Kennicutt–Schmidt law explained

In astronomy, the Kennicutt–Schmidt law is an empirical relation between the surface gas density and star formation rate (SFR) in a given region.^[1] The relation was first examined by Maarten Schmidt in a 1959 paper where he proposed that the SFR surface density scales as some positive power

n of the local gas surface density. i.e.\Sigma _{SFR} \propto (\Sigma _{gas} ) ^{n} .

In general, the SFR surface density

(\Sigma _{SFR} ) is in units of solar masses per year per square parsec (M _{\odot} ~ rm{ yr} ^{-1} rm{ pc} ^{-2} ) and the gas surface density in grams per square parsec ( rm{g}~ rm{pc} ^{-2} ) . Using an analysis of gaseous helium and young stars in the solar neighborhood, the local density of white dwarfs and their luminosity function, and the local helium density, Schmidt suggested a value of n ≈ 2 (and very likely between 1 and 3). All of the data used were gathered from the Milky Way, and specifically the solar neighborhood.

In 1989, Robert Kennicutt found that the H

\alpha intensities in a sample of 15 galaxies could be fit with the earlier Schmidt relations with a power law index of n = 1 . 3 \pm 0 . 3 . More recently, he examined the connection between surface gas density and SFR for a larger set of galaxies to estimate a value of n = 1 . 4 \pm 0 . 15 .

Notes and References

1. The name "Schmidt law" is now commonly used for a general relation between volume gas density and star formation rate, and the Kennicutt-Schmidt law for the surface gas density and star formation rate.