James Q. Feng, C. F. Gallo
An accurate computational method is presented to determine the mass distribution in a rotating thin-disk galaxy from given rotation curve by applying Newtonian dynamics for an axisymmetrically rotating thin disk of finite size with or without a central spherical bulge. The governing integral equation for mass distribution, resulting from the balance between the Newtonian gravitational force and centrifugal force due to rotation at every point on the disk, is transformed via a boundary-element method into a linear algebra matrix equation that can be solved numerically for any given rotation curve. The mathematical formulation of the thin-disk model can easily be extended to including a central spherical bulge. To illustrate the effectiveness of this computational method, mass distributions in several mature spiral galaxies consistent with various types of measured rotation curves are determined without the need of fictitious rotation velocity outside the "cut-off" radius. When a central spherical bulge is present, the total galactic mass increases only slightly but the mass distribution in the galaxy is altered in such a way that the periphery mass density is reduced while more mass appears toward the galactic center. By extending the computational domain beyond the galactic edge, we can determine rotation velocity outside the cut-off radius which appears to continuously decrease and gradually approach the Keplerian rotation velocity out over twice the cut-off radius. In examining the circular orbit stability, the galaxies with flat or increasing rotation velocities with radius seem to be more stable than those with decreasing rotation velocities especially in the region near the galactic edge.
View original:
http://arxiv.org/abs/1212.5317
No comments:
Post a Comment