The second Herschel-ATLAS Data Release - III: optical and near-infrared counterparts in the North Galactic Plane field

Abstract

This paper forms part of the second major public data release of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). In this work, we describe the identification of optical and near-infrared counterparts to the submillimetre detected sources in the $177$ deg${}^2$ North Galactic Plane (NGP) field. We used the likelihood ratio method to identify counterparts in the Sloan Digital Sky Survey and in the UKIRT Imaging Deep Sky Survey within a search radius of $10$ arcsec of the H-ATLAS sources with a $4\sigma$ detection at $250\mu$m. We obtained reliable ($R\ge 0.8$) optical counterparts with $r<22.4$ for 42429 H-ATLAS sources ($37.8$ per cent), with an estimated completeness of $71.7$ per cent and a false identification rate of $4.7$ per cent. We also identified counterparts in the near-infrared using deeper $K$-band data which covers a smaller $\sim 25$ deg${}^2$. We found reliable near-infrared counterparts to $61.8$ per cent of the $250$-$\mu$m-selected sources within that area. We assessed the performance of the likelihood ratio method to identify optical and near-infrared counterparts taking into account the depth and area of both input catalogues. Using catalogues with the same surface density of objects in the overlapping $\sim 25$ deg${}^2$ area, we obtained that the reliable fraction in the near-infrared ($54.8$ per cent) is significantly higher than in the optical ($36.4$ per cent). Finally, using deep radio data which covers a small region of the NGP field, we found that $80-90$ per cent of our reliable identifications are correct.

19 pages, 24 figures, submitted to MNRAS

References in corpus (11)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The SCUBA HAlf Degree Extragalactic Survey (SHADES) - III. Identification of radio and mid-infrared counterparts to submillimetre galaxies
• The UKIRT Infrared Deep Sky Survey Early Data Release
• The Herschel-ATLAS Data Release 1 Paper I: Maps, Catalogues and Number Counts
• The XMM-Newton wide-field survey in the COSMOS field: III. optical identification and multiwavelength properties of a large sample of X-ray selected sources
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• The Herschel-ATLAS Data Release 1 Paper II: Multi-wavelength counterparts to submillimetre sources
• The Herschel-ATLAS Data Release 2, Paper I. Submillimeter and Far-infrared Images of the South and North Galactic Poles: The Largest Herschel Survey of the Extragalactic Sky
• A complete distribution of redshifts for sub-millimetre galaxies in the SCUBA-2 Cosmology Legacy Survey UDS field
• Colour matters: the effects of lensing on the positional offsets between optical and submillimetre galaxies in Herschel-ATLAS

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