CSOLOGO1 CSOLOGO2Studying massive star forming clumps at the CSO



  Most stars in our Galaxy, including all massive stars,  form in Giant Molecular Cloud (GMC) clumps.
These clumps are very massive (several thousands of solar mass), dense (number density of about 106 cm-3),
and highly obscured by dust.  They can only be explored by dust continuum emission or molecular emission
lines of dense gas tracers like Hydrogen cyanide (HCN) and Carbon monosulfide (CS).  Astronomers led by
Dr. Jingwen Wu at Harvard-Smithsonian Center for Astrophysics have used the CSO and another radio
telescope at Five College Radio Astronomy Observatory (FCRAO) to map more than fifty such massive
clumps in the Milky Way, with multiple HCN and CS transitions.   Figure 1 presents the contour maps of
one of these massive clumps obtained at the CSO and FCRAO. They have studied their properties revealed
by the dense gas, including their mass, size, luminosity, volume density, and dynamics. They also found
these clumps are centrally condensed, very turbulent, and many may be experiencing collapse.

   Astronomers conclude that the most relevant  parameter for their star formation rate is the total mass of dense gas
the clumps contain. They found all dense gas tracers show a linear correlation between their star formation rate
(indicated by their infrared luminosity)  and the total amount of dense gas, a relationship similar
to that found in galaxies (as shown in Figure 2). The physical reason underlying this correlation may be that
star formation in GMC has a threshold in terms of the mass of dense gas.  These GMC clumps may be building
blocks of galaxies.  The results were published by Wu et al. 2010 in the Astrophysical Journal Supplement Series.



Figure 1. Contour maps of one massive dense clump (G10.6-0.4) with several HCN and CS lines.



Figure 2. Linear correlation exists between the infrared luminosity and the line luminosity (for all
dense gas tracers) for Galactic massive clumps that brighter than 104.5 Lsun; Some correlations
extend to galaxy scales (the dots at the right side in the panels).

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