Kavli Affiliate: Nickolay Y. Gnedin
| First 5 Authors: Ava Polzin, Andrey V. Kravtsov, Vadim A. Semenov, Nickolay Y. Gnedin,
| Summary:
We analyze high-resolution hydrodynamics simulations of an isolated disk
dwarf galaxy with an explicit model for unresolved turbulence and
turbulence-based star formation prescription. We examine the characteristic
values of the star formation efficiency per free-fall time,
$epsilon_mathrm{ff}$, and its variations with local environment properties,
such as metallicity, UV flux, and surface density. We show that the star
formation efficiency per free-fall time in $approx 10$ pc star-forming regions
of the simulated disks has values in the range $epsilon_mathrm{ff}approx
0.01-0.1$, similar to observational estimates, with no trend with metallicity
and only a weak trend with the UV flux. Likewise, $epsilon_{rm ff}$ estimated
using projected patches of 500 pc size does not vary with metallicity and shows
only a weak trend with average UV flux and gas surface density. The
characteristic values of $epsilon_mathrm{ff}approx 0.01-0.1$ arise naturally
in the simulations via the combined effect of dynamical gas compression and
ensuing stellar feedback that injects thermal and turbulent energy. The
compression and feedback regulate the virial parameter, $alpha_mathrm{vir}$,
in star-forming regions, limiting it to $alpha_mathrm{vir}approx 3-10$.
Turbulence plays an important role in the universality of
$epsilon_mathrm{ff}$ because turbulent energy and its dissipation are not
sensitive to metallicity and UV flux that affect thermal energy. Our results
indicate that the universality of observational estimates of
$epsilon_mathrm{ff}$ can be plausibly explained by the turbulence-driven and
feedback-regulated properties of star-forming regions.
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