Sam Kim, Julie L. Wardlow, Asantha Cooray, S. Fleuren, W. Sutherland, A. A. Khostovan, R. Auld, M. Baes, R. S. Bussmann, S. Buttiglione, A. Cava, D. Clements, A. Dariush, G. De Zotti, L. Dunne, S. Dye, S. Eales, J. Fritz, R. Hopwood, E. Ibar, R. Ivison, M. Jarvis, S. Maddox, M. J. Michałowski, E. Pascale, M. Pohlen, E. Rigby, D. Scott, D. J. B. Smith, P. Temi, P. van der Werf
We use Spitzer-IRAC data to identify near-infrared counterparts to
submillimeter galaxies detected with Herschel-SPIRE at 250 um in the Herschel
Astrophysical Terahertz Large Area Survey (H-ATLAS). The IRAC catalogs cover ~
0.4 deg^2 of the H-ATLAS Science Demonstration Phase field, and are 50%
complete to 22.5 and 22.2 mag at 3.6 and 4.5 um, respectively. Using a
likelihood ratio analysis that accounts for the separation of SPIRE and IRAC
centroids, and the difference in the magnitude distribution of SPIRE
counterparts and background IRAC sources, we identify reliable counterparts to
123 SPIRE sources out of the 159 in the IRAC coverage area. We find that,
compared to the field population, the SPIRE counterparts occupy a distinct
region of 3.6 and 4.5 um 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 has 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. 73 of the
identified counterparts are detected in SDSS and have median redshift z = 0.3;
57 have z < 0.5 and the remaining 16 all have z < 0.8. Among the 73
counterparts that are undetected in SDSS, 57 have both 3.6 and 4.5 um 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.
View original:
http://arxiv.org/abs/1112.3653
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