The volumetric star formation law in nearby galaxies

TL;DR

This paper introduces a volumetric star formation law based on intrinsic volume densities of gas and SFR in nearby galaxies, providing a more fundamental relation than surface density laws.

Contribution

It derives a new volumetric star formation law by converting surface densities into volume densities using galaxy disc thickness inferred from hydrostatic equilibrium.

Findings

A tight correlation between volume densities of gas and SFR was found.

The volumetric law has significant implications for understanding star formation physics.

It offers a more fundamental relation than traditional surface density laws.

Abstract

Star formation laws are empirical relations between the cold gas (HI+H$_2$) content of a galaxy and its star formation rate (SFR), being crucial for any model of galaxy formation and evolution. A well known example of such laws is the Schmidt-Kennicutt law, which is based on the projected surface densities. However, it has been long unclear whether a more fundamental relation exists between the intrinsic volume densities. By assuming the vertical hydrostatic equilibrium, we infer radial profiles for the thickness of gaseous discs in a sample of 23 local galaxies, and use these measurements to convert the observed surface densities of the gas and the SFR into the de-projected volume densities. We find a tight correlation linking these quantities, that we call the volumetric star formation law. This relation and its properties have crucial implications for our understanding of the physics of star formation.