Dr. Sandeep Kataria

In this seminar, I will be presenting the work conducted as a part of my PhD thesis. In the first part, we have used two types of N-body galaxy models, one with dense bulges and another with rare bulges, in order to see the effect of both bulge mass and bulge concentration on bar formation. We derive a generalized criterion for bar formation which states that if the ratio of the radial force due to the bulge component and the radial force due to the total galaxy exceeds a value of 0.35, the galactic disk is stable against bar instability. We also performed an observational study to test the applicability of this criterion. We find that most of the galaxies agree with our criterion with only a few outliers. In the second part, we have also looked at the effect of bulge mass on the pattern speeds of disk galaxies with the motivation being to understand the origin of slow and fast bars along the Hubble sequence. We find that there are two important factors; 1) the rate of slow down of bar rotation increases with bulge mass and 2) bar formation time scales are delayed when bulge mass increases. We discuss the physical processes that lead to these effects. Finally, we have also examined whether bars in galaxies can provide insights into the core-cusp problem of LCDM cosmology. We show that as a bar rotates in the disk, it transfers angular momentum from the disk to the dark matter halo component and as a result slows down. This transfer of angular momentum is sufficient to alter the dark matter profile which depends on the resolution of the simulations. We conclude that the time scale for cusp to core transition is too large in barred disk galaxies to be meaningful for resolving the core-cusp problem of LCDM cosmology