Indications of a sub-linear and non-universal Kennicutt-Schmidt relationship

TL;DR

This study uses hierarchical Bayesian analysis to estimate the Kennicutt-Schmidt relationship in nearby galaxies, revealing that the relationship varies across galaxies and is not universal, challenging existing star formation models.

Contribution

It introduces a hierarchical Bayesian method to accurately estimate the KS parameters, demonstrating the non-universality of the relationship across different galaxies.

Findings

KS slope varies between 0.58 and 0.94 across galaxies

Molecular gas depletion time is not constant and increases with Sigma_mol

Other galactic properties influence star formation rates

Abstract

We estimate the parameters of the Kennicutt-Schmidt (KS) relationship, linking the star formation rate (Sigma_SFR) to the molecular gas surface density (Sigma_mol), in the STING sample of nearby disk galaxies using a hierarchical Bayesian method. This method rigorously treats measurement uncertainties, and provides accurate parameter estimates for both individual galaxies and the entire population. Assuming standard conversion factors to estimate Sigma_SFR and Sigma_mol from the observations, we find that the KS parameters vary between galaxies, indicating that no universal relationship holds for all galaxies. The KS slope of the whole population is 0.76, with the 2sigma range extending from 0.58 to 0.94. These results imply that the molecular gas depletion time is not constant, but varies from galaxy to galaxy, and increases with the molecular gas surface density. Therefore, other galactic properties besides just Sigma_mol affect Sigma_SFR, such as the gas fraction or stellar mass. The non-universality of the KS relationship indicates that a comprehensive theory of star formation must take into account additional physical processes that may vary from galaxy to galaxy.