Re-visiting the extended Schmidt law: the important role of existing stars in regulating star formation

TL;DR

This study confirms that the extended Schmidt law, which links star formation efficiency to stellar surface density, holds across diverse galactic environments and even for outliers, emphasizing the role of existing stars in star formation regulation.

Contribution

The paper provides spatially-resolved evidence that the extended Schmidt law applies broadly, highlighting the influence of existing stars on star formation regulation across various galactic conditions.

Findings

Star formation regions follow a tight power-law relation involving stellar and gas surface densities.

The extended Schmidt law applies to low-density outer disks and outliers, including metal-poor regions.

Existing stars significantly influence star formation through gravitational effects on mid-plane pressure.

Abstract

We revisit the proposed extended Schmidt law (Shi et al. 2011) which points that the star formation efficiency in galaxies depends on the stellar mass surface density, by investigating spatially-resolved star formation rates (SFRs), gas masses and stellar masses of star formation regions in a vast range of galactic environments, from the outer disks of dwarf galaxies to spiral disks and to merging galaxies as well as individual molecular clouds in M33. We find that these regions are distributed in a tight power-law as Sigma_SFR ~(Sigma_star^0.5 Sigma_gas )^1.09, which is also valid for the integrated measurements of disk and merging galaxies at high-z. Interestingly, we show that star formation regions in the outer disks of dwarf galaxies with Sigma_SFR down to 10^(-5) Msun/yr/kpc^2, which are outliers of both Kennicutt-Schmidt and Silk-Elmegreen law, also follow the extended Schmidt law. Other outliers in the Kennicutt-Schmidt law, such as extremely-metal poor star-formation regions, also show significantly reduced deviations from the extended Schmidt law. These results suggest an important role for existing stars in helping to regulate star formation through the effect of their gravity on the mid-plane pressure in a wide range of galactic environments.