The Role of Secondary Bars in Bulge Formation

Summary

An analysis of stellar orbits in a doubly barred galaxy shows that the effect of a secondary bar is to destabilize the orbits, the process being accompanied by the appearance of vertical resonances which would enable stars to leave the galactic plane and move into the bulge. This phenomenon could contribute to bulge formation. Results of the orbital analysis are presented and their significance discussed.

Introduction

The role of a secondary bar in shaping the morphology of a galaxy and its possible contribution to bulge formation is an issue which is currently largely unexplored. With more powerful observing techniques beginning to become available, a new look at galaxies which had been classified as unbarred shows that several of them possess a primary bar and some even show secondary bars (Mulchaey et al. 1997). If secondary bars are more prevalent than previously supposed, it is conceivable that they play a role in the secular evolution of galaxies much in the same way as do central mass concentrations (e.g. Hasan & Norman 1990, Sellwood & Moore 1999, Merritt 1998.) Nested gaseous bars have been produced in N-body simulations (Friedli & Martinet 1993; Heller & Shlosman 1994) suggesting that a system of embedded bars may be effective in transporting gas to the galactic center (Pfenniger & Norman 1990, Shlosman et al. 1989), thus influencing galactic evolution. An intuitive insight into the evolutionary process may be gained by examining the stellar dynamics in such systems.