The source counts of submillimetre galaxies detected at 1.1 mm
  The source counts of galaxies discovered at sub-millimetre and millimetre
wavelengths provide important information on the evolution of infrared-bright
galaxies. We combine the data from six blank-field surveys carried out at 1.1
mm with AzTEC, totalling 1.6 square degrees in area with root-mean-square
depths ranging from 0.4 to 1.7 mJy, and derive the strongest constraints to
date on the 1.1 mm source counts at flux densities S(1100) = 1-12 mJy. Using
additional data from the AzTEC Cluster Environment Survey to extend the counts
to S(1100) ~ 20 mJy, we see tentative evidence for an enhancement relative to
the exponential drop in the counts at S(1100) ~ 13 mJy and a smooth connection
to the bright source counts at >20 mJy measured by the South Pole Telescope;
this excess may be due to strong lensing effects. We compare these counts to
predictions from several semi-analytical and phenomenological models and find
that for most the agreement is quite good at flux densities > 4 mJy; however,
we find significant discrepancies (>3sigma) between the models and the observed
1.1 mm counts at lower flux densities, and none of them are consistent with the
observed turnover in the Euclidean-normalised counts at S(1100) < 2 mJy. Our
new results therefore may require modifications to existing evolutionary models
for low luminosity galaxies. Alternatively, the discrepancy between the
measured counts at the faint end and predictions from phenomenological models
could arise from limited knowledge of the spectral energy distributions of
faint galaxies in the local Universe.
