Rotation in molecular clouds

Details Rotation in molecular clouds Rotation in molecular clouds

Jan 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999a%26as..134..241p&link_type=abstract

Astronomy and Astrophysics Supplement, v.134, p.241-254

Astronomy and Astrophysics

Astrophysics

24

Ism: Clouds, Ism: Kinematics And Dynamics, Ism: Molecules, Ism: Structure

Scientific paper

We have investigated a broad range of evidence concerning rotation in molecular clouds. As a consequence, we show that trends in specific angular momentum J/M and angular velocity Omega are inconsistent with certain models of isothermal, non-magnetic cloud rotation. Similarly, models of rotation which invoke turbulent vorticity may have only limited applicability to clumps and condensations. There is evidence to favour an important role for rotation in maintaining the stability of disks, larger cloud structures, and perhaps a large fraction of intermediate sized clouds, whilst rotation may also be implicated in maintaining observed departures from cloud sphericity. Although it is conceivable that magnetic braking is responsible for the radial decrement in specific angular momentum, it appears that observed gradients dln(J/M)/dln(R) are significantly shallower than is normally anticipated through this mechanism. The variation of angular momentum with cloud mass M (viz. J~ M(1.7) ) appears to be highly correlated, and is consistent with models of clump merging in isothermal rotating clouds. Similarly, the orientations of the angular velocity vectors for clumps and condensations appear broadly random, suggesting a turbulent origin for observed components of Omega or, alternatively, a process of randomisation through magnetic and/or dynamic clump interactions. By contrast, isolated clouds (and perhaps also disks) are shown to have angular velocity vectors oriented predominantly towards the north and south galactic poles; a distribution which would be anticipated were components of J to arise from galactic shear. We show, finally, that most of the cloud subgroups appear to follow similar functional trends in J, J/M, and Omega . Disks and rings, on the other hand, appear to depart from these variations to a significant degree; a difference which presumably derives from their distinct spatio-kinematic structures. Table~1 is only available at the CDS in electronic from via ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

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