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Astron. Astrophys. 327, 325-332

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Physical properties of molecular clouds
in the southern outer Galaxy

J. May, H. Alvarez, and L. Bronfman

Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile

Received 30 January 1996 / Accepted 2 April 1997


We have used a deep CO survey of the third galactic quadrant (May et al. 1993) to derive the physical properties of molecular clouds in the outer Galaxy. Within the range of this survey, from 194FORMULA to 270FORMULA in galactic longitude, 177 molecular clouds have been identified beyond 2 kpc from the Sun. Distances have been determined kinematically using the rotation curve of Brand (1986) with FORMULA kpc and FORMULA km s-1.

Power-law relations between line widths and sizes of the clouds, and between their densities and sizes have been found, although they do not fulfill exactly the requirements to be in virial equilibrium. Adopting a CO luminosity-to-H2 conversion factor X = 3.8 1020 molecules cm-2 (K km s-1)-1, the derived MCO masses statistically agree with the virial masses. The derived size and mass distributions show that the clouds are smaller, less massive and with narrower lines than those in the inner Galaxy. However, the mass spectrum for the clouds in our sample with masses FORMULA has a slope -1.45 which is similar to that found for inner Galaxy clouds.

The warping and flaring of the outer molecular disk is clearly delineated.

Key words: ISM: clouds - ISM: molecules - galaxy: general - radio lines: ISM

Send offprint requests to: J. May

© European Southern Observatory (ESO) 1997

Online publication: October 1, 1997
Last change: April 8, 1998