SPITZER -IRAC IDENTIFICATION OF HERSCHEL -ATLAS SPIRE SOURCES

We use Spitzer-IRAC data to identify near-infrared counterparts to submillimeter galaxies detected with Herschel-SPIKE at 250 [mu]m in the Herschel Astrophysical Terahertz Large Area Survey. Using a likelihood ratio analysis we identify 146 reliable IRAC counterparts to 123 SPIRE sources out of the 159 in the survey area. We find that, compared to the field population, the SPIRE counterparts occupy a distinct region of the 3.6 and 4.5 [mu]m color-magnitude space, and we use this property to identify 23 further 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 4-5 sources. Among the 73 counterparts that are undetected in Sloan Digital Sky Survey, 57 have both 3.6 and 4.5 [mu]m 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 super(10)-10 super(11) L sub([middot in circle]) total IR luminosities and are not intense starbursting galaxies as those found at z ~ 2, but they have a factor of 2-3 above average specific star formation rates compared to near-IR selected galaxy samples.