Stellar structures, molecular gas, and star formation across the PHANGS sample of nearby galaxies^⋆

¹ Observatorio Astronómico Nacional (IGN), C/ Alfonso XII 3, 28014 Madrid, Spain
e-mail: m.querejeta@oan.es
² Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
³ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
⁴ Department of Astronomy, The Ohio State University, 140 West 18th Ave, Columbus, OH 43210, USA
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 Universität Heidelberg, Zentrum für Astronomie, Albert-Ueberle-Straße 2, 69120 Heidelberg, Germany
⁸ Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, INF 205, 69120 Heidelberg, Germany
⁹ Space Physics and Astronomy Research Unit, University of Oulu, Pentti Kaiteran katu 1, 90014, Finland
¹⁰ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
¹¹ The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101, USA
¹² Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
¹³ Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstraße 12-14, 69120 Heidelberg, Germany
¹⁴ Department of Physics & Astronomy, University of Wyoming, Laramie, WY 82071, USA
¹⁵ Department of Astronomy, University of Massachusetts Amherst, 710 North Pleasant St., Amherst, MA 01003, USA
¹⁶ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
¹⁷ IRAM, 300 Rue de la Piscine, 38406 Saint Martin d’Hères, France
¹⁸ CNRS, IRAP, 9 Av. du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
¹⁹ Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse Cedex 4, France
²⁰ NRAO, 520 Edgemont Road, Charlottesville, VA 22903, USA
²¹ Sorbonne Université, Observatoire de Paris, Université PSL, CNRS, LERMA, 75005 Paris, France
²² University of Alberta, 4-183 CCIS, Edmonton, Alberta, Canada
²³ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße 1, 85748 Garching, Germany

Received: 1 March 2021
Accepted: 24 August 2021

Abstract

We identify stellar structures in the PHANGS sample of 74 nearby galaxies and construct morphological masks of sub-galactic environments based on Spitzer 3.6 μm images. At the simplest level, we distinguish five environments: centres, bars, spiral arms, interarm regions, and discs without strong spirals. Slightly more sophisticated masks include rings and lenses, which are publicly released but not explicitly used in this paper. We examine trends with environment in the molecular gas content, star formation rate, and depletion time using PHANGS–ALMA CO(2–1) intensity maps and tracers of star formation. The interarm regions and discs without strong spirals clearly dominate in area, whereas molecular gas and star formation are quite evenly distributed among the five basic environments. We reproduce the molecular Kennicutt–Schmidt relation with a slope compatible with unity within the uncertainties and without significant slope differences among environments. In contrast to what has been suggested by early studies, we find that bars are not always deserts devoid of gas and star formation, but instead they show large diversity. Similarly, spiral arms do not account for most of the gas and star formation in disc galaxies, and they do not have shorter depletion times than the interarm regions. Spiral arms accumulate gas and star formation, without systematically boosting the star formation efficiency. Centres harbour remarkably high surface densities and on average shorter depletion times than other environments. Centres of barred galaxies show higher surface densities and wider distributions compared to the outer disc; yet, depletion times are similar to unbarred galaxies, suggesting highly intermittent periods of star formation when bars episodically drive gas inflow, without enhancing the central star formation efficiency permanently. In conclusion, we provide quantitative evidence that stellar structures in galaxies strongly affect the organisation of molecular gas and star formation, but their impact on star formation efficiency is more subtle.