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 ( \sim 8 \mathrm { M } _ { \odot } ) .
This analysis suggests that the coupling between SF and the neutral ISM 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 SNe during this interval .
At \Sigma _ { \mathrm { SFR } } { } > 10 ^ { -3 } \mathrm { M } _ { \odot } yr ^ { -1 } kpc ^ { -2 } , we find a mean coupling efficiency between SF energy and H i energy of \epsilon = 0.11 \pm 0.04 using the 30 - 40 Myr timescale .
However , unphysical efficiencies are required in lower \Sigma _ { \mathrm { SFR } } systems , implying that SF is not the primary driver of H i kinematics at \Sigma _ { \mathrm { SFR } } { } < 10 ^ { -3 } \mathrm { M } _ { \odot } yr ^ { -1 } kpc ^ { -2 } .