Morphological and photometric evolution of ultraluminous infrared galaxies: The nature of faint scuba sources

We investigate when and how a dusty starburst galaxy merger can be heavily obscured by dust and consequently becomes an ultraluminous infrared galaxy (ULIRG), based on numerical simulations of chemodynamical and photometric e volution of dusty gas-rich major galaxy mergers. We found that a major gala xy merger is more likely to become a ULIRG preferentially in the merger lat e phase, when the two disks become very close and the very high density dus ty gas can obscure heavily the central secondary massive starburst. We furt hermore show how the optical and near-infrared morphology of a simulated UL IRG at intermediate (z = 0.4) and high redshift (z = 1-2) can be observed b y the Hubble Space Telescope (HST) in order to present a plausible explanat ion for the origin of some host galaxies of the faint SCUBA sources recentl y observed by Small et al. The results of our numerical simulations imply t hat some SCUBA sources with apparently faint and compact HST morphology can be higher redshift dust-enshrouded starburst mergers with their outer low surface brightness tidal features hardly detectable in the present optics o f the HST.