Self--gravity and Dissipation in Polar Rings

Details Self--gravity and Dissipation in Polar Rings Self--gravity and Dissipation in Polar Rings

Dec 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...183.4209d&link_type=abstract

American Astronomical Society, 183rd AAS Meeting, #42.09; Bulletin of the American Astronomical Society, Vol. 25, p.1355

Astronomy and Astrophysics

Astronomy

Scientific paper

Studies of inclined rings inside galaxy potentials have mostly considered the influence of self-gravity and viscous dissipation separately. In this study, we construct models of highly-inclined ("polar") rings in an external potential including both self-gravity and dissipation due to a drag force. We do not include pressure forces and thus ignore shock heating that dominates the evolution of gaseous rings inside strongly nonspherical potentials. We adopt an oblate spheroidal scale-free logarithmic potential with axis ratio q=0.85 and an initial inclination of 80(deg) for the self-gravitating rings. We find that stellar (dissipationless) rings suffer from mass loss during their evolution. Mass loss also drives a secular change of the mean inclination toward the poles of the potential. As much as half of the ring mass escapes in the process and forms an inner and an outer shell of precessing orbits. If the remaining mass is more than ~0.02 of the enclosed galaxy mass, rings remain bound and do not fall apart from differential precession. The rings precess at a constant rate for more than a precession period tau_p finding the configuration predicted by Sparke (1986) which warps at larger radii toward the poles of the potential. We model shear viscosity with a velocity-dependent drag force and find that nuclear inflow dominates over self-gravity if the characteristic viscous inflow time scale tau_vi is shorter than ~25 tau_p . Rings with tau_vi / tau_p sles 25 collapse toward the nucleus of the potential within one precession period independent of the amount of self-gravity. Our results imply that stars and gas in real polar rings exhibit markedly different dynamical evolutions. This work is supported in part by NASA grant NAGW-1510, NSF grant AST 91-48279, and by a CfA Postdoctoral fellowship.

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