Quantifying the energy balance between the turbulent ionised gas and young stars

¹ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
e-mail: oleg.egorov@uni-heidelberg.de
² Institüt für Theoretische Astrophysik, Zentrum für Astronomie der Universität Heidelberg, Albert-Ueberle-Strasse 2, 69120 Heidelberg, Germany
³ International Centre for Radio Astronomy Research, University of Western Australia, 7 Fairway, Crawley 6009 WA, Australia
⁴ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50157 Firenze, Italy
⁵ European Southern Observatory, Karl-Schwarzschild Straße 2, 85748 Garching bei München, Germany
⁶ Univ. Lyon, Univ. Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69230 Saint-Genis-Laval, France
⁷ Interdisziplinäres Zentrum für Wissenschaftliches Rechnen der Universität Heidelberg, Im Neuenheimer Feld 205, 69120 Heidelberg, Germany
⁸ Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, Ohio 43210, USA
⁹ Center for Cosmology and Astroparticle Physics, 191 West Woodruff Avenue, Columbus, OH 43210, USA
¹⁰ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
¹¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹³ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
¹⁴ European Southern Observatory (ESO), Alonso de Córdova 3107, Casilla 19, Santiago 19001, Chile
¹⁵ Department of Physics & Astronomy, University of Wyoming, Laramie, WY 82071, USA
¹⁶ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
¹⁷ AURA for the European Space Agency (ESA), Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁸ Gemini Observatory/NSF’s NOIRLab, 950 N. Cherry Avenue, Tucson, AZ, USA
¹⁹ Steward Observatory, University of Arizona, 933 N Cherry Ave, Tucson, AZ 85721, USA
²⁰ Department of Physics & Astronomy, Bloomberg Center for Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
²¹ Sub-department of Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK

Received: 16 May 2023
Accepted: 17 August 2023

Abstract

Context. Stellar feedback is a key contributor to the morphology and dynamics of the interstellar medium in star-forming galaxies. In particular, energy and momentum input from massive stars can drive the turbulent motions in the gas, but the dominance and efficiency of this process are unclear. The study of ionised superbubbles enables quantitative constraints to be placed on the energetics of stellar feedback.

Aims. We directly compare the kinetic energy of expanding superbubbles and the turbulent motions in the interstellar medium with the mechanical energy deposited by massive stars in the form of winds and supernovae. With such a comparison, we aim to determine whether the stellar feedback is responsible for the observed turbulent motions and to quantify the fraction of mechanical energy retained in the superbubbles.

Methods. We investigated the ionised gas morphology, excitation properties, and kinematics in 19 nearby star-forming galaxies from the PHANGS-MUSE survey. Based on the distribution of the flux and velocity dispersion in the Hα line, we selected 1484 regions of locally elevated velocity dispersion (σ(Hα) > 45 km s⁻¹), including at least 171 expanding superbubbles. We analysed these regions and related their properties to those of the young stellar associations and star clusters identified in PHANGS-HST data.

Results. We find a good correlation between the kinetic energy of the ionised gas and the total mechanical energy input from supernovae and stellar winds from the stellar associations. At the same time, the contribution of mechanical energy injected by the supernovae alone is not sufficient to explain the measured kinetic energy of the ionised gas, which implies that pre-supernova feedback in the form of radiation and thermal pressure as well as winds is necessary. We find that the gas kinetic energy decreases with metallicity for our sample covering Z = 0.5 − 1.0 Z_⊙, reflecting the lower impact of stellar feedback. For the sample of well-resolved superbubbles, we find that about 40% of the young stellar associations are preferentially located in their rims. We also find a slightly higher (by ∼15%) fraction of the youngest (< 3 Myr) stellar associations in the rims of the superbubbles than in the centres and the opposite trend for older associations, which implies possible propagation or triggering of star formation.

Conclusions. Stellar feedback is the dominant source for powering the ionised gas in regions of locally (on a 50–500 pc scale) elevated velocity dispersion, with a typical coupling efficiency of 10 − 20%. Accounting for pre-supernovae feedback is required to set up the energy balance between gas and stars.