Speaker
Description
The cold gas in galaxies shows continuous turbulent motions occurring at various spatial scales that exceed those associated with thermal motions, as inferred from the observed HI velocity dispersions, implying a need for a continuous source of energy input. Supernova (SN) feedback is considered to be one of the primary candidates for this, because of its substantial energy output, consistency, and widespreadness. However, past studies have shown that while SNe possibly contribute to the observed kinetic energies, it cannot account for all of the observed turbulent motions, especially in the regions with low star formation rate (SFR), such as the outskirts of spiral galaxies and dwarfs. Despite consideration of other energy injection mechanisms, the observed turbulence has remained unknown for a long time. Yet, a recent study of nearby spiral galaxies partially resolved this conundrum by considering the increase in gas disc thickness with radius (i.e. flaring of the galactic disc), slowing down the rate of dissipation. Consequently, less energy is needed from the SN feedback, allowing it to maintain turbulence in spirals with modest efficiencies.
In my talk, I present new results on the role of SN feedback in driving the neutral atomic gas (HI) turbulence in nearby dwarf galaxies. I use the HI distribution and kinematics of a sample of 14 dwarfs in the LITTLE-THINGS survey, and UV photometric data from GALEX to derive, respectively, the HI kinetic energy and the distribution of SNe across the galaxy discs. I use the HI disc thickness, calculated assuming the hydrostatic equilibrium, to derive the turbulence dissipation time. Using Bayesian hierarchical modeling, I show that a simple model of SN-driven turbulence can explain the observed HI kinetic energies with just $\sim 2 - 3\%$ of the total SN energy, while assuming some contribution from the warm HI thermal energies. My results hold even while considering a larger sample representative of galaxies on the star-forming main sequence, from dwarfs to massive spirals. In conclusion, my results provide: 1) empirical evidence that SNe alone can sustain the observed turbulence in regions of low SFR and 2) the first direct estimate of a potentially universal SN efficiency common to all main-sequence galaxies, offering particularly valuable constraints for sub-grid models of SN feedback in numerical simulations of galaxy evolution.