Chaotic Propellers of Barred Galaxies and Central Explosions

The central theme of this thesis work is to explore the possibilities of spiral arm formations from instabilities formed inside the central region of disc galaxies. These instabilities originate from the central baryonic feedback and have many prospects regarding the evolution of disc galaxies. They can trigger the gravitational collapse inside the dense molecular clouds that lead to the formation of stars under suitable astrophysical circumstances. In the present work, the role of parameters like the molecular cloud's magnetic field, rotation, etc., has been investigated behind this explosion-triggered star formation process with the help of Jeans instability analysis. From this study, our essential observation is that the formation of star clusters is favoured by a strong magnetic field ($\sim 10 \; \mu$G), and the effect is enhanced at a more considerable distance from the centre. Again, this instability also contributes to the formation of stellar bars. This dense rotating component may drive out the chaotic stellar orbits from the disc through its two ends like a propeller. This process has been modelled in the thesis work from the viewpoint of chaotic scattering in open Hamiltonian systems. This analysis concludes that this bar-driven chaotic motion (or simply escaping motion) may lead to the forming of spiral arms or inner disc rings, depending on the bar strength. Our study also found that, compared to NFW dark haloes, the oblate dark haloes offer a more cohesive evolutionary framework for generating bar-driven escape structures in giant spiral and dwarf galaxies. Moreover, the formation of spiral arms via bar-driven escaping motion is only encouraged in galaxies with NFW dark haloes if they have highly energetic centres, like active galaxies.
Comment: PhD Thesis; 147 pages, 40 figures, 16 tables, comments are welcome