The Herschel-ATLAS Data Release 1 Paper I: Maps, Catalogues and Number
  Counts
  We present the first major data release of the largest single key-project in
area carried out in open time with the Herschel Space Observatory. The Herschel
Astrophysical Terahertz Large Area Survey (H-ATLAS) is a survey of 600 deg^2 in
five photometric bands - 100, 160, 250, 350 and 500 um - with the PACS and
SPIRE cameras. In this paper and a companion paper (Bourne et al. 2016) we
present the survey of three fields on the celestial equator, covering a total
area of 161.6 deg^2 and previously observed in the Galaxy and Mass Assembly
(GAMA) spectroscopic survey. This paper describes the Herschel images and
catalogues of the sources detected on the SPIRE 250 um images. The 1-sigma
noise for source detection, including both confusion and instrumental noise, is
7.4, 9.4 and 10.2 mJy at 250, 350 and 500 um. Our catalogue includes 120230
sources in total, with 113995, 46209 and 11011 sources detected at >4-sigma at
250, 350 and 500 um. The catalogue contains detections at >3-sigma at 100 and
160 um for 4650 and 5685 sources, and the typical noise at these wavelengths is
44 and 49 mJy. We include estimates of the completeness of the survey and of
the effects of flux bias and also describe a novel method for determining the
true source counts. The H-ATLAS source counts are very similar to the source
counts from the deeper HerMES survey at 250 and 350 um, with a small difference
at 500 um. Appendix A provides a quick start in using the released datasets,
including instructions and cautions on how to use them.
