H-ATLAS: PACS imaging for the Science Demonstration Phase

Ibar, Edo; Ivison, R. J.; Cava, A.; Rodighiero, G.; Buttiglione, S.; Temi, P.; Frayer, D.; Fritz, J.; Leeuw, L.; Baes, M.; Rigby, E.; Verma, A.; Serjeant, S.; Müller, T.; Auld, R.; Dariush, A.; Dunne, L.; Eales, S.; Maddox, S.; Panuzzo, P.; Pascale, E.; Pohlen, M.; Smith, D.; Zotti, G. de; Vaccari, M.; Hopwood, R.; Cooray, A.; Burgarella, D. and Jarvis, M. (2010). H-ATLAS: PACS imaging for the Science Demonstration Phase. Monthly Notices of the Royal Astronomical Society, 409(1) pp. 38–47.

DOI: https://doi.org/10.1111/j.1365-2966.2010.17620.x

Abstract

We describe the reduction of data taken with the PACS instrument on board the Herschel Space Observatory in the Science Demonstration Phase of the Herschel-ATLAS (H-ATLAS) survey, specifically data obtained for a 4 × 4 deg² region using Herschel's fast-scan (60 arcsecs^-1) parallel mode. We describe in detail a pipeline for data reduction using customized procedures within HIPE from data retrieval to the production of science-quality images. We found that the standard procedure for removing cosmic ray glitches also removed parts of bright sources and so implemented an effective two-stage process to minimize these problems. The pronounced 1/f noise is removed from the timelines using 3.4- and 2.5-arcmin boxcar high-pass filters at 100 and 160 μm. Empirical measurements of the point spread function (PSF) are used to determine the encircled energy fraction as a function of aperture size. For the 100- and 160-μm bands, the effective PSFs are ~9 and ~13 arcsec (FWHM), and the 90-per cent encircled energy radii are 13 and 18 arcsec. Astrometric accuracy is good to ^<_~2 arcsec. The noise in the final maps is correlated between neighbouring pixels and rather higher than advertised prior to launch. For a pair of cross-scans, the 5σ point-source sensitivities are 125-165 mJy for 9-13 arcsec radius apertures at 100 μm and 150-240 mJy for 13-18 arcsec radius apertures at 160 μm.

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