Star formation scaling relations at ∼100 pc from PHANGS: Impact of completeness and spatial scale

¹ Max-Planck-Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: pessa@mpia.de
² INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
³ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁴ Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
⁵ Max-Planck-Institute for Extraterrestrial Physics, Giessenbachstraße 1, 85748 Garching, Germany
⁶ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, 69120 Heidelberg, Germany
⁷ Departamento de Astronomía, Universidad de Chile, Santiago, Chile
⁸ Observatories of the Carnegie Institution for Science, Pasadena, CA, USA
⁹ Departamento de Física de la Tierra y Astrofísica, Universidad Complutense de Madrid, 28040 Madrid, Spain
¹⁰ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
¹¹ Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071, USA
¹² Department of Astronomy, University of Massachusetts – Amherst, 710 N. Pleasant Street, Amherst, MA 01003, USA
¹³ Universität Heidelberg, Zentrum für Astronomie, Institut für theoretische Astrophysik, Albert-Ueberle-Straße 2, 69120 Heidelberg, Germany
¹⁴ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
¹⁵ Observatorio Astronómico Nacional (IGN), C/Alfonso XII, 3, 28014 Madrid, Spain
¹⁶ Centro de Desarrollos Tecnológicos, Observatorio de Yebes (IGN), 19141 Yebes, Guadalajara, Spain
¹⁷ Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Im Neuenheimer Feld 205, 69120 Heidelberg, Germany
¹⁸ Center for Astrophysics ∣ Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA
¹⁹ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
²⁰ Institut de Radioastronomie Millimétrique (IRAM), 300 Rue de la Piscine, 38406 Saint Martin d’Hères, France
²¹ Department of Physics, University of Alberta, Edmonton, AB T6G 2E1, Canada

Received: 5 March 2021
Accepted: 18 April 2021

Abstract

Aims. The complexity of star formation at the physical scale of molecular clouds is not yet fully understood. We investigate the mechanisms regulating the formation of stars in different environments within nearby star-forming galaxies from the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) sample.

Methods. Integral field spectroscopic data and radio-interferometric observations of 18 galaxies were combined to explore the existence of the resolved star formation main sequence (Σ_stellar versus Σ_SFR), resolved Kennicutt–Schmidt relation (Σ_mol. gas versus Σ_SFR), and resolved molecular gas main sequence (Σ_stellar versus Σ_mol. gas), and we derived their slope and scatter at spatial resolutions from 100 pc to 1 kpc (under various assumptions).

Results. All three relations were recovered at the highest spatial resolution (100 pc). Furthermore, significant variations in these scaling relations were observed across different galactic environments. The exclusion of non-detections has a systematic impact on the inferred slope as a function of the spatial scale. Finally, the scatter of the Σ_{mol. gas + stellar} versus Σ_SFR correlation is smaller than that of the resolved star formation main sequence, but higher than that found for the resolved Kennicutt–Schmidt relation.

Conclusions. The resolved molecular gas main sequence has the tightest relation at a spatial scale of 100 pc (scatter of 0.34 dex), followed by the resolved Kennicutt–Schmidt relation (0.41 dex) and then the resolved star formation main sequence (0.51 dex). This is consistent with expectations from the timescales involved in the evolutionary cycle of molecular clouds. Surprisingly, the resolved Kennicutt–Schmidt relation shows the least variation across galaxies and environments, suggesting a tight link between molecular gas and subsequent star formation. The scatter of the three relations decreases at lower spatial resolutions, with the resolved Kennicutt–Schmidt relation being the tightest (0.27 dex) at a spatial scale of 1 kpc. Variation in the slope of the resolved star formation main sequence among galaxies is partially due to different detection fractions of Σ_SFR with respect to Σ_stellar.