Interpreting millimeter emission from IMEGIN galaxies NGC 2146 and NGC 2976

¹ Institute for Research in Fundamental Sciences (IPM), School of Astronomy, Tehran, Iran
² Institut d’Astrophysique de Paris, Sorbonne Université, CNRS (UMR7095), 98 bis Boulevard Arago, 75014 Paris, France
³ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
⁴ School of Physics and Astronomy, Cardiff University, Queen’s Buildings, The Parade, Cardiff CF24 3AA, UK
⁵ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
⁶ Université Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, 38000 Grenoble, France
⁷ Max Planck Institute for Extraterrestrial Physics, Giessenbach-strasse 1, 85748 Garching, Germany
⁸ University of Ghent, Department of Physics and Astronomy, Ghent, Belgium
⁹ Aix Marseille Univ., CNRS, CNES, LAM (Laboratoire d’Astrophysique de Marseille), Marseille, France
¹⁰ Université Grenoble Alpes, CNRS, Institut, Néel, France
¹¹ Institut de RadioAstronomie Millimétrique (IRAM), Grenoble, France
¹² Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 5, I-00185 Roma, Italy
¹³ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹⁴ Centro de Astrobiología (CSIC-INTA), Torrejón de Ardoz, 28850 Madrid, Spain
¹⁵ Institut d’Astrophysique Spatiale (IAS), CNRS, Université Paris Sud, Orsay, France
¹⁶ IRAP, Université de Toulouse, CNRS, UPS, IRAP, Toulouse Cedex 4, France
¹⁷ National Observatory of Athens, Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, Ioannou Metaxa and Vasileos Pavlou, GR-15236 Athens, Greece
¹⁸ Department of Astrophysics, Astronomy & Mechanics, Faculty of Physics, University of Athens, Panepistimiopolis, GR-15784 Zografos, Athens, Greece
¹⁹ High Energy Physics Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439, USA
²⁰ Instituto de Radioastronomía Milimétrica (IRAM), Granada, Spain
²¹ LERMA, Observatoire de Paris, PSL Research Univ., CNRS, Sorbonne Univ., UPMC, 75014 Paris, France
²² School of Earth and Space Exploration and Department of Physics, Arizona State University, Tempe, AZ 85287, USA
²³ STAR Institute, Université de Liège, Quartier Agora, Allée du Six Aout 19c, B-4000 Liege, Belgium
²⁴ Sterrenkundig Observatorium Universiteit Gent, Krijgslaan 281 S9, B-9000 Gent, Belgium
²⁵ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
²⁶ Laboratoire de Physique de l’École Normale Supérieure, ENS, PSL Research University, CNRS, Sorbonne Université, Université de Paris, 75005 Paris, France
²⁷ Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104, USA
²⁸ University of Lyon, UCB Lyon 1, CNRS/IN2P3, IP2I, 69622 Villeurbanne, France
²⁹ Dipartimento di Fisica, Università di Roma ‘Tor Vergata’, Via della Ricerca Scientifica 1, I-00133 Roma, Italy

^⋆ Corresponding author; gejlali@ipm.ir

Received: 26 February 2024
Accepted: 10 October 2024

Abstract

The millimeter continuum emission from galaxies provides important information about cold dust, its distribution, its heating, and its role in the interstellar medium (ISM). This emission also carries an unknown portion of the free-free and synchrotron radiation. The IRAM 30 m Guaranteed Time Large Project, Interpreting Millimeter Emission of Galaxies with IRAM and NIKA2 (IMEGIN) provides a unique opportunity to study the origin of the millimeter emission at angular resolutions of < 18″ in a sample of nearby galaxies. As a pilot study, we present millimeter observations of two IMEGIN galaxies, NGC 2146 (starburst) and NGC 2976 (peculiar dwarf) at 1.15 mm and 2 mm. Combined with the data taken with the Spitzer, Herschel, Planck, WSRT, and the 100 m Effelsberg telescopes, we modeled the infrared-to-radio Spectral Energy Distribution (SED) of these galaxies, both globally and at resolved scales, using a Bayesian approach to (1) dissect different components of the millimeter emission, (2) investigate the physical properties of dust, and (3) explore the correlations between millimeter emission, gas, and star formation rate (SFR). We find that cold dust is responsible for most of the 1.15 mm emission in both galaxies and at 2 mm in NGC 2976. The free-free emission emits more importantly in NGC 2146 at 2 mm. The cold dust emissivity index is flatter in the dwarf galaxy (β = 1.3 ± 0.1) compared to the starburst galaxy (β = 1.7 ± 0.1). Mapping the dust-to-gas ratio, we find that it changes between 0.004 and 0.01 with a mean of 0.006 ± 0.001 in the dwarf galaxy. In addition, there is no global balance between the formation and dissociation of H₂ in this galaxy. We find tight correlations between the millimeter emission and both the SFR and molecular gas mass in both galaxies.