The Bulge Radial Velocity Assay: A dynamical survey of the Milky Way bulge using evolved stars selected from the 2mum All Sky Survey

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Milky Way, Evolved Stars, Galactic Bulges, Radial Velocity

Scientific paper

This thesis presents results from the Bulge Radial Velocity Assay ( BRAVA ) , a dynamical survey of the Milky Way bulge. BRAVA uses M 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 multi-object spectrograph. Four years of observations investigate the kinematics of the Galactic bulge major and minor axes with (~4500 radial velocities from 43 bulge fields and one disk field. Using the techniques developed in this project, an additional 40 bulge fields, with ~4500 giants, have been observed.
We present our involvement with BRAVA, including the planning and execution of observations, sample selection, and data reduction techniques. We present longitude-velocity plots for two separate Galactic latitudes and find that, contrary to previous studies, the bulge does not rotate as a solid body; for | l | [Special characters omitted.] 4 degree the rotation curve has a slope of roughly 100 km s -1 kpc -1 and flattens considerably at greater 1, reaching a maximum rotation of 75 km s -1 . The study demonstrates (for the first time) cylindrical rotation of the bulge. This is a classic bar signature.
We compare the Galactic bulge rotation curve and velocity dispersion profile to both the self-consistent model of Zhao and to other N-body models; neither satisfactorily fits both measured rotation and dispersion. We place the bulge on the plot of (V max /s) vs. [straight 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 box-shaped bulge similar to that of the Milky Way. We find that our summed velocity distribution of bulge stars appears to be sampled from an approximately Gaussian distribution, with no obvious indication of disk and/or spheroidal contamination.

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