A study of the evolution of bulges and disks of spiral galaxies in interacting and isolated environments

Abstract

Galaxies usually reside in groups and clusters where they interact gravitationally. These interactions affect the internal dynamics of the galaxies. In this thesis, we have studied the effect of flyby interactions and dark matter distributions on the evolution of bulges and disks of spiral galaxies. To understand the effect of flyby interactions on the bulges, disks, and spiral arms of Milky Way mass galaxies, we simulated disk galaxies with classical bulges and boxy/peanut pseudo-bulges, then performed their flyby interactions with 1/10 and 1/5 mass galaxies. Using photometric and kinematic bulge-disk decompositions of the major galaxy, we showed that the disks get shorter and thicker during flyby interactions. Classical bulges remain intact. However, pseudo-bulges become dynamically hotter. Tidally induced spiral arms are transient density waves. They form soon after pericenter passage and decay in two phases; the initial rapid winding and the subsequent slow winding. We showed that the spirals are the main drivers of wave-like vertical breathing motion seen in the Milky Way. Tidal interactions do not directly induce breathing motion. In another work, we showed that the oblate dark matter halos delay bar formation, so bar buckling is also delayed, but probate halos promote multiple bucklings. Due to multiple bucklings, boxy/peanut bulges in prolate halos show the maximum thickness. Using SDSS galaxies, we found that pseudo-bulges are diffuse compared to classical bulges and are commonly found in low mass galaxies. In the local volume, pseudo-bulges overcome the classical bulges even in bulge dominated galaxies, so more than $75\%$ of local volume is rotation dominated. Finally, we showed that bulgeless galaxies in Illustris TNG50 are metal-poor, have high specific angular momentum as compared to the galaxies with bulges and fall at the lower end of baryonic to dark matter mass ratio.