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R.F. Coker (LANL), S.R. Stolovy (SIRTF/Caltech), M.H. Christopher, N.Z. Scoville (Caltech)
The ``circumnuclear disk'' (CND) is a dense, clumpy, asymmetric ring-like feature centered on Sgr A*, the putative black hole in the center of the Galaxy. The outer edge of the CND is not distinct but extends for more than 7 pc; the distinct inner edge, at a radius of ~q 1.5 pc, surrounds the ``mini-spiral'' of the HII region, Sgr A West. We present 3D hydrodynamical models of the formation of the CND from multiple self-gravitating infalling clouds. We assume the clouds are initially Bonner-Ebert spheres, in equilibrium with a hot confining inter-cloud medium. We include the gravitational potential due to the point-mass of Sgr A* as well as the extended mass distribution of the underlying stellar population. The sum of the point-mass potential and a flat (\rho \propto r-1.75) power-law for the stellar distribution results in a minimum in the Keplerian velocity at ~q 4 pc. Cloud-cloud collisions serve to circularize the clouds' orbits so that a significant fraction of the cloud gas ends up on orbits near this radius.
We find that a single cloud cannot reproduce the clumpy morphology of the CND. Rather, multiple clouds on diverse trajectories are required. Low density clumps are disrupted before reaching the inner CND radius, forming short-lived arcs. The outer parts of more massive clumps get tidally stripped, forming long-lived low-density arcs, while their cores undergo gravitational collapse. By collapsing quickly enough so that their core density exceeds the Roche limit at their final radius, clouds which initially exceed their Jeans mass can survive intact at small radii. Thus, we predict that clumps within the CND are sites of present or future star formation. However, in order for the CND to be a long-lived object, it must be continually fed by additional infalling clouds.
This work was supported in part by UK PPARC and DOE.
The author(s) of this abstract have provided an email address for comments about the abstract: robc@lanl.gov
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.