Astron. Astrophys. Suppl. Ser.
Volume 133, Number 3, December II 1998
|Page(s)||337 - 352|
|Published online||15 December 1998|
Studies of dense molecular cores in regions of massive star formation*
VII. Core properties on the galactic scale
Institute of Applied Physics of the Russian Academy of Sciences, 46 Uljanov str., 603600 Nizhny Novgorod, Russia
2 Helsinki University Observatory, Tähtitorninmäki, P.O. Box 14, FIN-00014 University of Helsinki, Finland
Send offprint request to: I. Zinchenko
Accepted: 18 June 1998
We surveyed 55 northern non-stellar H2O ma s ers in the CS line with the 20-m Onsala radio telescope and detected 47 CS cores associated probably with 50 masers. The CS emission for this sample is weaker on the average than for the similar southern sample studied by us earlier at SEST. Most of the detected cores were mapped in CS. The CS peaks were observed also in the C34S and in the CO lines. We present CS maps as well as CO, CS and, when available, C34S spectra for the 26 best studied cores. From the CS maps and optically thin C34S emission we derive the basic physical parameters of the cores: size, LTE mass, mean density, virial mass. Combining the present results with the previous SEST data we obtain statistical distributions of the core parameters. The CO brightness temperature distribution for most cores ranges from ~15 K to ~50 K with a peak at 20 - 30 K. The typical sizes of the cores are pc. The mean density lies in the range 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 . The CS line widths are highly supersonic ( km s-1). We analyze the dependences of these parameters on galactocentric distance R. The mean density of the cores drops with increasing R in the interval kpc. It is consistent with an exponential law with a scale length of 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 probably explained 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 km s-1.
Key words: stars: formation / ISM: clouds / ISM: molecules / radio lines: interstellar
Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or via http://cdsweb.u-strasbg.fr/Abstract.html
© European Southern Observatory (ESO), 1998