Abstract Details
| Name: Chanda Jog Affiliation: IISc, Bengaluru Conference ID: ASI2019_300 Title : Role of interstellar gas in supporting spiral structure in galaxies Authors and Co-Authors : Chanda J. Jog (Author- invited speaker); Soumavo Ghosh (Co-author) Abstract Type : Invited Abstract Category : Plenary Abstract : Galaxies commonly exhibit a two-armed global spiral structure which is largely understood in terms of the standard density wave theory. However, such a density wave would be destroyed by group transport within about a billion years, as shown in a classic paper by Toomre. In order to address this, we include the low-velocity dispersion component, namely interstellar gas, along with stars in the formulation of the density wave theory, and obtain the dispersion relation for this coupled system. We show that the inclusion of gas makes the group transport slower, thus allowing the spiral pattern to persist longer – for several billion years. Further, we show that the inclusion of gas is essential to get a stable density wave for the observed values of pattern speeds for four galaxies: NGC 6946, NGC 2997, M 51 and the Milky Way. Thus, even though gas contains a small mass fraction (about 15 %) of the galactic disk, it has a significant dynamical effect on the value of pattern speed allowed, and hence on the secular evolution of the galactic disc. |