Mapping stellar kinematics across the Galactic bar: HST measurements of proper motions in 35 fields

S. Kozlowski*, P. R. Wozniak, S. Mao, M. C. Smith, T. Sumi, W. T. Vestrand, L. Wyrzykowski

*Corresponding author for this work

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Abstract

We present a proper motion mini-survey of 35 fields in the vicinity of Baade window, (l, b) = (1 degrees, -4 degrees), sampling roughly a 5 x 2.5-deg(2) 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 15 863 stars were determined in the reference frame defined by the mean motion of stars with magnitudes between I(F814W) = 16.5 and 21.5 along the line of sight. We clearly detect small gradients in proper motion dispersions (sigma(l), sigma(b) similar to (3.0, 2.5) mas yr(-1), and in the amount of anisotropy (sigma(l)/sigma(b) similar to 1.2). Both the longitude dispersion sigma(l) and its ratio to the vertical motion sigma(b) increase towards the Galactic plane. The decline of the anisotropy ratio sigma(l)/sigma(b) towards the minor axis of the bulge is mostly due to increasing sigma(b). We also find, for the first time, a significant negative covariance term in the transverse velocity field sigma(lb)/(sigma(l)sigma(b)) similar or equal to -0.10. Our results extend by a factor of similar to 15 the number of the Galactic bar fields with good proper motion dispersions.

Original languageEnglish
Pages (from-to)435-443
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Volume370
Issue number1
DOIs
Publication statusPublished - 21-Jul-2006

Keywords

  • gravitational lensing
  • Galaxy : bulge
  • Galaxy : disc
  • Galaxy : kinematics and dynamics
  • GRAVITATIONAL LENSING EXPERIMENT
  • MICROLENSING OPTICAL DEPTH
  • DIFFERENCE IMAGE-ANALYSIS
  • BULGE FIELDS
  • PROJECT
  • SYSTEMS
  • GALAXY
  • MODEL

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