The small and the beautiful: How the star formation law affects galactic disk structure

TL;DR

This study evaluates how different star formation laws influence the structure of galactic disks in simulations, finding that multi free-fall models align well with observations, while some outdated models produce unrealistic clumpy disks.

Contribution

It compares various analytical star formation parameterizations in high-resolution simulations, highlighting the importance of multi free-fall models for realistic galactic disk structures.

Findings

Multi free-fall models match observed star formation rates.

Obsolete models lead to overly clumpy disks.

Single free-fall models produce less realistic structures.

Abstract

We investigate the influence of different analytical parameterizations and fit functions for the local star formation rate in AMR simulations of an isolated disk galaxy with the Nyx code. Such parameterizations express the star formation efficiency as function of the local turbulent Mach number and virial parameter. By employing the method of adaptively refined large eddy simulations, we are able to evaluate these physical parameters from the numerically unresolved turbulent energy associated with the grid scale. We consider both single and multi free-fall variants of star formation laws proposed by Padoan & Nordlund, Hennebelle & Chabrier, and Krumholz & McKee, summarised and tested recently with numerical simulations by Federrath & Klessen. We find that the global star formation rate and the relation between the local star formation rate and the gas column density is reproduced in agreement with observational constraints by all multi free-fall models of star formation. Some models with obsolete calibration or a single free-fall time scale, however, result in an overly clumpy disk that does not resemble the structure of observed spirals.