Planck early results. XXI. Properties of the interstellar medium in the Galactic plane^⋆

¹ Aalto University Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland
² Agenzia Spaziale Italiana Science Data Center, c/o ESRIN, via Galileo Galilei, Frascati, Italy
³ Astroparticule et Cosmologie, CNRS (UMR7164), Université Denis Diderot Paris 7, Bâtiment Condorcet, 10 rue A. Domon et Léonie Duquet, Paris, France
⁴ Astrophysics Group, Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK
⁵ Atacama Large Millimeter/submillimeter Array, ALMA Santiago Central Offices, Alonso de Cordova 3107, Vitacura, Casilla 763 0355, Santiago, Chile
⁶ CITA, University of Toronto, 60 St. George St., Toronto, ON M5S 3H8, Canada
⁷ CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
⁸ California Institute of Technology, Pasadena, California, USA
⁹ Centre of Mathematics for Applications, University of Oslo, Blindern, Oslo, Norway
¹⁰ DAMTP, University of Cambridge, Centre for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA, UK
¹¹ DSM/Irfu/SPP, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
¹² DTU Space, National Space Institute, Juliane Mariesvej 30, Copenhagen, Denmark
¹³ Departamento de Física, Universidad de Oviedo, Avda. Calvo Sotelo s/n, Oviedo, Spain
¹⁴ Department of Astronomy and Astrophysics, University of Toronto, 50 Saint George Street, Toronto, Ontario, Canada
¹⁵ Department of Physics & Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia, Canada
¹⁶ Department of Physics, Gustaf Hällströmin katu 2a, University of Helsinki, Helsinki, Finland
¹⁷ Department of Physics, Princeton University, Princeton, New Jersey, USA
¹⁸ Department of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, Indiana, USA
¹⁹ Department of Physics, University of California, Berkeley, California, USA
²⁰ Department of Physics, University of California, One Shields Avenue, Davis, California, USA
²¹ Department of Physics, University of California, Santa Barbara, California, USA
²² Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois, USA
²³ Dipartimento di Fisica G. Galilei, Università degli Studi di Padova, via Marzolo 8, 35131 Padova, Italy
²⁴ Dipartimento di Fisica, Università La Sapienza, P. le A. Moro 2, Roma, Italy
²⁵ Dipartimento di Fisica, Università degli Studi di Milano, via Celoria 16, Milano, Italy
²⁶ Dipartimento di Fisica, Università degli Studi di Trieste, via A. Valerio 2, Trieste, Italy
²⁷ Dipartimento di Fisica, Università di Ferrara, via Saragat 1, 44122 Ferrara, Italy
²⁸ Dipartimento di Fisica, Università di Roma Tor Vergata, viadella Ricerca Scientifica 1, Roma, Italy
²⁹ Discovery Center, Niels Bohr Institute, Blegdamsvej 17, Copenhagen, Denmark
³⁰ Dpto. Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
³¹ European Southern Observatory, ESO Vitacura, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago, Chile
³² European Space Agency, ESAC, Planck Science Office, Camino bajo del Castillo, s/n, Urbanización Villafranca del Castillo, Villanueva de la Cañada, Madrid, Spain
³³ European Space Agency, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
³⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³⁵ Helsinki Institute of Physics, Gustaf Hällströmin katu 2, University of Helsinki, Helsinki, Finland
³⁶ INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, Catania, Italy
³⁷ INAF - Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, Padova, Italy
³⁸ INAF - Osservatorio Astronomico di Roma, via di Frascati 33, Monte Porzio Catone, Italy
³⁹ INAF - Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, Trieste, Italy
⁴⁰ INAF/IASF Bologna, via Gobetti 101, Bologna, Italy
⁴¹ INAF/IASF Milano, via E. Bassini 15, Milano, Italy
⁴² INRIA, Laboratoire de Recherche en Informatique, Université Paris-Sud 11, Bâtiment 490, 91405 Orsay Cedex, France
⁴³ IPAG: Institut de Planétologie et d’Astrophysique de Grenoble, Université Joseph Fourier, Grenoble 1/CNRS-INSU, UMR 5274, 38041 Grenoble, France
⁴⁴ Imperial College London, Astrophysics group, Blackett Laboratory, Prince Consort Road, London, SW7 2AZ, UK
⁴⁵ Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA
⁴⁶ Institut Néel, CNRS, Université Joseph Fourier Grenoble I, 25 rue des Martyrs, Grenoble, France
⁴⁷ Institut d’Astrophysique Spatiale, CNRS (UMR8617) Université Paris-Sud 11, Bâtiment 121, Orsay, France
⁴⁸ Institut d’Astrophysique de Paris, CNRS UMR7095, Université Pierre & Marie Curie, 98 bis boulevard Arago, Paris, France
⁴⁹ Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan
⁵⁰ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁵¹ Institute of Theoretical Astrophysics, University of Oslo, Blindern, Oslo, Norway
⁵² Instituto de Astrofísica de Canarias, C/vía Láctea s/n, La Laguna, Tenerife, Spain
⁵³ Instituto de Física de Cantabria (CSIC-Universidad de Cantabria), Avda. de los Castros s/n, Santander, Spain
⁵⁴ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California, USA
⁵⁵ Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK
⁵⁶ Kavli Institute for Cosmology Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
⁵⁷ LERMA, CNRS, Observatoire de Paris, 61 Avenue de l’Observatoire, Paris, France
⁵⁸ Laboratoire AIM, IRFU/Service d’Astrophysique - CEA/DSM - CNRS - Université Paris Diderot, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
⁵⁹ Laboratoire Traitement et Communication de l’Information, CNRS (UMR 5141) and Télécom ParisTech, 46 rue Barrault, 75634 Paris Cedex 13, France
⁶⁰ Laboratoire de Physique Subatomique et de Cosmologie, CNRS/IN2P3, Université Joseph Fourier Grenoble I, Institut National Polytechnique de Grenoble, 53 rue des Martyrs, 38026 Grenoble Cedex, France
⁶¹ Laboratoire de l’Accélérateur Linéaire, Université Paris-Sud 11, CNRS/IN2P3, Orsay, France
⁶² Lawrence Berkeley National Laboratory, Berkeley, California, USA
⁶³ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
⁶⁴ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁶⁵ MilliLab, VTT Technical Research Centre of Finland, Tietotie 3, Espoo, Finland
⁶⁶ National University of Ireland, Department of Experimental Physics, Maynooth, Co. Kildare, Ireland
⁶⁷ Niels Bohr Institute, Blegdamsvej 17, Copenhagen, Denmark
⁶⁸ Observational Cosmology, Mail Stop 367-17, California Institute of Technology, Pasadena, CA 91125, USA
⁶⁹ Optical Science Laboratory, University College London, Gower Street, London, UK
⁷⁰ SISSA, Astrophysics Sector, via Bonomea 265, 34136 Trieste, Italy
⁷¹ SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁷² School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff, CF24 3AA, UK
⁷³ Space Sciences Laboratory, University of California, Berkeley, California, USA
⁷⁴ Spitzer Science Center, 1200 E. California Blvd., Pasadena, California, USA
⁷⁵ Stanford University, Dept of Physics, Varian Physics Bldg, , 382 Via Pueblo Mall, Stanford, California, USA
⁷⁶ Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse Cedex 4, France
⁷⁷ Universities Space Research Association, Stratospheric Observatory for Infrared Astronomy, MS 211-3, Moffett Field, CA 94035, USA
⁷⁸ University of Granada, Departamento de Física Teórica y del Cosmos, Facultad de Ciencias, Granada, Spain
⁷⁹ University of Miami, Knight Physics Building, 1320 Campo Sano Dr., Coral Gables, Florida, USA
⁸⁰ Warsaw University Observatory, Aleje Ujazdowskie 4, 00-478 Warszawa, Poland

