The stratification of ISM properties in the edge-on galaxy NGC 891 revealed by NIKA2

¹ National Observatory of Athens, Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, Ioannou Metaxa and Vasileos Pavlou, 15236 Athens, Greece
e-mail: s.katsioli@noa.gr
² Department of Astrophysics, Astronomy & Mechanics, Faculty of Physics, University of Athens, Panepistimiopolis, 15784 Zografos, Athens, Greece
³ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38400 Saint-Martin-d’Hères, France
⁴ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
⁵ Cardiff Hub for Astrophysics Research & Technology, School of Physics & Astronomy, Cardiff University, Queens Buildings, Cardiff CF24 3AA, UK
⁶ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
⁷ Univ. Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, 53, avenue des Martyrs, 38000 Grenoble, France
⁸ Max Planck Institute for Extraterrestrial Physics, Giessenbach-strasse 1, 85748 Garching, Germany
⁹ Sterrenkundig Observatorium Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
¹⁰ Aix-Marseille Univ., CNRS, CNES, LAM (Laboratoire d’Astrophysique de Marseille), Marseille, France
¹¹ Institut Néel, CNRS, Université Grenoble Alpes, Saint-Martin-d’Hères, France
¹² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹³ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
¹⁴ Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185 Roma, Italy
¹⁵ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹⁶ Institute for Research in Fundamental Sciences (IPM), Larak Garden, 19395-5531 Tehran, Iran
¹⁷ Centro de Astrobiología (CSIC-INTA), Torrejón de Ardoz, 28850 Madrid, Spain
¹⁸ IRAP, Université de Toulouse, CNRS, UPS, IRAP, 9 Avenue colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
¹⁹ Université Paris-Saclay, CNRS, Institut d’astrophysique spatiale, 91405 Orsay, France
²⁰ High Energy Physics Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439, USA
²¹ Instituto de Radioastronomía Milimétrica (IRAM), Granada, Spain
²² LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC, 75014 Paris, France
²³ School of Earth and Space Exploration and Department of Physics, Arizona State University, Tempe, AZ 85287, USA
²⁴ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
²⁵ Laboratoire de Physique de l’École Normale Supérieure, ENS, PSL Research University, CNRS, Sorbonne Université, Université de Paris 75005 Paris, France
²⁶ INAF-Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, Italy
²⁷ Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104, USA
²⁸ Institut d’Astrophysique de Paris, Sorbonne Université, CNRS (UMR7095), 75014 Paris, France
²⁹ University of Lyon, UCB Lyon 1, CNRS/IN2P3, IP2I, 69622 Villeurbanne, France

Received: 26 May 2023
Accepted: 31 July 2023

Abstract

Context. As the millimeter wavelength range remains a largely unexplored spectral region for galaxies, the IMEGIN large program aims to map the millimeter continuum emission of 22 nearby galaxies at 1.15 and 2 mm.

Aims. Using the high-resolution maps produced by the NIKA2 camera, we explore the existence of very cold dust and take possible contamination by free–free and synchrotron emission into account. We study the IR-to-radio emission coming from different regions along the galactic plane and at large vertical distances.

Methods. New observations of NGC 891, using the NIKA2 camera on the IRAM 30 m telescope, along with a suite of observations at other wavelengths were used to perform a multiwavelength study of the spectral energy distribution in the interstellar medium in this galaxy. This analysis was performed globally and locally, using the advanced hierarchical Bayesian fitting code, HerBIE, coupled with the THEMIS dust model.

Results. Our dust modeling is able to reproduce the near-IR to millimeter emission of NGC 891, with the exception of an excess at a level of 25% obtained by the NIKA2 observations in the outermost parts of the disk. The radio continuum and thermal dust emission are distributed differently in the disk and galaxy halo. Different dusty environments are also revealed by a multiwavelength investigation of the emission features. Our detailed decomposition at millimeter and centimeter wavelengths shows that emission at 1 mm is purely originated by dust. Radio components become progressively important with increasing wavelengths. Finally, we find that emission arising from small dust grains accounts for ∼9.5% of the total dust mass, reaching up to 20% at large galactic latitudes. Shock waves in the outflows that shatter the dust grains might explain this higher fraction of small grains in the halo.

Conclusions. NIKA2 observations have proven essential for a complete characterization of the interstellar medium in NGC 891. They have been critical to separate the dust, free–free, and synchrotron emission in the various emitting regions within the galaxy.