The gas morphology of nearby star-forming galaxies

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: stuber@mpia.de
² Sub-department of Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
³ Observatorio Astronómico Nacional (IGN), C/Alfonso XII 3, Madrid 28014, Spain
⁴ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
⁵ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁶ Univ. Lyon, Univ. Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69230 Saint-Genis-Laval, France
⁷ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁸ Universität Heidelberg, Zentrum für Astronomie, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
⁹ Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Im Neuenheimer Feld 205, 69120 Heidelberg, Germany
¹⁰ Department of Astronomy, The Ohio State University, 140 West 18th Ave, Columbus, OH 43210, USA
¹¹ Cosmic Origins Of Life (COOL) Research DAO, coolresearch.io
¹² Department of Physics & Astronomy, University of Wyoming, Laramie, WY 82071, USA
¹³ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
¹⁴ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
¹⁵ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße 1, 85748 Garching, Germany
¹⁶ Department of Physics, Tamkang University, No. 151, Yingzhuan Road, Tamsui District, New Taipei City 251301, Taiwan
¹⁷ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁸ Department of Physics, University of Connecticut, Storrs, CT 06269, USA
¹⁹ IRAM, 300 rue de la Piscine, 38400 Saint-Martin-d’Hères, France
²⁰ LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, 75014 Paris, France

Received: 3 March 2023
Accepted: 19 May 2023

Abstract

A galaxy’s morphology stems from the secular and environmental processes taking place over the course of its evolutionary history. Thus, it has consistently served as an important tool for gaining insights into galaxy evolution. In this work, we visually classified morphologies on cloud-scales based on the molecular gas distribution of a large sample of 79 nearby main sequence galaxies, using 1″ resolution CO(2–1) ALMA observations taken as part of the PHANGS survey. For this purpose, we devised a morphology classification scheme for different types of bars, spiral arms (grand-design, flocculent, multi-arm and smooth), and rings (central and non-central rings) that are similar to the well established optical ones. Furthermore, we introduced bar lane classes. In general, our cold gas-based morphologies is in good agreement with the ones based on stellar light. Both of our bars, as well as the grand-design spiral arms, are preferentially found at the higher mass end of our sample. Our gas-based classification indicates a potential for a misidentification of unbarred galaxies in the optical when massive star formation is present. Central or nuclear rings are present in a third of the sample, with a strong preference seen for barred galaxies (59%). As stellar bars are present in 45 ± 5% of our sample galaxies, we explore the utility of molecular gas as tracer of bar lane properties. We find that more curved bar lanes have a shorter radial extent in molecular gas and reside in galaxies with lower molecular to stellar mass ratios than those with straighter geometries. Galaxies display a wide range of CO morphologies and this work is aimed at providing a catalogue of morphological features in a representative sample of nearby galaxies.