Continuum, CO, and water vapour maps of the Orion Nebula

First millimetre spectral imaging with CONCERTO

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
² Univ. Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, 53, avenue des Martyrs, 38000 Grenoble, France
³ Aix Marseille Univ, CNRS, CNES, LAM (Laboratoire d’Astrophysique de Marseille), Marseille, France
⁴ Institut Néel, CNRS, Université Grenoble Alpes, France
⁵ Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, 67000 Strasbourg, France
⁶ European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching, Germany
⁷ Institut de Radioastronomie Millimétrique (IRAM), Avenida Divina Pastora 7, Local 20, 18012 Granada, Spain
⁸ Institut de RadioAstronomie Millimétrique (IRAM), Grenoble, France
⁹ Instituto de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretaña 1111, Valparaíso, Chile
¹⁰ Millennium Nucleus for Galaxies (MINGAL)
¹¹ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
¹² School of Physics and Astronomy, Cardiff University, Queen’s Buildings, The Parade, Cardiff, CF24 3AA, UK
¹³ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
¹⁴ Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185 Roma, Italy
¹⁵ Institute for Research in Fundamental Sciences (IPM), School of Astronomy, Tehran, Iran
¹⁶ Centro de Astrobiología (CSIC-INTA), Torrejόn de Ardoz, 28850 Madrid, Spain
¹⁷ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
¹⁸ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
¹⁹ Department of Physics and Astronomy, University of the Western Cape, Robert Sobukhwe Road, Bellville 7535, South Africa
²⁰ National Observatory of Athens, Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, Ioannou Metaxa and Vasileos Pavlou 15236, Athens, Greece
²¹ Department of Astrophysics, Astronomy & Mechanics, Faculty of Physics, University of Athens, Panepistimiopolis, 15784 Zografos, Athens, Greece
²² High Energy Physics Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439, USA
²³ LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC, 75014 Paris, France
²⁴ Institute of Space Sciences (ICE), CSIC, Campus UAB, Carrer de Can Magrans s/n, 08193 Barcelona, Spain
²⁵ ICREA, Pg. Lluís Companys 23, Barcelona, Spain
²⁶ IRAP, CNRS, Université de Toulouse, CNES, UT3-UPS, ( Toulouse), France
²⁷ Dipartimento di Fisica, Università di Roma ‘Tor Vergata’, Via della Ricerca Scientifica 1, 00133 Roma, Italy
²⁸ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
²⁹ Institut d’Astrophysique de Paris, CNRS (UMR7095), 98 bis boulevard Arago, 75014 Paris, France
³⁰ University of Lyon, UCB Lyon 1, CNRS/IN2P3, IP2I, 69622 Villeurbanne, France

^★ Corresponding author.

Received: 28 April 2025
Accepted: 28 July 2025

Abstract

Context. The millimetre spectrum of Galactic regions and galaxies is rich in continuum and molecular lines. This diversity is mostly explored using either broad-band photometry or high-resolution heterodyne spectroscopy.

Aims. We aim to map the millimetre continuum emission of Galactic regions with an intermediate spectral resolution between broadband photometry and heterodyne spectroscopy, enabling us to rapidly cover large sky areas with spectroscopy.

Methods. We report observations of the Orion Nebula with the CONCERTO instrument, which was installed at the APEX telescope focal plane from 2021 to 2023.

Results. We find that the spectrum of Orion is dominated by dust emission with an emissivity index ranging between 1.3 and 2.0, along with strong CO(2-1) and H₂O lines, which are naturally separated from the continuum due to the CONCERTO spectral capabilities. Many regions also show strong free-free emission at lower frequencies.

Conclusions. We demonstrate the spectral capabilities of CONCERTO at intermediate spectral resolution, with a frequency coverage from 130 to 310 GHz. A sensitivity of 200 mK is achieved in one second, for one beam and a 6 GHz frequency width, over an 18 arcmin diameter field of view, which is within a factor of three of the expectations. We show that we can spectrally disentangle the continuum from the CO line emission, but the line is not resolved at a resolution of ~8000 km s^–1. The slope of the millimetre continuum is line-free mapped for the first time in Orion.