The Bulge Radial Velocity Assay (BRAVA). I. Sample Selection and a Rotation Curve
Abstract
Results from the ongoing Bulge Radial Velocity Assay (BRAVA) are presented. BRAVA uses M red giant stars, selected from the 2MASS catalog to lie within a bound of reddening-corrected color and luminosity, as targets for the Cerro Tololo Inter-American Observatory 4 m Hydra multiobject spectrograph. Three years of observations investigate the kinematics of the Galactic bulge major (-10° < l < + 10°, b = - 4°) and minor (-6° < b < + 5°, -0.4° < l < 0.0°) axes with ~3300 radial velocities from 32 bulge fields and one disk field. We construct a longitude-velocity plot for the bulge stars and find that, contrary to previous studies, the bulge does not rotate as a solid body; from -4° < l < + 4° the rotation curve has a slope of roughly 100 km s-1 kpc-1 and flattens considerably at greater l, reaching a maximum rotation of 75 km s-1. We compare our rotation curve and velocity dispersion profile both to the self-consistent model of Zhao and to N-body models; neither fits both our observed rotation curve and velocity dispersion profile. We place the bulge on the plot of Vmax/σ vs. epsilon and find that the bulge lies near the oblate rotator line and very close to the parameters of NGC 4565, an edge-on spiral galaxy with a bulge similar to that of the Milky Way. We find that our summed velocity distribution of bulge stars appears to be sampled from a Gaussian distribution, with σ = 116 +/- 2 km s-1 for our full data set. Two candidate cold streams are not confirmed with additional data.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2008
- DOI:
- 10.1086/592106
- arXiv:
- arXiv:0807.3967
- Bibcode:
- 2008ApJ...688.1060H
- Keywords:
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- Galaxy: bulge;
- Galaxy: kinematics and dynamics;
- stars: kinematics;
- stars: late-type;
- techniques: radial velocities;
- Astrophysics
- E-Print:
- 45 pages, 21 figures, 4 tables. Accepted for publication in the Astrophysical Journal on 24 July 2008