Search for High-Mass Protostellar Objects in Cold IRAS Sources
  We present the results of CS J=2-1 mapping observations towards 39 massive
star-forming regions selected from the previous CO line survey of cold IRAS
sources with high-velocity CO flows along the Galactic plane (Yang et al.
2002). All sources are detected in CS J=2-1 showing the existence of CS clumps
around the IRAS sources. However, one-third of the sources are not deeply
embedded in the dense clumps by comparison of the central powering IRAS sources
and the morphologies of CS clumps. Physical parameters of the dense molecular
clumps are presented. We have identified 12 high-mass protostellar object
(HMPO) candidates by checking the association between the dense cores and the
IRAS sources, the detection of water maser, and the radio properties towards
the IRAS sources. We find that the HMPO sources are characterized by low FIR
luminosity to virial mass ratios since they are in very early evolutionary
stages when the massive protostars have not reached their full luminosities,
which are typical for zero-age main sequence stars. Large turbulent motion in
the HMPO sources may be largely due to the large kinetic energy ejected by the
central protostars formed in the dense clumps. However, alternative means or
undetected outflows may also be responsible for the turbulence in the clumps.
