Physical properties of molecular clouds as functions of their Galactocentric distance from CS and C34S observations

Abstract

Twenty-eight CS molecular clouds toward HII regions with Galactocentric distances from ∼ 4 to 20 kpc have been studied based on observations obtained in the J=2→1 lines of CS and C34S on the 20-meter radio telescope of the Onsala Space Observatory (Sweden) in March 2001. All 28 clouds have been mapped with an angular resolution of ∼40″. The peak intensity in the C34S line has been measured for 20 objects. An LTE analysis has been performed and the parameters of the molecular cloud cores derived. The core sizes are dA=0.3–4.8 pc, with a median value of ∼1.6 pc. The mean hydrogen densities in the cloud cores are nH2=3.5×102–3.7 × 104 cm−3, with a median value of ∼7.2×103 cm−3. The value of nH2 ends to decrease with increasing Galactocentric distance of the cloud. The masses of most clouds are 102−6×103M⊙, with the most probable value being MCS∼103M⊙. The data follow the dependence MCS ∝d A (2.4–3.2) . As a rule, the cloud masses are lower than the virial masses for MCS<103M⊙.