Herschel-ATLAS :
                    VISTA VIKING near-infrared counterparts in the Phase 1 GAMA 9-h data

Fleuren, S.; Sutherland, W.; Dunne, L.; Smith, Daniel; Maddox, S. J.; Gonzalez-Nuevo, J.; Findlay, J.; Auld, R.; Baes, M.; Bond, N. A.; Bonfield, D. G.; Bourne, N.; Cooray, A.; Buttiglione, S.; Cava, A.; Dariush, A.; De Zotti, G.; Driver, S. P.; Dye, S.; Eales, S.; Fritz, J.; Gunawardhana, M. L. P.; Hopwood, R.; Ibar, E.; Ivison, R. J.; Jarvis, M.J.; Kelvin, L.; Lapi, A.; Liske, J.; Michalowski, M. J.; Negrello, M.; Pascale, E.; Pohlen, M.; Prescott, M.; Rigby, E. E.; Robotham, A.; Scott, D.; Temi, P.; Thompson, Mark; Valiante, E.; van der Werf, P.

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Author

Fleuren, S.

Sutherland, W.

Dunne, L.

Smith, Daniel

Maddox, S. J.

Gonzalez-Nuevo, J.

Findlay, J.

Auld, R.

Baes, M.

Bond, N. A.

Bonfield, D. G.

Bourne, N.

Cooray, A.

Buttiglione, S.

Cava, A.

Dariush, A.

De Zotti, G.

Driver, S. P.

Dye, S.

Eales, S.

Fritz, J.

Gunawardhana, M. L. P.

Hopwood, R.

Ibar, E.

Ivison, R. J.

Jarvis, M.J.

Kelvin, L.

Lapi, A.

Liske, J.

Michalowski, M. J.

Negrello, M.

Pascale, E.

Pohlen, M.

Prescott, M.

Rigby, E. E.

Robotham, A.

Scott, D.

Temi, P.

Thompson, Mark

Valiante, E.

van der Werf, P.

Abstract

We identify near-infrared Ks-band counterparts to Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) submillimetre (submm) sources, using a preliminary object catalogue from the VISTA Kilo-degree Infrared Galaxy (VIKING) survey. The submm sources are selected from the H-ATLAS Phase 1 catalogue of the Galaxy and Mass Assembly 9-h field, which includes all objects detected at 250, 350 or with the instrument. We apply and discuss a likelihood ratio method for VIKING candidates within a search radius of 10 arcsec of the 22 000 SPIRE sources with a 5s detection at . We estimate the fraction of SPIRE sources with a counterpart above the magnitude limit of the VIKING survey to be Q0 similar to 0.73. We find that 11 294 (51 per cent) of the SPIRE sources have a best VIKING counterpart with a reliability R= 0.8, and the false identification rate of these is estimated to be 4.2 per cent. We expect to miss 5 per cent of true VIKING counterparts. There is evidence from Z-J and J-Ks colours that the reliable counterparts to SPIRE galaxies are marginally redder than the field population. We obtain photometric redshifts for 68 per cent of all (non-stellar) VIKING candidates with a median redshift of . We have spectroscopic redshifts for 3147 (28 per cent) of the reliable counterparts from existing redshift surveys. Comparing to the results of the optical identifications supplied with the Phase 1 catalogue, we find that the use of medium-deep near-infrared data improves the identification rate of reliable counterparts from 36 to 51 per cent.