Observed Properties of Boxy/Peanut/Barlens Bulges

Abstract

We review the observed morphological, photometric, and kinematic properties of boxy/peanut (B/P) shape bulges. Nearly half of the bulges in the nearby edge-on galaxies have these characteristics, which fraction is similar to the observed bar fraction in Hubble types earlier than Scd. B/P bulges are generally detected in the edge-on view, but it has been recently demonstrated that barlenses, which are lens-like structures embedded in bars, are the more face-on counterparts of the B/P bulges. Multi-component structural decompositions have shown that B/P/barlens structures are likely to account for most of the bulge light, including the early-type discs harboring most of the bulge mass in galaxies. These structures appear in bright galaxies, in a mass range near to the Milky Way mass. Also the other properties of these bulges, including morphology (X-shaped), kinematics (cylindrical rotation), or stellar populations (old), are similar to those observed in the Milky Way. Cool central discs are often embedded in the B/P/barlens bulges. Barred galaxies contain also dynamically hot classical bulges, but it is not yet clear to what extent they are really dynamically distinct structure components, and to what extent stars wrapped into the central regions of the galaxies during the formation and evolution of bars. If most of the bulge mass in the Milky Way mass galaxies in the nearby universe indeed resides in the B/P-shape bulges, and not in the classical bulges, that idea needs to be integrated into the paradigm of galaxy formation.