Astronomy:Kennicutt–Schmidt law

Short description: Astronomical trend of star formation

In astronomy, the Kennicutt–Schmidt law is an empirical relation between the surface gas density and star formation rate (SFR) in a given region. 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 [math]\displaystyle{ n }[/math] of the local gas surface density. i.e.

[math]\displaystyle{ \Sigma_{SFR} \propto (\Sigma_{gas})^n }[/math].

In general, the SFR surface density [math]\displaystyle{ (\Sigma_{SFR}) }[/math] is in units of solar masses per year per square parsec [math]\displaystyle{ (M_\odot ~\textrm{ yr}^{-1} \textrm{ pc}^{-2}) }[/math] and the gas surface density in grams per square parsec [math]\displaystyle{ (\textrm{g}~\textrm{pc}^{-2}) }[/math]. 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 [math]\displaystyle{ n \approx 2 }[/math] (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[math]\displaystyle{ \alpha }[/math] intensities in a sample of 15 galaxies could be fit with the earlier Schmidt relations with a power law index of [math]\displaystyle{ n = 1.3 \pm 0.3 }[/math]. More recently, he examined the connection between surface gas density and SFR for a larger set of galaxies to estimate a value of [math]\displaystyle{ n = 1.4 \pm 0.15 }[/math].