Phylogeny of the Milky Way's inner disk and bulge populations:
  Implications for gas accretion, (the lack of) inside-out thick disk
  formation, and quenching
  We show that the bulge and the disk of the Milky Way (MW) at R$\lesssim$7~kpc
are well described by a unique chemical evolution and a two-phase
star-formation history (SFH). We argue that the populations within this inner
disk, not the entire disk, are the same, and that the outer Lindblad resonance
(OLR) of the bar plays a key role in explaining this uniformity. In our model
of a two-phase star formation history, the metallicity, [$\alpha$/Fe] and
[$\alpha$/H] distributions, and age-metallicity relation are all compatible
with the observations of both the inner disk and bulge. The dip at
[Fe/H]$\sim$0 dex seen in the metallicity distributions of the bulge and inner
disk reflects the quenching episode in the SFH of the inner MW at age $\sim$8
Gyr, and the common evolution of the bulge and inner disk stars. We show that
at z$\le$1.5, when the MW was starting to quench, transitioning between the end
of the $\alpha$-enhanced thick disk formation to the start of the thin disk,
and yet was still gas rich, the gas accretion rate could not have been
significant. The [$\alpha$/Fe] abundance ratio before and after this quenching
phase would be different, which is not observed. The present analysis suggests
that Milky Way history, and in particular at the transition from the thick to
the thin disk -- the epoch of the quenching -- must have been driven by a
decrease of the star formation efficiency. We argue that the decline in the
intensity of gas accretion, the formation of the bar, and the quenching of the
SFR at the same epoch may be causally connected thus explaining their temporal
coincidence (abridged).
