Kennicutt–Schmidt law

In astronomy, the Kennicutt–Schmidt law (or simply Schmidt law) is an empirical relation between the 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 ${\displaystyle n}$ of the local gas surface density.^[1] i.e.

${\displaystyle \Sigma _{SFR}\propto (\Sigma _{gas})^{n}}$.

In general, the SFR surface density ${\displaystyle (\Sigma _{SFR})}$ is in units of solar masses per year per square parsec ${\displaystyle (M_{\odot }~{\textrm {yr}}^{-1}{\textrm {pc}}^{-2})}$ and the gas surface density in grams per square parsec ${\displaystyle ({\textrm {g}}~{\textrm {pc}}^{-2})}$. 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 ${\displaystyle n\approx 2}$ (and very likely between 1 and 3). All of the data used were gathered from the Milky Way, and specifically the solar-neighborhood.

In 1998, Robert Kennicutt found that the H${\displaystyle \alpha }$ intensities of every galaxy in a sample of 7 could be fit with the Schmidt law.^[2] More recently, he examined the connection between gas density and SFR for nearly 100 nearby galaxies to estimate a value of ${\displaystyle n=1.4\pm 0.15}$.^[3]

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