Metallicity Dependence of Pressure-Regulated Feedback-Modulated Star Formation in the TIGRESS-NCR Simulation Suite

Abstract

We present a new simulation suite for the star-forming interstellar medium (ISM) in galactic disks using the TIGRESS-NCR framework. Distinctive aspects of our simulation suite are: (1) sophisticated and comprehensive numerical treatments of essential physical processes including magnetohydrodynamics, self-gravity, and galactic differential rotation, as well as photochemistry, cooling, and heating coupled with ray-tracing UV radiation transfer and resolved supernova feedback and (2) wide parameter coverage including metallicity over $Z^{\prime }\equiv Z/Z_{\odot }\sim 0.1-3$, gas surface density ${\Sigma }_{\mathrm{gas}}\sim 5-150M_{\odot }\mathrm{p}{\mathrm{c}}^{-2}$, and stellar surface density ${\Sigma }_{\mathrm{star}}\sim 1-50M_{\odot }\mathrm{p}{\mathrm{c}}^{-2}$. The range of emergent star formation rate surface density is ${\Sigma }_{\mathrm{SFR}}\sim 10^{-4}-0.5M_{\odot }\mathrm{kp}{\mathrm{c}}^{-2}\mathrm{y}{\mathrm{r}}^{-1}$ and ISM total midplane pressure is $P_{\mathrm{tot}}/k_B=10^3-10^6\mathrm{c}{\mathrm{m}}^{-3}\mathrm{K}$, with $P_{\mathrm{tot}}$ equal to the ISM weight $W$. For given ${\Sigma }_{\mathrm{gas}}$ and ${\Sigma }_{\mathrm{star}}$, we find ${\Sigma }_{\mathrm{SFR}}\propto Z^{\prime 0.3}$. We provide an interpretation based on the pressure-regulated feedback-modulated (PRFM) star formation theory. We characterize feedback modulation in terms of the yield ${\rm Y}$, defined as the ratio of each stress to ${\Sigma }_{\mathrm{SFR}}$. The thermal feedback yield varies sensitively with both weight and metallicity as ${{\rm Y}}_{\mathrm{th}}\propto W^{-0.46}{Z}^{\prime -0.53}$, while the combined turbulent and magnetic feedback yield shows weaker dependence ${{\rm Y}}_{\mathrm{turb}+\mathrm{mag}}\propto W^{-0.22}{Z}^{\prime -0.18}$. The reduction in ${\Sigma }_{\mathrm{SFR}}$ at low metallicity is due mainly to enhanced thermal feedback yield, resulting from reduced attenuation of UV radiation. With the metallicity-dependent calibrations we provide, PRFM theory can be used for a new subgrid star formation prescription in cosmological simulations where the ISM is unresolved.

Resubmitted to ApJ after minor revision