Astron. Astrophys. 327, 325-332 (1997)

Physical properties of molecular clouds in the southern outer Galaxy

J. May , H. Alvarez and L. Bronfman

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

Received 30 January 1996 / Accepted 2 April 1997

Abstract

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 to 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 kpc and .

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 molecules cm^-2 (K km s , the derived 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 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

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Contents

• 1. Introduction
• 2. Cloud properties
  • 2.1. Individual cloud properties
    • 2.1.1. Distance
    • 2.1.2. Radius
    • 2.1.3. Mass
  • 2.2. Statistical cloud properties
• 3. Distribution in the galactic disk
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: April 8, 1998
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