Metallicity Dependence of Pressure-regulated Feedback-modulated Star Formation in the TIGRESS-NCR Simulation Suite

Abstract

We present a new suite of numerical simulations of 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 direct ray-tracing UV radiation transfer and resolved supernova feedback and (2) wide parameter coverage including the variation in metallicity over $Z^{\prime} \equiv Z/{Z}_{\odot }\sim 0.1-3$ , gas surface density Σ _gas ∼ 5–150 M _⊙ pc ^−2 , and stellar surface density Σ _star ∼ 1–50 M _⊙ pc ^−2 . The range of emergent star formation rate surface density is Σ _SFR ∼ 10 ^−4 –0.5 M _⊙ kpc ^−2 yr ^−1 , and ISM total midplane pressure is P _tot / k _B = 10 ^3 –10 ^6 cm ^−3 K, with P _tot equal to the ISM weight ${ \mathcal W }$ . For given Σ _gas and Σ _star , we find ${{\rm{\Sigma }}}_{\mathrm{SFR}}\propto Z{{\prime} }^{0.3}$ . We provide an interpretation based on the pressure-regulated feedback-modulated (PRFM) star formation theory. The total midplane pressure consists of thermal, turbulent, and magnetic stresses. We characterize feedback modulation in terms of the yield ϒ, defined as the ratio of each stress to Σ _SFR . The thermal feedback yield varies sensitively with both weight and metallicity as ${{\rm{\Upsilon }}}_{\mathrm{th}}\propto {{ \mathcal W }}^{-0.46}Z{{\prime} }^{-0.53}$ , while the combined turbulent and magnetic feedback yield shows weaker dependence ${{\rm{\Upsilon }}}_{\mathrm{turb}+\mathrm{mag}}\propto {{ \mathcal W }}^{-0.22}Z{{\prime} }^{-0.18}$ . The reduction in Σ _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.

Keywords

• Interstellar medium
• Star formation
• Magnetohydrodynamical simulations
• Stellar feedback
• Metallicity
• Galaxy formation