Spitzer IRAC identification of Herschel-ATLAS SPIRE sources
  We use spitzer-IRAC data to identify near-infrared counterparts to
submillimeter galaxies detected with Herschel-SPIRE at 250um in the Herschel
Astrophysical Terahertz Large Area Survey (H-ATLAS). Using a likelihood ratio
analysis we identify 146 reliable IRAC counterparts to 123 SPIRE sources out of
the 159. We find that, compared to the field population, the SPIRE counterparts
occupy a distinct region of 3.6 and 4.5um color-magnitude space, and we use
this property to identify a further 23 counterparts to 13 SPIRE sources. The
IRAC identification rate of 86% is significantly higher than those that have
been demonstrated with wide-field ground-based optical and near-IR imaging of
Herschel fields. We estimate a false identification rate of 3.6%, corresponding
to 4 to 5 sources. Among the 73 counterparts that are undetected in SDSS, 57
have both 3.6 and 4.5um coverage. Of these 43 have [3.6] - [4.5]> 0 indicating
that they are likely to be at z > 1.4. Thus, ~ 40% of identified SPIRE galaxies
are likely to be high redshift (z > 1.4) sources. We discuss the statistical
properties of the IRAC-identified SPIRE galaxy sample including far-IR
luminosities, dust temperatures, star-formation rates, and stellar masses. The
majority of our detected galaxies have 10^10 to 10^11 L_sun total IR
luminosities and are not intense starbursting galaxies as those found at z ~ 2,
but they have a factor of 2 to 3 above average specific star-formation rates
compared to near-IR selected galaxy samples.
