The cold, massive molecular cloud G216-2.5. 2: Structure and kinematics

Details The cold, massive molecular cloud G216-2.5. 2: Structure and kinematics The cold, massive molecular cloud G216-2.5. 2: Structure and kinematics

Sep 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...432..167l&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 432, no. 1, p. 167-180

Astronomy and Astrophysics

Astronomy

19

Carbon Monoxide, Dynamic Characteristics, Emission Spectra, Interstellar Matter, Kinematics, Line Spectra, Molecular Clouds, Radio Astronomy, Radio Spectra, Extremely High Frequencies, Local Thermodynamic Equilibrium, Mass, Millimeter Waves, Star Formation, Velocity Distribution

Scientific paper

We have studied the gas properties and kinematics of G216-2.5 (also called Maddalena's cloud), a cold, massive giant molecular cloud (GMC) with no obvious signs of star formation. We have mapped 11 square degrees of the cloud in the J = 1 goes to 0 transitions of (12)CO and (13)CO using the QUARRY 15 beam array receiver on the 14 m telescope at Five College Radio Astronomy Observatory (FCRAO). We confirm the results of Maddalena & Thaddeus (1985) that the cloud is unusually cold and has very broad line widths (Delta V approximately 8 km/s). The exceptionally low gas temperatures (less than 8 K) can be explained if the cosmic-ray heating rate is reduced by a factor of 2 in the outer Galaxy. The mass of the cloud has been established by several techniques, and masses between 1 x 105 and 6 x 105 solar mass were obtained. We suggest that G216-2.5 is a remnant cloud from a past episode of massive star formation, for the following reasons. First, the cloud has a relatively large velocity dispersion for a non-star-forming GMC. Second, there is a clear evidence for shells and rings within the cloud, which may be the fossil remains of its earlier star formation activity. Third, the kinematics of the cloud are dominated by a global velocity gradient, suggesting that the cloud is part of a very large expanding shell. Finally, the discrepancy between the local thermodynamic equilibrium (LTE) and virial masses may be explained if the cloud has been severely perturbed and is currently expanding. G216-2.5 may be part of a larger star-forming complex that includes the adjacent H II region S287 and its molecular cloud.

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