Simulating nearby disc galaxies on the main star formation sequence

II. The gas structure transition in low and high stellar mass discs

¹ Excellence Cluster ORIGINS, Boltzmannstraße 2 85748 Garching, Germany
² European Southern Observatory, Karl-Schwarzschild-Straße 2 85748 Garching, Germany
³ Univ Lyon, Univ Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69230, Saint-Genis-Laval, France
⁴ Observatoire Astronomique de Strasbourg, Université de Strasbourg, CNRS UMR 7550, F-67000 Strasbourg, France
⁵ University of Strasbourg Institute for Advanced Study, 5 allée du Général Rouvillois F-67083, Strasbourg, France
⁶ Lund Observatory, Division of Astrophysics, Department of Physics, Lund University, Box 43 SE-221 00 Lund, Sweden
⁷ Astronomy Unit, Department of Physics, University of Trieste, Via Tiepolo 11 I-34131, Trieste, Italy
⁸ INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11 I-34131, Trieste, Italy
⁹ ICSC – Italian Research Center on High Performance Computing, Big Data and Quantum Computing, Via Magnanelli 40033 Casalecchio di Reno (BO), Italy
¹⁰ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9 B-9000, Gent, Belgium
¹¹ Max Planck Institut für Astronomie, Königstuhl 17 69117 Heidelberg, Germany
¹² Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2 D-69120, Heidelberg, Germany
¹³ Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Im Neuenheimer Feld 205 D-69120, Heidelberg, Germany
¹⁴ Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA, USA
¹⁵ Elizabeth S. and Richard M. Cashin Fellow at the Radcliffe Institute for Advanced Studies at Harvard University, 10 Garden Street, Cambridge, MA 02138, USA
¹⁶ Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071, USA
¹⁷ SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
¹⁸ Sub-department of Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK

^⋆ Corresponding author.

Received: 6 February 2025
Accepted: 5 May 2025

Abstract

Recent hydrodynamical simulations of isolated barred disc galaxies have suggested a structural change in the distribution of the interstellar medium (ISM) around a stellar mass M_* of 10¹⁰ M_⊙. In the higher-mass regime (M_∗ ≥ 10¹⁰ M_⊙), we observe the formation of a central gas and stellar disc with a typical size of a few hundred parsecs connected through lanes to the ends of the stellar bar. In the lower-mass regime (M_∗ < 10¹⁰ M_⊙), such an inner disc is absent and the gas component exhibits a more chaotic distribution. Observations of nearby star-forming galaxies support the existence of such a change. These inner gas discs may represent an important intermediate scale connecting the large kiloparsec-scale structures with the nuclear (sub-parsec) region, transporting gas inwards to fuel the central supermassive black hole (SMBH). For this work we used an extended set of high-resolution hydrodynamical simulations of isolated disc galaxies with initial properties (i.e. stellar mass, gas fraction, stellar disc scale length, and the bulge mass fraction) with properties covering the range of galaxies in the PHANGS sample to investigate this change of regime. We studied the physical properties of the star-forming ISM in both stellar mass regimes and extracted a few physical tracers: the inner Lindblad resonance (ILR), the probability distribution function (PDF), the virial parameter, and the Mach number. In line with observations, we confirm a structure transition in the simulations that occurs between a stellar mass of 10^9.5 and 10¹⁰ M_⊙. We show that the physical origin of this change of regime is driven by stellar feedback and its contribution relative to the underlying gravitational potential. With their shallower potential and typically higher gas mass fraction, lower-mass disc PHANGS galaxies combine two ingredients that significantly delay or even prevent the formation of a central gas (and stellar) disc. These results shed some light on the observed properties of star-forming barred galaxies and have implications for the star formation regimes, the growth of central structures, and the overall secular evolution of disc galaxies.