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arXiv · 1606.09254

The Herschel-ATLAS Data Release 1 Paper II: Multi-wavelength counterparts to submillimetre sources

N. Bourne·L. Dunne·S. J. Maddox·S. Dye·C. Furlanetto·C. Hoyos·D. J. B. Smith·S. Eales·M. W. L. Smith·E. Valiante·M. Alpaslan·E. Andrae·I. K. Baldry·M. E. Cluver·A. Cooray·S. P. Driver·J. S. Dunlop·M. W. Grootes·R. J. Ivison·T. H. Jarrett·J. Liske·B. F. Madore·C. C. Popescu·A. G. Robotham·K. Rowlands·M. Seibert·M. A. Thompson·R. J. Tuffs·S. Viaene·A. H. Wright
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Abstract

This paper is the second in a pair of articles presenting data release 1 (DR1) of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS), the largest single open-time key project carried out with the Herschel Space Observatory. The H-ATLAS is a wide-area imaging survey carried out in five photometric bands at 100, 160, 250, 350 and 500$μ$m covering a total area of 600deg$^2$. In this paper we describe the identification of optical counterparts to submillimetre sources in DR1, comprising an area of 161 deg$^2$ over three equatorial fields of roughly 12$^\circ$x4.5$^\circ$ centred at 9$^h$, 12$^h$ and 14.5$^h$ respectively. Of all the H-ATLAS fields, the equatorial regions benefit from the greatest overlap with current multi-wavelength surveys spanning ultraviolet (UV) to mid-infrared regimes, as well as extensive spectroscopic coverage. We use a likelihood-ratio technique to identify SDSS counterparts at r<22.4 for 250-$μ$m-selected sources detected at $\geq$ 4$σ$ ($\approx$28mJy). We find `reliable' counterparts (reliability R$\geq$0.8) for 44,835 sources (39 per cent), with an estimated completeness of 73.0 per cent and contamination rate of 4.7 per cent. Using redshifts and multi-wavelength photometry from GAMA and other public catalogues, we show that H-ATLAS-selected galaxies at $z<0.5$ span a wide range of optical colours, total infrared (IR) luminosities, and IR/UV ratios, with no strong disposition towards mid-IR-classified AGN in comparison with optical selection. The data described herein, together with all maps and catalogues described in the companion paper (Valiante et al. 2016), are available from the H-ATLAS website at www.h-atlas.org.

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N. Bourne, L. Dunne, S. J. Maddox, S. Dye, C. Furlanetto, C. Hoyos, D. J. B. Smith, S. Eales, M. W. L. Smith, E. Valiante, M. Alpaslan, E. Andrae, I. K. Baldry, M. E. Cluver, A. Cooray, S. P. Driver, J. S. Dunlop, M. W. Grootes, R. J. Ivison, T. H. Jarrett, J. Liske, B. F. Madore, C. C. Popescu, A. G. Robotham, K. Rowlands, M. Seibert, M. A. Thompson, R. J. Tuffs, S. Viaene, A. H. Wright. 2016-07-15. The Herschel-ATLAS Data Release 1 Paper II: Multi-wavelength counterparts to submillimetre sources. https://doi.org/10.1093/mnras%2Fstw1654

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