The infrared properties of sources matched in the WISE all-sky and Herschel ATLAS surveys

Abstract

We describe the infrared properties of sources detected over similar to 36 deg(2) of sky in the GAMA 15 hr equatorial field, using data from both the Herschel Astrophysical Terahertz Large-Area Survey (H-ATLAS) and Wide-field Infrared Survey (WISE). With 5 sigma point-source depths of 34 and 0.048 mJy at 250 mu m and 3.4 mu m, respectively, we are able to identify 50.6% of the H-ATLAS sources in the WISE survey, corresponding to a surface density of similar to 630 deg(-2). Approximately two-thirds of these sources have measured spectroscopic or optical/near-IR photometric redshifts of z < 1. For sources with spectroscopic redshifts at z < 0.3, we find a linear correlation between the infrared luminosity at 3.4 mu m and that at 250 mu m, with +/- 50% scatter over similar to 1.5 orders of magnitude in luminosity, similar to 10(9)-10(10.5) L-circle dot. By contrast, the matched sources without previously measured redshifts (r greater than or similar to 20.5) have 250-350 mu m flux density ratios which suggest either high-redshift galaxies (z greater than or similar to 1.5) or optically faint low-redshift galaxies with unusually low temperatures (T less than or similar to 20). Their small 3.4-250 mu m flux ratios favor a high-redshift galaxy population, as only the most actively star-forming galaxies at low redshift (e.g., Lambda rp 220) exhibit comparable flux density ratios. Furthermore, we find a relatively large active galactic nucleus fraction (similar to 30%) in a 12 mu m flux-limited subsample of H-ATLAS sources, also consistent with there being a significant population of high-redshift sources in the no-redshift sample.