Mapping stellar kinematics across the Galactic bar: HST measurements of proper motions in 35 fields
Abstract
We present a proper motion mini-survey of 35 fields in the vicinity of Baade window, (l, b) = (1°, -4°), sampling roughly a 5 × 2.5-deg2 region of the Galactic bar. Our second epoch observations collected with the Advanced Camera for Surveys/High Resolution Channel instrument onboard the Hubble Space Telescope were combined with the archival Wide Field Planetary Camera 2/PC images. The resulting time baselines are in the range of 4 to 8 yr. Precise proper motions of 15863 stars were determined in the reference frame defined by the mean motion of stars with magnitudes between IF814W = 16.5 and 21.5 along the line of sight. We clearly detect small gradients in proper motion dispersions (σl, σb ~ (3.0, 2.5) mas yr-1, and in the amount of anisotropy (σl/σb ~ 1.2). Both the longitude dispersion σl and its ratio to the vertical motion σb increase towards the Galactic plane. The decline of the anisotropy ratio σl/σb towards the minor axis of the bulge is mostly due to increasing σb. We also find, for the first time, a significant negative covariance term in the transverse velocity field σlb/(σlσb) ~= -0.10. Our results extend by a factor of ~15 the number of the Galactic bar fields with good proper motion dispersions.
Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute (STScI). The STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. E-mail: simkoz@jb.man.ac.uk- Publication:
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Monthly Notices of the Royal Astronomical Society
- Pub Date:
- July 2006
- DOI:
- 10.1111/j.1365-2966.2006.10487.x
- arXiv:
- arXiv:astro-ph/0604550
- Bibcode:
- 2006MNRAS.370..435K
- Keywords:
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- gravitational lensing: Galaxy: bulge: Galaxy: disc: Galaxy: kinematics and dynamics;
- gravitational lensing;
- Galaxy: bulge;
- Galaxy: disc;
- Galaxy: kinematics and dynamics;
- Astrophysics
- E-Print:
- 11 pages, 7 figures, 3 tables, accepted for publication in MNRAS