We study the predicted sub-mm emission from massive galaxies in a Lambda-CDM
universe, using hydrodynamic cosmological simulations. Assuming that most of
the emission from newly formed stars is absorbed and reradiated in the
rest-frame far-IR, we calculate the number of galaxies that would be detected
in sub-mm surveys conducted with SCUBA. The predicted number counts are
strongly dependent on the assumed dust temperature and emissivity law. With
plausible choices for SED parameters (e.g., T=35 K, beta=1.0), the simulation
predictions reproduce the observed number counts above ~ 1 mJy. The sources
have a broad redshift distribution with median z ~ 2, in reasonable agreement
with observational constraints. However, the predicted count distribution may
be too steep at the faint end, and the fraction of low redshift objects may be
larger than observed.
In this physical model of the sub-mm galaxy population, the objects detected
in existing surveys consist mainly of massive galaxies (several M_*) forming
stars fairly steadily over timescales ~ 10^8-10^9 years, at moderate rates ~100
Msun/yr. The typical descendants of these sub-mm sources are even more massive
galaxies, with old stellar populations, found primarily in dense environments.
While the resolution of our simulations is not sufficient to determine galaxy
morphologies, these properties support the proposed identification of sub-mm
sources with massive ellipticals in the process of formation. The most robust
and distinctive prediction of this model, stemming directly from the long
timescale and correspondingly moderate rate of star formation, is that the
far-IR SEDs of SCUBA sources have a relative high 850 micron luminosity for a
given bolometric luminosity. [Abridged]Comment: Submitted to ApJ. 34 pages including 8 PS figure
