||The Transition between the Inner Disc and the Innermost Galactic Regions
||491, Fifty Years of Wide Field Studies in the Southern Hemisphere: Resolved Stellar Populations in the Galactic Bulge and the Magellanic Clouds
||Bono, G.; Genovali, K.; Lemasle, B.; Romaniello, M.; Nonino, M.; Bergemann, M.; Buonanno, R.; Fabrizio, M.; François, P.; Inno, L.; Laney, C.; Matsunaga, N.; Pedicelli, S.; Primas, F.; Thévenin, F.
||We discuss the iron and the α-element gradients in the Galactic
disc and in the innermost Galactic regions (bulge, bar, nuclear bulge).
Accurate spectroscopic measurements of young stellar tracers show a
well defined iron gradient between the inner and the outer disc.
The same outcome applies to light, α, and heavy elements.
Moreover, the [α/Fe] ratio attains solar values over a
significant fraction of the disc, in the bar and in the
nuclear bulge. Thus suggesting that the slopes
of iron and α–elements attain quite similar values.
There is evidence of a mild enhancement in the outer disc, but
this is the consequence of the steady decrease in iron abundance.
Current findings do not allow us to constrain whether the
chemical enrichment in the nuclear bulge and in the bar is
currently driven by bar instabilities.
The recent results by the ARGOS spectroscopic survey of intermediate-age stellar
tracers (red clump) suggest that the metal-rich stellar components
associated with the boxy/peanut bulge show evidence of a mild iron
gradient, while the metal-poor component associated with the thick
disc/halo shows a flat iron distribution across the bulge. The
[α/Fe] ratio of the metal-rich components is slightly
enhanced in the bulge, but attains a solar value in the disc.
On the other hand, the metal-poor component is α-enhanced
both in the bulge and at larger Galactocentric distances.
The chemical enrichment history of the bulge supports
N-body simulations suggesting that the bulge formed
via a bar-forming and bar-buckling instabilities
(Ness et al. 2013a,b).