliation of the multi-wavelength infrared deep surveys. We thus propose that the infrared burst phase of dusty starburst galaxies or AGNs from gas rich mergers at z ∼ 1 could contribute significantly to the strong evolution of the IRAS 60μm, the ISO 15μm, 90μm, 170μm, as well as the SCUBA 850μm number counts, meanwhile compatible with the current observational limits of cosmic infrared background and the redshift distributions. The major difference of our current model prediction is that we see a fast convergence of the differential number counts at 60μm below 50mJy, which is about a factor of two brighter than other model predictions. Future infrared satellite like Astro-F, SIRTF would give strong constraints to the models.