Scaling Relations between Gas and Star Formation in Nearby Galaxies

TL;DR

This study investigates the relationship between gas surface densities and star formation rates in nearby galaxies at high resolution, revealing distinct regimes and a nearly constant molecular gas depletion time in star-forming disks.

Contribution

It provides detailed, high-resolution analysis of gas-SFR relations across different galactic environments, highlighting the constancy of molecular gas depletion time and the varying role of HI and H2.

Findings

Sigma_H2 correlates strongly with Sigma_SFR

Molecular gas depletion time is about 2 Gyr in large spirals

Sigma_SFR scales with Sigma_HI in outer galaxy regions

Abstract

High resolution, multi-wavelength maps of a sizeable set of nearby galaxies have made it possible to study how the surface densities of HI, H2 and star formation rate (Sigma_HI, Sigma_H2, Sigma_SFR) relate on scales of a few hundred parsecs. At these scales, individual galaxy disks are comfortably resolved, making it possible to assess gas-SFR relations with respect to environment within galaxies. Sigma_H2, traced by CO intensity, shows a strong correlation with Sigma_SFR and the ratio between these two quantities, the molecular gas depletion time, appears to be constant at about 2Gyr in large spiral galaxies. Within the star-forming disks of galaxies, Sigma_SFR shows almost no correlation with Sigma_HI. In the outer parts of galaxies, however, Sigma_SFR does scale with Sigma_HI, though with large scatter. Combining data from these different environments yields a distribution with multiple regimes in Sigma_gas - Sigma_SFR space. If the underlying assumptions to convert observables to physical quantities are matched, even combined datasets based on different SFR tracers, methodologies and spatial scales occupy a well define locus in Sigma_gas - Sigma_SFR space.