The disc origin of the Milky Way bulge: Dissecting the
  chemo-morphological relations using N-body simulations and APOGEE
  There is a long-standing debate on the origin of the metal-poor stellar
populations of the Milky Way (MW) bulge, with the two leading scenarios being
that these populations are either i) part of a classical metal-poor spheroid or
ii) the same population as the chemically defined thick disc seen at the Solar
neighbourhood. Here we test whether the latter scenario can reproduce the
observed chemical properties of the MW bulge. To do so we compare an N-body
simulation of a composite (thin+thick) stellar disc -- which evolves secularly
to form a bar and a boxy/peanut (b/p) bulge -- to data from APOGEE DR13. This
model, in which the thick disc is massive and centrally concentrated, can
reproduce the morphology of the metal-rich and metal-poor stellar populations
in the bulge, as well as the mean metallicity and [$\alpha$/Fe] maps as
obtained from the APOGEE data. It also reproduces the trends, in both longitude
and latitude, of the bulge metallicity distribution function (MDF).
Additionally, we show that the model predicts small but measurable azimuthal
metallicity variations in the inner disc due to the differential mapping of the
thin and thick disc in the bar. We therefore see that the chemo-morphological
relations of stellar populations in the MW bulge are naturally reproduced by
mapping the thin and thick discs of the inner MW into a b/p.
