Statistics of high-velocity outflows in regions of massive star formation

Based on a SO and C¹⁸O survey of dense molecular-cloud cores in regions of massive star formation (selected by the presence of H₂O maser emission), we estimate the frequency of occurrence of high-velocity outflows in these regions and their parameters. The presence of extended SO-line wings (compared to C¹⁸O) is considered to be indicative of outflows. We estimate the outflow parameters (mass, momentum, and kinetic energy) from optically thin C¹⁸O lines, which increases the reliability of these estimates. According to this approach, high-velocity outflows were detected in ～40% of the observed objects, which is a lower limit on the frequency of their occurrence. There is a clear correlation between the outflow mass, momentum, and kinetic energy, on the one hand, and the bolometric luminosity of the associated infrared sources, on the other hand. The slope of the correlations is close to unity. Their comparison with similar correlations of the mass-loss rate, force, and mechanical luminosity with the bolometric luminosity shows that the spread in outflow dynamical age is small and that this age has no systematic correlation with the infrared luminosity. The mean outflow dynamical age that can be obtained from this comparison is ～7×10¹³ yr.