Herschel-ATLAS Data Release III: Near-infrared counterparts in the South Galactic Pole field -- Another 100,000 submillimetre galaxies

TL;DR

This paper presents the third data release of the Herschel-ATLAS survey, identifying near-infrared counterparts to submillimetre sources, estimating false matches, and highlighting candidate gravitational lensing systems in the South Galactic Pole field.

Contribution

It provides a comprehensive catalog of near-infrared counterparts, assesses lensing probabilities, and introduces new methods for identifying multiple true counterparts in Herschel submillimetre sources.

Findings

57% of sources have high-probability near-infrared counterparts.

Estimated false identification rate is 4.8%.

Identified 41 candidate lensed systems and 5,923 likely lensed sources below 100 mJy.

Abstract

In this paper we present the third data release (DR3) of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). We identify likely near-infrared counterparts to submillimetre sources in the South Galactic Pole (SGP) field using the VISTA VIKING survey. We search for the most probable counterparts within 15 arcsec of each Herschel source using a probability measure based on the ratio between the likelihood the true counterpart is found close to the submillimetre source and the likelihood that an unrelated object is found in the same location. For 110 374 (57.0$\%$) sources we find galaxies on the near-infrared images where the probability that the galaxy is associated to the source is greater than 0.8. We estimate the false identification rate to be 4.8$\%$, with a probability that the source has an associated counterpart on the VIKING images of 0.835$\pm$0.009. We investigate the effects of gravitational lensing and present 41 (0.14 deg$^{-2}$) candidate lensed systems with observed flux densities > 100 mJy at 500 $\mu$m. We include in the data release a probability that each source is gravitationally lensed and discover an additional 5 923 sources below 100 mJy that have a probability greater than 0.94 of being gravitationally lensed. We estimate that $\sim$ 400 - 1 000 sources have multiple true identifications in VIKING based on the similarity of redshift estimates for multiple counterparts close to a Herschel source. The data described in this paper can be found at the H-ATLAS website.