Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002arep...46..721b&link_type=abstract
Astronomy Reports, Vol. 46, Issue 9, pp. 721-730
Astronomy and Astrophysics
Astronomy
2
Scientific paper
We explore the hypothesis that the outer boundaries (“cutoffs”) of the stellar disks observed in many galaxies are determined by the condition of local gravitational (Jeans) stability for the gaseous protodisks at large galactocentric distances. The ratio of the surface density of the disk Σdisk to the critical value for Jeans instability Σcrit is computed for a number of galaxies, assuming that the gas velocity dispersion in the forming disk corresponded to its current thickness and that the disk itself is in a quasi-equilibrium state. The mean estimated stellar velocity dispersion in the vicinity of the cutoff (12 km/s) is close to the typical velocity dispersions of gaseous clouds in disk galaxies. At greater distances, such velocity dispersions should ensure gravitational stability of the disk both at the present epoch and in the past. The cutoff radius of the disk R cut is correlated with other disk parameters, and the ratio Σdisk/Σcrit at R cut is close to unity in most cases. We conclude that the available observational data agree well with the hypothesis that stellar disk cutoffs are due to a rapid decrease in the star-formation rate beyond R cut, where the gaseous disk has always been stable.
Bizyaev D. V.
Zasov Anatoli V.
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