Box- and Peanut-Shaped Bulges

Abstract

Box- and peanut-shaped (b/p) bulges are not really that peculiar as it seemed in the past and very common processes are required to explain the high frequency. At present several mechanisms for their origin are discussed. These structures may result from material accreted from infalling satellite companions (soft merging) (Binney and Petrou, 1985; Whitmore and Bell, 1988). An alternative mechanism for forming b/p bulges are instabilities or resonances animated by bars (Combes et al., 1990; Raha et al., 1991). N-body simulations for stars in barred potentials have demonstrated that with regard to the shape of bulges this theory and observational evidence are consistent (Kuijken and Merrifield, 1995). Within this framework, however, the question what may cause the bar becomes even more important.