ARGOS III: Stellar Populations in the Galactic Bulge of the Milky Way
  We present the metallicity results from the ARGOS spectroscopic survey of the
Galactic bulge. Our aim is to understand the formation of the Galactic bulge:
did it form via mergers, as expected from Lambda CDM theory, or from disk
instabilities, as suggested by its boxy/peanut shape, or both? We have obtained
spectra for 28,000 stars at a spectral resolution of R = 11,000. From these
spectra, we have determined stellar parameters and distances to an accuracy of
< 1.5 kpc. The stars in the inner Galaxy span a large range in [Fe/H], -2.8 <
[Fe/H] < +0.6. From the spatial distribution of the red clump stars as a
function of [Fe/H] (Ness et al. 2012a), we propose that the stars with [Fe/H] >
-0.5 are part of the boxy/peanut bar/bulge. We associate the lower metallicity
stars ([Fe/H] < -0.5) with the thick disk, which may be puffed up in the inner
region, and with the inner regions of the metal-weak thick disk and inner halo.
For the bulge stars with [Fe/H] > -0.5, we find two discrete populations; (i)
stars with [Fe/H] ~ -0.25 which provide a roughly constant fraction of the
stars in the latitude interval b = -5 deg to -10 deg, and (ii) a kinematically
colder, more metal-rich population with mean [Fe/H] ~ +0.15 which is more
prominent closer to the plane. The changing ratio of these components with
latitude appears as a vertical abundance gradient of the bulge. We attribute
both of these bulge components to instability-driven bar/bulge formation from
the thin disk. We do not exclude a weak underlying classical merger-generated
bulge component, but see no obvious kinematic association of any of our bulge
stars with such a classical bulge component. [abridged]
