KINEMATICAL AND CHEMICAL VERTICAL STRUCTURE OF THE GALACTIC THICK DISK. I. THICK DISK KINEMATICS ,
- Departamento de Astronomia, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile)
- European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago (Chile)
The variation of the kinematical properties of the Galactic thick disk with Galactic height Z is studied by means of 412 red giants observed in the direction of the south Galactic pole up to 4.5 kpc from the plane. We confirm the non-null mean radial motion toward the Galactic anticenter found by other authors, but we find that it changes sign at |Z| = 3 kpc, and the proposed inward motion of the local standard of rest alone cannot explain these observations. The rotational velocity decreases with |Z| by -30 km s{sup -1} kpc{sup -1}, but the data are better represented by a power law with index 1.25, similar to that proposed from the analysis of Sloan Digital Sky Survey data. All the velocity dispersions increase with |Z|, but the vertical gradients are small. The dispersions grow proportionally, with no significant variation of the anisotropy. The ratio {sigma}{sub U}/{sigma}{sub W} = 2 suggests that the thick disk could have formed from a low-latitude merging event. The vertex deviation increases with Galactic height, reaching {approx}20 Degree-Sign at |Z| = 3.5 kpc. The tilt angle also increases, and the orientation of the ellipsoid in the radial-vertical plane is constantly intermediate between the alignment with the cylindrical and the spherical coordinate systems. The tilt angle at |Z| = 2 kpc coincides with the expectations of MOdified Newtonian Dynamics, but an extension of the calculations to higher |Z| is required to perform a conclusive test. Finally, between 2.5 and 3.5 kpc we detect deviations from the linear trend of many kinematical quantities, suggesting that some kinematical substructure could be present.
- OSTI ID:
- 22016254
- Journal Information:
- Astrophysical Journal, Vol. 747, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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