Rediscovering the disc origin of the Milky Way bulge

Abstract

AbstractWe explore morphological, kinematic and chemical trends of boxy/peanut (b/p) bulges of Milky Way (MW)-type galaxies, to better understand the formation history of the MW’s bulge. We show, using N-body simulations with both a kinematically cold and a kinematically hot disc, that colder populations develop a more prominent bar and X-shaped peanut as compared to their hotter counterpart. Colder discs also exhibit lower line-of-sight velocities (when viewed edge-on) at the edges of the b/p compared to hot discs, in agreement with what is seen for the MW bulge. Furthermore, we explore an N-body model which has three co-spatial discs with metallicities which correspond to the stellar populations of the inner Milky Way, where the α-enhanced thick disc populations are massive and centrally concentrated. The metallicity trends seen in observations of the Bulge can be reproduced in the model without the need of adding any additional components, which hints to the disc origin of the MW’s bulge.