Dynamical Imprint of Dark Matter Halo and Interstellar Gas on Spiral
  Structure in Disk Galaxies
  This thesis investigates the dynamical effect of two structural components of
disk galaxies, namely, the dark matter halo and the interstellar gas on the
origin and persistence issue of spiral structure in disk galaxies through
theoretical modeling and numerical calculations. These studies have been
carried out under two well-known paradigm for generation of spiral arms,
namely, the density wave theory and the small-scale material arm generated by
swing amplification. The basic theoretical model of the galactic disk used
involves gravitationally-coupled two-component system (stars and gas) embedded
in a rigid and non-responsive dark matter halo. The first part of the thesis
involves searching for the dynamical effect of dark matter halo on small-scale
spiral structure in dwarf low surface brightness (LSB) galaxies and also some
dwarf irregular galaxies which host an extended HI disk. In both cases, the
rotation curves are found to be dominated by the contribution of the dark
matter halo over a large radial distance, starting from the inner regions of
the galaxies. The next part of the thesis deals with the investigation of the
possible effect of the interstellar gas on the persistence issue and the
pattern speeds of the spiral structure in the disk galaxies. The last part of
the thesis involves in studying the dynamical effect of dark matter halo on
large-scale spiral structure. As shown in this thesis, the dark matter halo and
the interstellar have opposite dynamical effects on the origin and persistence
issue of the spiral arms. The dark matter halo suppresses both small-scale and
large-scale spiral instability in those disk galaxies which are dynamically
dominated by dark matter halo from the very innermost regions. On the other
hand, the interstellar gas helps the spiral arms to survive for a longer
time-scale (several billion year).
