The data reduction pipeline for the Hi-GAL survey

ABSTRACT We present the data reduction pipeline for the Hi-GAL survey. Hi-GAL is a key project of theHerschel satellite which is mapping the inner part of the Galactic plane (|l| 670 ◦ and |b| 61 ◦ ),using 2 PACS and 3 SPIRE frequency bands, from 70µm to 500µm. Our pipeline relies onlypartially on the Herschel Interactive Standard Environment(HIPE) and features several newlydevelopedroutinesto performdatareduction,includingaccuratedataculling,noiseestimationand minimum variance map-making, the latter performed withthe ROMAGAL algorithm, adeep modification of the ROMA code already tested on cosmolog ical surveys. We discuss indepth the properties of the Hi-GAL Science Demonstration Phase (SDP) data.Key words: instrumentation – data reduction 1 INTRODUCTIONThe Herschel Space Observatory was launched from Kourou inMay 2009 aboard an Ariane 5 rocket. Two of three scientific in-struments on the focal plane (PACS and SPIRE) are capable to ob-serve the infrared sky with unprecedented angular resolution andsensitivity, providing photometric observations in 6 different bands(70µm, 100µm, 160µm, 250µm, 350µm and 500µm: Pilbratt et al.2010, and reference therein).The PACS photometer is composed of two bolometer arrays: a64×32 pixel matrix arranged from 8 monolithic subarrays of 16×16pixels each centered on the 70µm and 100µm wavelength (blue andgreen bands), and a 32 × 16 pixel matrix organized in two subar-rays for the band centered on 160µm (red band), see Poglitsch et al.(2010).SPIRE comprises a three band photometer, operating in spec-tral bands centered on 250µm, 350µm and 500µm. Every band usesa matrix of germanium bolometers (139, 88 and 43 respectively)coupled to hexagonally packed conical feed horns (Griffin et al.2010).In order to handle science data provided by the Herschel in-struments, including the data retrieval from the Herschel Science