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The Bulge Radial Velocity Assay (BRAVA): I. Sample selection and a rotation curve

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  • Christian D. Howard
  • R. Michael Rich
  • David B. Reitzel
  • Andreas Koch
  • Roberto de Propris
  • HongSheng Zhao
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<mark>Journal publication date</mark>1/12/2008
<mark>Journal</mark>The Astrophysical Journal
Issue number2
Volume688
Number of pages18
Pages (from-to)1060-1077
Publication StatusPublished
<mark>Original language</mark>English

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.