Timescales on which star formation affects the neutral interstellar medium

Turbulent neutral hydrogen (H I) line widths are often thought to be driven primarily by star formation (SF), but the timescale for converting SF energy to H I kinetic energy is unclear. As a complication, studies on the connection between H I line widths and SF in external galaxies often use broadband tracers for the SF rate, which must implicitly assume that SF histories (SFHs) have been constant over the timescale of the tracer. In this paper, we compare measures of H I energy to time-resolved SFHs in a number of nearby dwarf galaxies. We find that H I energy surface density is strongly correlated only with SF that occurred 30-40 Myr ago. This timescale corresponds to the approximate lifetime of the lowest mass supernova progenitors (∼8 MO). This analysis suggests that the coupling between SF and the neutral interstellar medium is strongest on this timescale, due either to an intrinsic delay between the release of the peak energy from SF or to the coherent effects of many supernova explosions during this interval. At Σ_SFR > 10^-3 MO yr ^-1 kpc^-2, we find a mean coupling efficiency between SF energy and H I energy of ε = 0.11 ± 0.04 using the 30-40 Myr timescale. However, unphysical efficiencies are required in lower Σ_SFR systems, implying that SF is not the primary driver of H I kinematics at Σ_SFR < 10^-3 Mo yr^-1 kpc^-2.