The star formation law in Galactic high-mass star-forming molecular
  clouds
  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 13CO line emission, and count the young
stellar objects (YSOs) within these clouds using GLIMPSE and MIPSGAL 24 micron
Spitzer databases.The masses for high luminosity YSOs (Lbol>10~Lsun) are
determined individually using Pre Main Sequence evolutionary tracks and the
evolutionary stages of the sources, whereas a mean mass of 0.5 Msun was adopted
to determine the masses in the low luminosity YSO population. The star
formation rate surface density (sigsfr) corresponding to a gas surface density
(siggas) in each MC is obtained by counting the number of the YSOs within
successive contours of 13CO line emission. We find a break in the relation
between sigsfr and siggas, with the relation being power-law (sigsfr ~
siggas^N) with the index N varying between 1.4 and 3.6 above the break. The
siggas at the break is between 150-360 Msun/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
Msun/pc^2 (~0.25 g/cm^2).
