||The Galactic Bulge
||491, Fifty Years of Wide Field Studies in the Southern Hemisphere: Resolved Stellar Populations in the Galactic Bulge and the Magellanic Clouds
||Rich, R. M.
||Observations at Cerro Tololo Inter-American Observatory (CTIO) have had a
critical formative impact on the study of the Galactic bulge, much of the
work being inspired and supported by Victor Blanco and collaborators, which
is presented in a historical overview. Recent observations at CTIO include
the Blanco 4m/Hydra Bulge Radial Velocity Assay (BRAVA) that has mapped the
Galactic bulge velocity field from –10<l <+10 and –10<b<–4. The velocity
field shows characteristic "cylindrical" rotation that is consistent with
the population being dominated by a kinematic bar that appears to have
originated from the secular evolution of a massive disk. Using the Hydra
multi-object spectrograph at CTIO, it has been shown that the bulge is dominated
by a population that is alpha enhanced relative to the thin and thick disk, and
shows the signature of the r-process being important in enrichment. Both
composition indicators are consistent with early, rapid formation of the bulge.
Although proper motion selected and field-subtracted color-magnitude diagrams
reaching the main sequence turnoff are consistent with the bulge being
globular cluster-age, analysis of microlensed dwarf stars favors a substantial
fraction of the bulge being younger than 5 Gyr. To help define the overall
picture of the bulge better, the Blanco DECam Bulge Survey (BDBS) will produce a
multicolor ugrizY map of the bulge from –10< l<+10 and –10<b<–2 that
will map the substructures as a function of metallicity and explore the spatial
distribution of stars as a function of age and metallicity.