A `universal' supernova efficiency to drive the HI turbulence in nearby star-forming galaxies

Abstract

The origin of cold gas turbulence in galaxies has been extensively debated. Supernovae (SNe), the dominant form of stellar feedback, were thought insufficient to sustain it against dissipation, especially in galactic environments with low star formation rates (SFRs). In this work, we investigate the origin of the neutral atomic gas (HI) turbulence in dwarf irregular galaxies, a challenging regime of low masses and SFRs. We built on a recent study of spirals showing that disc flaring prolongs the dissipation timescale, reducing the energy needed to sustain turbulence and making SN feedback viable. We measured the SN efficiency, which is the fraction of SN energy required to sustain HI turbulence in 14 dwarfs, and tested whether a universal efficiency holds across a sample representative of the star-forming main sequence. From the observed HI distributions and kinematics, we derived the radial profiles of the HI kinetic energy per unit area and modelled them as the sum of thermal energy and turbulent energy from SNe, constrained by the observed SFR surface density. We considered pure cold and warm neutral medium (WNM) phases as limiting cases, as well as a mixed two-phase scenario, obtaining the SN efficiency and WNM fraction via hierarchical Bayesian inference. We found that the observed HI kinetic energy in dwarfs requires only łesssim 3% of the SN energy, and that a universal efficiency of ≈ 2% explains the HI turbulence across our main sequence sample. Our findings suggest that the SN efficiency remains similar across galaxies with different properties, offering valuable constraint for feedback recipes in galaxy evolution models.