Journal
ASTROPHYSICAL JOURNAL
Volume 728, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/728/1/7
Keywords
Galaxy: kinematics and dynamics; Galaxy: structure
Categories
Funding
- NSF [AST04-0908996, AST04-07292, AST04-07293]
- Anglo-Australian Observatory
- Astrophysical Institute Potsdam
- Australian National University
- Australian Research Council
- French National Research Agency
- German Research foundation
- Instituto Nazionale di Astrofisica di Padova
- Johns Hopkins University
- National Science Foundation of the USA [AST09-08326]
- W.M. Keck foundation
- Macquarie University
- Netherlands Research School for Astronomy
- Natural Sciences and Engineering Research Council of Canada
- Slovenian Research Agency
- Swiss National Science Foundation
- Science and Technology Facilities Council of the UK
- Opticon
- Strasbourg University
- Universities of Groningen, Heidelberg and Sidney
- NASA
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We analyze the three-dimensional kinematics of a sample of similar to 4400 red clump stars ranging between 5 and 10 kpc from the Galactic center and up to 3 kpc from the Galactic plane. This sample is representative for the metal-rich ([Fe/H] = -0.6 - +0.5) thick disk. Absolute proper motions are from the fourth release of the Southern Proper Motion Program and radial velocities from the second release of the Radial Velocity Experiment. The derived kinematical properties of the thick disk include the rotational velocity gradient partial derivative V-theta/partial derivative z = -25.2 +/- 2.1 km s(-1) kpc(-1), velocity dispersions (sigma(VR), sigma(V theta), sigma(Vz))vertical bar (z = 1) = (70.4, 48.0, 36.2)+/-(4.1, 8.3, 4.0) km s(-1), and velocity-ellipsoid tilt angle alpha(Rz) = 8.degrees 6 +/- 1.degrees 8. Our dynamical estimate of the thin-disk scale length is R-thin = 2.0 +/- 0.4 kpc and of the thick-disk scale height is z(thick) = 0.7 +/- 0.1 kpc. The observed orbital eccentricity distribution compared with those from four different models of the formation of the thick disk from Sales et al. favors the gas-rich merger model and the minor merger heating model. Interestingly, when referred to the currently accepted value of the LSR, stars more distant than 0.7 kpc from the Sun show a net average radial velocity of 13 +/- 3 km s(-1). This result is seen in previous kinematical studies using other tracers at distances larger than similar to 1 kpc. We suggest this motion reflects an inward perturbation of the locally defined LSR induced by the spiral density wave.
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