Variations in the Σ_SFR − Σ_mol − Σ_⋆ plane across galactic environments in PHANGS galaxies

¹ Max-Planck-Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: pessa@mpia.de
² Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
³ Center for Astrophysics, Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA
⁴ Department of Physics, University of Alberta, Edmonton, AB T6G 2E1, Canada
⁵ Department of Physics, Tamkang University, No. 151, Yingzhuan Rd., Tamsui Dist., New Taipei City 251301, Taiwan
⁶ Max-Planck-Institute for Extraterrestrial Physics, Giessenbachstraße 1, 85748 Garching, Germany
⁷ Observatorio Astronómico Nacional (IGN), C/Alfonso XII, 3, 28014 Madrid, Spain
⁸ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
⁹ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
¹⁰ Observatories of the Carnegie Institution for Science, Pasadena, CA, USA
¹¹ Departamento de Astronomía, Universidad de Chile, Santiago, Chile
¹² Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, 69120 Heidelberg, Germany
¹³ Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071, USA
¹⁴ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
¹⁵ Univ. Lyon, Univ. Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69230 Saint-Genis-Laval, France
¹⁶ Institute for Computational Science, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
¹⁷ Universität Heidelberg, Zentrum für Astronomie, Institut für theoretische Astrophysik, Albert-Ueberle-Straße 2, 69120 Heidelberg, Germany
¹⁸ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
¹⁹ International Centre for Radio Astronomy Research University of Western Australia, 7 Fairway, Crawley, WA 6009, Australia
²⁰ Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Im Neuenheimer Feld 205, 69120 Heidelberg, Germany
²¹ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
²² Institut de Radioastronomie Millimétrique (IRAM), 300 Rue de la Piscine, 38406 Saint Martin d’Hères, France
²³ LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, 75014 Paris, France
²⁴ Departamento de Física de la Tierra y Astrofísica, Universidad Complutense de Madrid, 28040 Madrid, Spain

Received: 3 December 2021
Accepted: 21 March 2022

Abstract

Aims. There exists some consensus that the stellar mass surface density (Σ_⋆) and molecular gas mass surface density (Σ_mol) are the main quantities responsible for locally setting the star formation rate. This regulation is inferred from locally resolved scaling relations between these two quantities and the star formation rate surface density (Σ_SFR), which have been extensively studied in a wide variety of works. However, the universality of these relations is debated. Here, we probe the interplay between these three quantities across different galactic environments at a spatial resolution of 150 pc.

Methods. We performed a hierarchical Bayesian linear regression to find the best set of parameters C_⋆, C_mol, and C_norm that describe the star-forming plane conformed by Σ_⋆, Σ_mol, and Σ_SFR, such that logΣ_SFR = C_⋆logΣ_⋆ + C_mollogΣ_mol + C_norm. We also explored variations in the determined parameters across galactic environments, focusing our analysis on the C_⋆ and C_mol slopes.

Results. We find signs of variations in the posterior distributions of C_⋆ and C_mol across different galactic environments. The dependence of Σ_SFR on Σ_⋆ spans a wide range of slopes, with negative and positive values, while the dependence of Σ_SFR on Σ_mol is always positive. Bars show the most negative value of C_⋆ (−0.41), which is a sign of longer depletion times, while spiral arms show the highest C_⋆ among all environments (0.45). Variations in C_mol also exist, although they are more subtle than those found for C_⋆.

Conclusions. We conclude that systematic variations in the interplay of Σ_⋆, Σ_mol, and Σ_SFR across different galactic environments exist at a spatial resolution of 150 pc, and we interpret these variations to be produced by an additional mechanism regulating the formation of stars that is not captured by either Σ_⋆ or Σ_mol. Studying environmental variations in single galaxies, we find that these variations correlate with changes in the star formation efficiency across environments, which could be linked to the dynamical state of the gas that prevents it from collapsing and forming stars, or to changes in the molecular gas fraction.