Observations of interstellar carbon monosulfide: evidence for turbulent cores in giant molecular clouds

We have observed lines of CS(J=1..-->..0) and CS(J=2..-->..1) with nearly equal beam sizes and high velocity resolution in 32 molecular sources including a variety of source types. We find that, with a few exceptions, these two transitions show nearly equal intensities and line widths. Peak corrected antenna temperatures typically fall in the range of 1--5 K or about one-tenth of the corresponding CO intensities, and CS line widths are seen to be approximately one-half those of CO. In general the profiles are symmetrical and singly peaked with Gaussian or triangular line shapes. We find CS half-intensity cloud dimensions of 1'--5' or approximately 25% of the corresponding CO cloud dimensions.Hydrogen densities and CS fractional abundances derived from our data using a velocity gradient radiative transfer model are seen to be in good agreement with the same quantities obtained from the microturbulent model of Liszt and Leung. Values obtained for n (H/sub 2/) and X (CS/dv/dr range from 2 x 10/sup 4/ to 2 x 10/sup 5/ cm/sup -3/ and 3 x 10/sup -11/ to 3 x 10/sup -10/ (Km s/sup -1/pc/sup -1/)/sup -1/, respectively. Values for the (J=2..-->..1) optical depths obtained from radiative transfer modeling and other independent arguments fall inmore » the range 0.3--3.0, indicating that mild saturation effects can be expected for some CS lines.While the CS data alone can be interpreted satisfactorily in the context of a microturbulent model, we feel that a cloud model also capable of describing the excitation and distribution of other molecules must involve density and large-scale velocity gradients such has that discussed by Kwan. However, the equal line widths and similar profiles observed in the CS(J=1..-->..0) and CS(J=2..-->..1) transitions then require that the CS fractional abundance decrease with increasing cloud radius so that the CS lines are derived principally from a turbulent core.« less