Schmidt-Kennicutt relations in SPH simulations of disc galaxies with effective thermal feedback from supernovae

TL;DR

This study uses advanced SPH simulations with stellar feedback to analyze the Schmidt-Kennicutt relations in spiral galaxies, revealing environmental dependencies and proposing a new pressure model that aligns with observed star formation behaviors.

Contribution

It introduces a novel feedback implementation in simulations and demonstrates a new pressure relation that better explains star formation in galaxy discs.

Findings

The SK relation steepens at low gas surface densities depending on gas fraction.

Molecular gas-based SK relation shows less variation across simulations.

A new pressure fit better describes disc pressure than classical models.

Abstract

We study several versions of the Schmidt-Kennicutt (SK) relation obtained for isolated spiral galaxies in TreeSPH simulations run with the GADGET3 code including the novel MUlti-Phase Particle Integrator (MUPPI) algorithm for star formation and stellar feedback. [...] The standard SK relation between surface densities of cold (neutral+molecular) gas and star formation rate of simulated galaxies shows a steepening at low gas surface densities, starting from a knee whose position depends on disc gas fraction: for more gas-rich discs the steepening takes place at higher surface densities. Because gas fraction and metallicity are typically related, this environmental dependence mimics the predictions of models where the formation of H2 is modulated by metallicity. The cold gas surface density at which HI and molecular gas surface densities equate can range from ~10 up to 34 Msun/pc^2. As expected, the SK relation obtained using molecular gas shows much smaller variations among simulations. We find that disc pressure is not well represented by the classical external pressure of a disc in vertical hydrostatic equilibrium. Instead is well fit by the expression P_fit = Sigma_cold sigma_cold kappa / 6, where the three quantities on the right-hand side are cold gas surface density, vertical velocity dispersion and epicyclic frequency. When the "dynamical" SK relation, i.e. the relation that uses gas surface density divided by orbital time, is considered, we find that all of our simulations stay on the same relation. We interpret this as a manifestation of the equilibrium between energy injection and dissipation in stationary galaxy discs, when energetic feedback is effective and pressure is represented by the expression given above. These findings further support the idea that a realistic model of the structure of galaxy discs should take into account energy injection by SNe. [Abridged]