Hi-GAL, the Herschel infrared Galactic Plane Survey: photometric maps and compact source catalogues

First data release for the inner Milky Way: +68° ≥ l ≥ −70°^⋆,⋆⋆

¹ INAF–Istituto di Astrofisica e Planetologia Spaziale, via Fosso del Cavaliere 100, 00133 Roma, Italy
e-mail: molinari@iaps.inaf.it
² Jodrell Bank centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK
³ STFC, Rutherford Appleton Labs, Didcot, OX11QX, UK
⁴ Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, 21218 MD, USA
⁵ Centre for Astrophysics and Space Astronomy (CASA), Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, USA
⁶ Astrophysics Research Institute, Liverpool John Moores University, Ic2 Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK
⁷ Department of Physics & Astronomy, University of Calgary, Calgary, ABT2N 1N4, Canada
⁸ LAM, Université de Provence, 13013 Marseille, France
⁹ ESA, Directorate of Science, Scientific Support Office, European Space Research and Technology Centre (ESTEC/SCI-S), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹⁰ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA, Leiden, The Netherlands
¹¹ DIET, Università di Roma “La Sapienza”, 00185 Roma, Italy
¹² Infrared Processing Analysis centre, California Institute of Technology, Pasadena, CA 91125, USA
¹³ Herschel Science centre, ESA/ESAC, PO Box 78, Villanueva de la Cañada, 28691 Madrid, Spain
¹⁴ ASI Science Data centre, 00044 Frascati, Roma, Italy
¹⁵ Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Ferrara e Sezione INFN di Ferrara, via Saragat 1, 44100 Ferrara, Italy
¹⁶ Dipartimento di Fisica, Università di Roma “La Sapienza”, P. le Aldo Moro 2, 00138 Roma, Italy
¹⁷ Departamento de Fisica, Universidad de Atacama, Copiapó, Chile
¹⁸ INAF–Istituto di Radioastronomia, via P. Gobetti 101, 40129 Bologna, Italy
¹⁹ Department of Physics and Astronomy, University College London, London, WC1E 6BT, UK
²⁰ Université de Toulouse, UPS, CESR, and CNRS, UMR5187, Toulouse, France
²¹ CNRS, IRAP, 9 Av. Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
²² Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON M5S, Canada
²³ European Southern Observatory, Garching bei München, Germany
²⁴ INAF–Osservatorio Astrofisico di Arcetri, Firenze, Italy
²⁵ Space Science Institute, Boulder, CO, USA
²⁶ Laboratoire AIM, CEA/DSM – INSU/CNRS – Université Paris Diderot, IRFU/SAp CEA-Saclay, 91191 Gif-sur-Yvette, France
²⁷ Institut de RadioAstronomie Millimétrique (IRAM), Granada, Spain
²⁸ Spitzer Science centre, California Institute of Technology, Pasadena, CA 9/125, USA
²⁹ HYGEOS, Euratechnologies, 165 Avenue de Bretagne, 59000 Lille, France
³⁰ Université de Strasbourg, CNRS, UMR 7550, 11 rue de l’Université, 67000 Strasbourg, France
³¹ Department ofAstrophysics, Nagoya University, 464-8601 Nagoya, Japan
³² School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
³³ National Astronomical Observatories, Chinese Academy of Sciences, 100864 Beijing, PR China
³⁴ Departement de Physique, Université Laval, Québec, QC G1V OA6, Canada
³⁵ The SETI Institute, 189 Bernardo Avenue Suite 100, Mountain View, CA 94043, USA
³⁶ School of Physics and Astronomy, Cardiff University, Cardiff, UK
³⁷ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
³⁸ Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
³⁹ Univ. Bordeaux, LAB, UMR 5804, CNRS, 33270, Floirac, France
⁴⁰ SRON Netherlands Institute for Space Research, Zernike Building, PO Box 800, 9700 AV Groningen, The Netherlands
⁴¹ Dipartimento di Matematica e Fisica, Università del Salento, Lecce, Italy
⁴² Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB, UK
⁴³ INAF–Osservatorio Astrofisico di Catania, Catania, Italy
⁴⁴ Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
⁴⁵ Max-Planck-Institut für Radioastronomie (MPIfR), 53121 Bonn, Germany

Received: 22 April 2015
Accepted: 10 February 2016

Abstract

Aims. We present the first public release of high-quality data products (DR1) from Hi-GAL, the Herschel infrared Galactic Plane Survey. Hi-GAL is the keystone of a suite of continuum Galactic plane surveys from the near-IR to the radio and covers five wavebands at 70, 160, 250, 350 and 500 μm, encompassing the peak of the spectral energy distribution of cold dust for 8 ≲ T ≲ 50 K. This first Hi-GAL data release covers the inner Milky Way in the longitude range 68° ≳ ℓ ≳ −70° in a | b | ≤ 1° latitude strip.

Methods. Photometric maps have been produced with the ROMAGAL pipeline, which optimally capitalizes on the excellent sensitivity and stability of the bolometer arrays of the Herschel PACS and SPIRE photometric cameras. It delivers images of exquisite quality and dynamical range, absolutely calibrated with Planck and IRAS, and recovers extended emission at all wavelengths and all spatial scales, from the point-spread function to the size of an entire 2°× 2° “tile” that is the unit observing block of the survey. The compact source catalogues were generated with the CuTEx algorithm, which was specifically developed to optimise source detection and extraction in the extreme conditions of intense and spatially varying background that are found in the Galactic plane in the thermal infrared.

Results. Hi-GAL DR1 images are cirrus noise limited and reach the 1σ-rms predicted by the Herschel Time Estimators for parallel-mode observations at 60′′ s^-1 scanning speed in relatively low cirrus emission regions. Hi-GAL DR1 images will be accessible through a dedicated web-based image cutout service. The DR1 Compact Source Catalogues are delivered as single-band photometric lists containing, in addition to source position, peak, and integrated flux and source sizes, a variety of parameters useful to assess the quality and reliability of the extracted sources. Caveats and hints to help in this assessment are provided. Flux completeness limits in all bands are determined from extensive synthetic source experiments and greatly depend on the specific line of sight along the Galactic plane because the background strongly varies as a function of Galactic longitude. Hi-GAL DR1 catalogues contain 123210, 308509, 280685, 160972, and 85460 compact sources in the five bands.