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

Abstract

We present the largest submillimeter images that have been made of the extragalactic sky. The Herschel Astrophysical Terahertz Large Area Survey ( H -ATLAS) is a survey of 660 deg 2 with the PACS and SPIRE cameras in five photometric bands: 100, 160, 250, 350, and 500 μ m. In this paper we present the images from our two largest fields, which account for ∼75% of the survey. The first field is 180.1 deg 2 in size, centered on the north Galactic pole (NGP), and the second is 317.6 deg 2 in size, centered on the south Galactic pole. The NGP field serendipitously contains the Coma cluster. Over most (∼80%) of the images, the pixel noise, including both instrumental noise and confusion noise, is approximately 3.6, and 3.5 mJy pix −1 at 100 and 160 μ m, and 11.0, 11.1 and 12.3 mJy beam −1 at 250, 350 and 500 μ m, respectively, but reaches lower values in some parts of the images. If a matched filter is applied to optimize point-source detection, our total 1 σ map sensitivity is 5.7, 6.0, and 7.3 mJy at 250, 350, and 500 μ m, respectively. We describe the results of an investigation of the noise properties of the images. We make the most precise estimate of confusion in SPIRE maps to date, finding values of 3.12 ± 0.07, 4.13 ± 0.02, and 4.45 ± 0.04 mJy beam −1 at 250, 350, and 500 μ m in our un-convolved maps. For PACS we find an estimate of the confusion noise in our fast-parallel observations of 4.23 and 4.62 mJy beam −1 at 100 and 160 μ m. Finally, we give recipes for using these images to carry out photometry, both for unresolved and extended sources.