Herschel-ATLAS Galaxy Counts and High Redshift Luminosity Functions: The
  Formation of Massive Early Type Galaxies
  Exploiting the Herschel-ATLAS Science Demonstration Phase (SDP) survey data,
we have determined the luminosity functions (LFs) at rest-frame wavelengths of
100 and 250 micron and at several redshifts z>1, for bright sub-mm galaxies
with star formation rates (SFR) >100 M_sun/yr. 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*10^12 M_sun) amounts to ~7*10^8 yr. Given the
SFRs, which are in the range 10^2-10^3 M_sun/yr, this timescale implies final
stellar masses of order of 10^11-10^12 M_sun. The corresponding stellar mass
function matches the observed mass function of passively evolving galaxies at
z>1. The comparison of the statistics for sub-mm and UV selected galaxies
suggests that the dust-free, UV bright phase, is >10^2 times shorter than the
sub-mm 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 micron to ~1 mm. Owing to the steepness of the
counts and their relatively broad frequency range, this result suggests that
the dispersion of sub-mm SEDs of z>1 galaxies around the reference one is
rather small.
