Abstract Details
| Name: Soumavo Ghosh Affiliation: IUCAA, Pune Conference ID: ASI2019_184 Title : Dynamical Imprint of Dark Matter Halo and Interstellar Gas on Spiral Structure in Disk Galaxies Authors and Co-Authors : Soumavo Ghosh; Chanda J. Jog & Tarun Deep Saini (PhD supervisors) Abstract Type : Oral Abstract Category : Thesis Abstract : Spiral arms play a pivotal role in secular evolution and shaping up the chemo-dynamical structure in disk galaxies - this is well-known. Spiral arms scatter stars off the disk mid-plane resulting in heating up the disk, participate in transferring angular momentum from one region to another facilitating the gas inflow in the central regions and influencing the central star formation activity, and also make the stars to migrate from their birth-place. In this doctoral thesis, I have investigated the impact of two structural components, namely, the dark matter halo and the interstellar gas, on the origin and persistence issue of the spiral arms. These studies have been carried out under two well-known paradigms for generation of spiral arms, namely, the density wave theory and the swing amplification mechanism. 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. Based on the studies reported in this thesis, the dark matter halo and the interstellar gas are shown to have opposite dynamical effect on the origin and persistence of spiral structure in disk galaxies. Using observational inputs for a sample of dark matter dominated low-surface-brightness galaxies and dwarf irregular galaxies with extended HI disks, I showed that dominant dark matter halo suppresses both the small-scale and large-scale spiral instabilities in disk galaxies. On the other hand, the interstellar gas is shown to decrease the group velocity of a wavepacket of density wave in Milky Way-like galaxies and thus help the spiral features to survive for a longer time-scale (several billion years). Also, using observed rotation curves and measured pattern speeds of spiral arm for three gas-rich disk galaxies, I showed that the interstellar gas is necessary for getting a stable density wave for observed pattern speed. |