The Global Schmidt Law in Star‐forming Galaxies

TLDR

The study combines Hα, H I, and CO measurements from 61 normal spirals with far‑infrared and CO data from 36 starbursts to investigate the global star‑formation law across a wide range of gas densities and SFRs. The authors compile disk‑averaged SFRs and gas densities from these multi‑wavelength observations to test the Schmidt law and an alternative orbital‑time scaling relation. The combined sample follows a Schmidt law with index N = 1.4 ± 0.15, a tight relation spanning several orders of magnitude, and the orbital‑time scaling also fits well, providing useful recipes for galaxy‑formation simulations.

Abstract

Measurements of Hα, H I, and CO distributions in 61 normal spiral galaxies are combined with published far-infrared and CO observations of 36 infrared-selected starburst galaxies, in order to study the form of the global star formation law over the full range of gas densities and star formation rates (SFRs) observed in galaxies. The disk-averaged SFRs and gas densities for the combined sample are well represented by a Schmidt law with index N = 1.4 ± 0.15. The Schmidt law provides a surprisingly tight parametrization of the global star formation law, extending over several orders of magnitude in SFR and gas density. An alternative formulation of the star formation law, in which the SFR is presumed to scale with the ratio of the gas density to the average orbital timescale, also fits the data very well. Both descriptions provide potentially useful "recipes" for modeling the SFR in numerical simulations of galaxy formation and evolution.