The Star Formation Law in Atomic and Molecular Gas

TL;DR

This paper presents a theoretical model linking star formation rates to interstellar radiation, molecular cloud properties, and feedback-driven turbulence, successfully matching observed correlations across different galaxy environments.

Contribution

It introduces a unified star formation law based on physical processes governing molecular gas formation and feedback effects, improving understanding of galaxy star formation.

Findings

Predicted star formation rates agree with observed correlations.

Model explains the role of metallicity and gas surface densities.

Provides a framework connecting molecular cloud physics to galaxy-scale star formation.

Abstract

We propose a simple theoretical model for star formation in which the local star formation rate in a galaxy is determined by three factors. First, the interplay between the interstellar radiation field and molecular self-shielding determines what fraction of the gas is in molecular form and thus eligible to form stars. Second, internal feedback determines the properties of the molecular clouds that form, which are nearly independent of galaxy properties until the galactic ISM pressure becomes comparable to the internal GMC pressure. Above this limit, galactic ISM pressure determines molecular gas properties. Third, the turbulence driven by feedback processes in GMCs makes star formation slow, allowing a small fraction of the gas to be converted to stars per free-fall time within the molecular clouds. We combine analytic estimates for each of these steps to formulate a single star formation law, and show that the predicted correlation between star formation rate, metallicity, and surface densities of atomic, molecular, and total gas agree well with observations.