The Bulge Radial Velocity/Abundance Assay

Details The Bulge Radial Velocity/Abundance Assay The Bulge Radial Velocity/Abundance Assay

2011-08-30

arxiv.org/abs/1108.6044v1

Astronomy and Astrophysics

Astrophysics

Galaxy Astrophysics

To appear in the Carnegie Observatories Astrophysics Series, volume 5

Scientific paper

The Bulge Radial Velocity/Abundance Assay (BRAVA) has accomplished a survey of 10,000 red giants in the Southern Galactic bulge, approximately spanning -8 deg. < l < +8 deg. and -3 deg. 90% of the bulge population is in the bar, leaving little room for a "classical" bulge component. We also report on the first iron abundance and composition measurements in the outer bulge, at b=-8 deg. The iron abundance in this field falls on the trend of a suspected gradient measured from high resolution spectroscopy of bulge clump stars. Further, we find that the trends of [\alpha/Fe] vs [Fe/H] that characterize the bulge at lower latitude are present 1 kpc from the nucleus, consistent with a rapid (<1 Gyr) timescale for the formation of the bulge, even near its boundary. Although the dynamics of the bulge are consistent with those of a dynamically buckled N-body bar, the presence of an abundance gradient is not compatible with purely dynamical processes; we propose that missing baryonic physics is needed. We also report on the remarkable massive bulge globular cluster Terzan 5, which has a bimodal abundance and composition distribution, and is proposed as the remnant of a population of primordial building block stellar systems that formed the bulge. Terzan 5 is presently a unique case, and it is important to test whether the dissolution of systems similar to it populated the bulge.