From the CS maps and optically thin C34S emission we have derived the basic physical parameters of the cores: size, LTE mass, mean density, virial mass. Combining the present results with the previous SEST data we obtained statistical distributions of the core parameters. The CO brightness temperature for most cores lies in the range 15- 50 K with a peak at 20-30 K. The size of most cores is 1.0-1.5 pc. The mean density lies in the range 103-105 cm-3 which is much lower than densities needed for CS excitation from multitransitional analysis. The slope of the mass spectrum for is . The ratio of the IR luminosity of associated IRAS point sources to mass peaks at 10 .The CS line widths are highly supersonic (1.5-9 kms-1).
We have analysed the dependences of these parameters on galactocentric distance R. The mean density of the cores decreases with increasing R in agreement with an exponential law with a scale length of kpc in the interval kpc. The IR luminosity to mass ratio changes probably in a similar way. The core size increases with R in accordance with the density decrease and constant mass.
The comparison of the CS and C34S data shows almost no broadening of the CS lines due to optical depth effects. This can be explained probably by small scale clumpiness in the cores. The velocity difference between the CS cores and H2O masers is close to zero on the average with the standard deviation of 7 kms-1.
We are very grateful to Dr. Lars E.B. Johansson for his help with the observations and for obtaining important additional data, to Prof. Kalevi Mattila for critical reading of the manuscript and to an anonymous referee for valuable suggestions. I.Z. and L.P. thank the Helsinki University Observatory for the hospitality during the data reduction and the paper preparation stages. They were also supported in part by the INTAS grant 93-2168-ext and grant 96-02-16472 from the Russian Foundation for Basic Research. This research has made use of the Simbad database, operated at CDS, Strasbourg, France.
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