Astronomy and Astrophysics, volume 301, 236-260 (1995/9-1)
IRAS sources beyond the solar circle. VI. Analysis of the FIR, H2O, and CO emission.
WOUTERLOOT J.G.A., FIEGLE K., BRAND J. and WINNEWISSER G.
Abstract (from CDS):
For a sample of 1357 IRAS sources with FIR colours of young stellar objects we have compared the occurrence and properties of H2O maser- and 12CO(1-0) emission with the observed and derived IRAS parameters. We find that the distribution of differences between the CO and H2O velocities is a Gaussian with a FWHM of about 11km/s. The mean velocity difference is nearly zero. The velocity of the peak H2O emission is not at a preferred location within the velocity interval where emission is detected. The H2O maser detection rate increases with both the FIR luminosity and the 12CO(1-0) line width: below log(LFIR/L☉)=3.5, less than 10% of the sources show maser emission, whereas H2O is detected towards almost all of the sources above log(LFIR/L☉)=4.5. For the sources with H2O maser emission, the average CO line width (FWHM about 5.0km/s) is approximately twice as large as for those without detected H2O emission, an effect which is independent of the sources' FIR luminosity. However a significant fraction of sources with no detected H2O emission still have line widths larger than 1.9km/s, the median value for the quiescent gas not associated with the IRAS sources. The maximum H2O maser luminosity at each FIR luminosity is proportional to LFIR: LH2O/L☉=10–7.4(LFIR/L☉). In IRAS colour-colour plots, sources can be distinguished in maser-like and non-maser-like sources according to their CO line widths and FIR luminosity. At a given LFIR the maximum T*A found for 12CO(1-0) decreases with distance from the Sun, likely due to beam filling effects. Few sources with maser emission have T*A below 7.5K, when observed with the IRAM 30-m telescope. There is no difference in the maximum T*A of sources with maser-like and non-maser-like IRAS colours. We have derived the intrinsic luminosity- and mass distribution of sources with (non)-maser-like IRAS colours, correcting for incompleteness effects at lower luminosities. The slope of the IMF for sources with maser-like colours and mass larger than 10M☉ is found to be -2.8±0.3.
masers - stars: pre-main sequence - ISM: molecules - infrared: ISM: continuum - radio lines: ISM
erratum vol. 319, p. 360
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