Received: 7 January 2011
Accepted: 9 June 2011

Abstract

Planck has observed the entire sky from 30 GHz to 857GHz. The observed foreground emission contains contributions from different phases of the interstellar medium (ISM). We have separated the observed Galactic emission into the different gaseous components (atomic, molecular and ionised) in each of a number of Galactocentric rings. This technique provides the necessary information to study dust properties (emissivity, temperature, etc.), as well as other emission mechanisms as a function of Galactic radius. Templates are created for various Galactocentric radii using velocity information from atomic (neutral hydrogen) and molecular (¹²CO) observations. The ionised template is assumed to be traced by free-free emission as observed by WMAP, while 408 MHz emission is used to trace the synchrotron component. Gas emission not traced by the above templates, namely “dark gas”, as evidenced using Planck data, is included as an additional template, the first time such a component has been used in this way. These templates are then correlated with each of the Planck frequency bands, as well as with higher frequency data from IRAS and DIRBE along with radio data at 1.4 GHz. The emission per column density of the gas templates allows us to create distinct spectral energy distributions (SEDs) per Galactocentric ring and in each of the gaseous tracers from 1.4 GHz to 25 THz (12μm). The resulting SEDs allow us to explore the contribution of various emission mechanisms to the Planck signal. Apart from the thermal dust and free-free emission, we have probed the Galaxy for anomalous (e.g., spinning) dust as well as synchrotron emission. We find the dust opacity in the solar neighbourhood, τ/N_H = 0.92 ± 0.05 × 10^-25   cm² at 250 μm, with no significant variation with Galactic radius, even though the dust temperature is seen to vary from over 25 K to under 14 K. Furthermore, we show that anomalous dust emission is present in the atomic, molecular and dark gas phases throughout the Galactic disk. Anomalous emission is not clearly detected in the ionised phase, as free-free emission is seen to dominate. The derived dust propeties associated with the dark gas phase are derived but do not allow us to reveal the nature of this phase. For all environments, the anomalous emission is consistent with rotation from polycyclic aromatic hydrocarbons (PAHs) and, according to our simple model, accounts for (25 ± 5)% (statistical) of the total emission at 30 GHz.