IAU Symposium Abstract S186-052P

Formation of Boxy/Peanut-Shaped Bulges in Spiral Galaxies: Accretion or Bar-Instability?

M. Bureau1, and K. C. Freeman1
1 Mount Stromlo and Siding Spring Observatories,
The Australian National University, Australia
< martin@mso.anu.edu.au > < kcf@mso.anu.edu.au >

We present results of an observational program aimed at identifying the formation mechanism of boxy/peanut-shaped bulges in spiral galaxies. We concentrate on the accretion and bar-buckling scenarios and show that although satellites accretion is an attractive way to form boxy/peanut bulges, the bar-buckling instability is more likely to be the true cause of the bulges shape in the vast majority of cases. Nevertheless, some objects do not harbour a bar and others are clearly interacting, so the accretion mechanism could be relevant in some systems and the possibility of hybrid scenarios must be raised. The related X-shaped galaxies are also discussed.