Radial variations of the volume and surface star formation laws in the Galaxy

Variation of the volume and surface Schmidt laws (star formation or SF law) with the galacto-centric distance R was investigated using 3D distributions of H II regions, H I, and molecular (H₂) gases in the Milky Way. Both the power-law index and SF coefficient were found to vary with R. The index is flatter in the inner disc than in the outer Galaxy, and the coefficient is larger in the inner disc, decreasing steeply outwardly. There is also a mutual anti-correlation between the index and SF coefficient, and the SF law can be expressed by a single-parameter function of the SF coefficient. The variable SF law is discussed in relation to self-regulation of SF.