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

Purple Mountain Observatory, Academia Sinica, China; National Astronomical Observatories of China National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan

Corresponding author: ypwang@pmo.ac.cn

Received: 20 July 2001
Accepted: 29 November 2001

Abstract

Recent far-infrared and submillimetre waveband observations revealed a large number of Ultraluminous Infrared Galaxies (ULIGs) with infrared luminosities > . These sources are proposed to lie at redshifts above one, 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 predicted successfully the steep slope of faint IRAS 60 μm source counts within the flux range of 100 mJy ~ 1 Jy, still leaving the infrared background level at this wavelength compatible with the upper limit from recent high energy TeV γ ray detection of Mrk 501. To extend the model to mid and far infrared wavelengths, we adopt a reasonable template spectral energy distribution typical for nearby-infrared-bright starburst galaxies (), such as Arp 220. We construct the SED for the dusty starburst mergers at 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 Arp 220, but modify it by the observed flux correlation of ULIGs from IRAS and ISOCAM deep surveys. We show in this paper that the strong evolution of the European Large Area ISO Survey (ELAIS) at 90 μm, ISO 170 μm and the Submillimeter deep survey at 850 μm could be sufficiently accounted for by such an evolutionary scenario, especially the hump of the ISOCAM 15 μm source count around 0.4 mJy. From current best fit results, we find that the dust temperature of those extremely bright starburst merging system at would be higher than that of Arp 220 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 could contribute significantly to the strong evolution of the IRAS 60 μm, the ISO 15 μm, 90 μm, 170 μm, as well as the SCUBA 850 μm number counts, while being compatible with the current observational limits of the 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 60 μm below 50 mJy, which is about a factor of two brighter than other model predictions. Future infrared satellites like Astro-F or SIRTF would give strong constraints to the models.