Exploiting the Herschel Astrophysical Terahertz Large Area Survey
Science Demonstration Phase survey data, we have determined the
luminosity functions (LFs) at rest-frame wavelengths of 100 and 250
μm and at several redshifts z >~ 1, for bright submillimeter
galaxies with star formation rates (SFRs) >~ 100 M ⊙
yr-1. We find that the evolution of the comoving LF is strong
up to z ≈ 2.5, and slows down at higher redshifts. From the LFs and
the information on halo masses inferred from clustering analysis, we
derived an average relation between SFR and halo mass (and its scatter).
We also infer that the timescale of the main episode of dust-enshrouded
star formation in massive halos (M H >~ 3 ×
1012 M ⊙) amounts to ~7 × 108
yr. Given the SFRs, which are in the range of
102-103 M ⊙ yr-1, this
timescale implies final stellar masses of the order of
1011-1012 M ⊙. The corresponding
stellar mass function matches the observed mass function of passively
evolving galaxies at z >~ 1. The comparison of the statistics for
submillimeter and UV-selected galaxies suggests that the dust-free, UV
bright phase is >~ 102 times shorter than the
submillimeter bright phase, implying that the dust must form soon after
the onset of star formation. Using a single reference spectral energy
distribution (SED; the one of the z ≈ 2.3 galaxy SMM J2135-0102), our
simple physical model is able to reproduce not only the LFs at different
redshifts >1 but also the counts at wavelengths ranging from 250
μm to ≈1 mm. Owing to the steepness of the counts and their
relatively broad frequency range, this result suggests that the
dispersion of submillimeter SEDs of z > 1 galaxies around the
reference one is rather small.
Herschel is an ESA space observatory with science instruments provided
by European-led Principal Investigator consortia and with important
participation from NASA.