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

Abstract

Recent FIR/submm deep surveys revealed large number of ULIGs, which are proposed to lie at z>1, and in normally interacting systems with very dusty environments. We discussed in a previous paper that a population with a fast evolving infrared burst phase triggered by gas rich mergers at z~1 interpreted successfully the steep slope of IRAS 60um counts, leaving still a reasonable CIRB level at this wavelength. To extend the model to mid- and far-IR, we adopt a template SED as typical for nearby IR bright galaxies, such as Arp220. We construct the SED for the starburst mergers at z~1 by a simple dust extinction law and a thermal continuum assumption for the FIR emission. Since the radiation process at MIR for the merging systems is still uncertain, we assume it is similar to that 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 ELAIS 90um, ISO 170um and the SCUBA 850um could be sufficiently accounted for by such an evolutionary scenario, especially for the hump of the ISOCAM 15um source count around 0.4mJy. From current best fit results, we find that the dust temperature of those merging system at z~1 would be higher than that of Arp220 for a reconciliation of the multi-wavelength deep surveys. The major difference of our current model prediction is that we see a fast convergence of the differential number counts at 60um below 50mJy, which is about a factor of two brighter than other model predictions. Future IR satellite like Astro-F,SIRTF would give strong constraints to the models.