Submillimetre and far-infrared images of the south and north galactic poles : the largest herschel survey of the extragalactic sky

We present the largest submillimeter images that have been made of the extragalactic sky. The HerschelAstrophysical Terahertz Large Area Survey (H -ATLAS) is a survey of 660 deg with the PACS and SPIRE cameras in five photometric bands: 100, 160, 250, 350, and 500μm. 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 in size centered on the North Galactic Pole (NGP) and the second field is 317.6 deg 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 3.5mJy pix at 100 and 160μm, and 11.0, 11.1 and 12.3mJy beam at 250, 350 and 500μm, respectively, but reaches lower values in some parts of the images. If a matched filter is applied to optimize point-source detection, our total 1σ map sensitivity is 5.7, 6.0, and 7.3mJy at 250, 350, and 500μm, 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± 0.04mJybeam at 250, 350, and 500μm in our un-convolved maps. For PACS we find an estimate of the confusion noise in our fast-parallel observations of 4.23 and 4.62mJy beam at 100 and 160μm. Finally, we give recipes for using these images to carry out photometry, both for unresolved and extended sources.