Astron. Astrophys. 337, 105-112 (1998)

1. Introduction

Transport of angular momentum in the disks of spiral galaxies is one of the central issues in galactic dynamics. It is also of prime importance for fueling the central engines in active galactic nuclei (AGN). With regard to our own Galaxy this topic has been recently explored in a series of papers (von Linden et al. 1993a,b; Biermann et al. 1993) with the conclusion that the energy input from the SN explosions can feed the turbulence of the interstellar matter so as to provide the effective viscosity high as required to feed the star formation.

An immediate implication is that the viscous transport of angular momentum outwards is accompanied by inflow of gas inward with the rate that might be as high as  /yr on the scale of hundreds pc. Earlier, a similar mass inflow rate was inferred to exist on the scale of the circumnuclear disk, i.e. at 1.5 pc pc (Genzel & Townes 1987, Jackson et al. 1993).

We also note that the star formation in the inner region of the Galaxy requires such a mass supply.

However, appropriate physical mechanism(s) which would be able to provide the necessary rate of momentum transfer within the central 10 pc or so is (are) obscure so far. The present paper aims at consideration of such mechanisms. In Sect. 2 and Appendix, we discuss viscosity in a clumpy disk due to clump interactions, both with and without self-gravity included. Sect. 3 deals with short-wave instability of the clumpy, viscous disk; the necessary condition for developing small-scale turbulence is established here. In Sect. 4, we apply this mechanism to the circum-nuclear ring at the Galactic center. The results of the paper are discussed in Sect. 5.

© European Southern Observatory (ESO) 1998

Online publication: August 6, 1998
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