Faint End of 1.3 mm Number Counts Revealed by ALMA
  We present the faint end of number counts at 1.3 mm (238 GHz) obtained with
the Atacama Large Millimeter/submillimeter Array (ALMA). Band 6 observations
were carried out targeting 20 star-forming galaxies at z ~ 1.4 in the
Subaru/XMM-Newton Deep Survey field. In the observations, we serendipitously
detect 15 sources (>=3.8 sigma, S(1.3 mm) = 0.15-0.61 mJy) other than the
targeted sources. We create number counts by using these `sub-mJy sources',
which probe the faintest flux range among surveys at millimeter wavelengths.
The number counts are consistent with (flux-scaled) number counts at 850 um and
870 um obtained with gravitational lensing clusters. The ALMA number counts
agree well with model predictions, which suggest that these sub-mJy populations
are more like `normal' star-forming galaxies than `classical' SMGs with intense
star-forming activity. In this flux range, ~80% of the extragalactic background
light at 1.3 mm is resolved into individual sources.
