Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982japa....3..125a&link_type=abstract
Journal of Astrophysics and Astronomy, vol. 3, June 1982, p. 125-144.
Astronomy and Astrophysics
Astrophysics
4
Density Wave Model, Disk Galaxies, Galactic Bulge, Galactic Structure, Gravitational Effects, Spiral Galaxies, Gas Density, Gravitational Fields, Mass Ratios, Systems Stability
Scientific paper
The spiral arms of disk galaxies are very sensitive to various morphological properties, such as, the gas content, the disk-to-bulge ratio, etc. Here, the stability of self-gravitating annular disks surrounding the central rigid bulge component has been studied in order to explain the transition from the tight spiral arms in Sa galaxies to rather open patterns in Sc galaxies as the central amorphous component diminishes. Smooth spiral patterns are found associated with the dominant (or the fastest growing) modes of the system. When the disk-to-bulge mass ratio is small, a tight pattern results restricted to the inner regions of the disk. This pattern opens up and occupies larger disk areas as the disk component becomes comparable to the bulge. It is found here that the 'explosive' instabilities of the global density waves do not occur in the presence of a massive bulge. The growth-rates of the eigenmodes decrease as the disk-to-bulge mass ratio decreases. It is also found that unstable modes of the annular disk can be suppressed by increasing the thermal pressure sufficiently.
Ambastha Ashok
Varma Ram K.
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