We study the star formation ( SF ) law in 12 Galactic molecular clouds with ongoing high-mass star formation ( HMSF ) activity , as traced by the presence of a bright IRAS source and other HMSF tracers .
We define the molecular cloud ( MC ) associated to each IRAS source using ^ { 13 } CO line emission , and count the young stellar objects ( YSOs ) within these clouds using GLIMPSE and MIPSGAL 24 \mu m Spitzer databases .
The masses for high luminosity YSOs ( L _ { bol } > 10 L _ { \odot } ) are determined individually using Pre Main Sequence evolutionary tracks and the evolutionary stages of the sources , whereas a mean mass of 0.5 M _ { \odot } was adopted to determine the masses in the low luminosity YSO population .
The star formation rate surface density ( \Sigma _ { SFR } ) corresponding to a gas surface density ( \Sigma _ { gas } ) in each MC is obtained by counting the number of the YSOs within successive contours of ^ { 13 } CO line emission .
We find a break in the relation between \Sigma _ { SFR } and \Sigma _ { gas } , with the relation being power-law ( \Sigma _ { SFR } \propto \Sigma _ { gas } ^ { N } ) with the index N varying between 1.4 and 3.6 above the break .
The \Sigma _ { gas } at the break is between 150–360 M _ { \odot } ~ { } { pc } ^ { -2 } for the sample clouds , which compares well with the threshold gas density found in recent studies of Galactic star-forming regions .
Our clouds treated as a whole lie between the Kennicutt ( 1998 ) relation and the linear relation for Galactic and extra-galactic dense star-forming regions .
We find a tendency for the high-mass YSOs to be found preferentially in dense regions at densities higher than 1200 M _ { \odot } ~ { } { pc } ^ { -2 } ( \sim 0.25 ~ { } g~ { } cm ^ { -2 } ) .