Astrolinguistics

Ollongren, Alexander

doi:10.1007/978-1-4614-5468-7

Cited by 15 publications

(1 citation statement)

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“…In fact, if two principal axis of the dispersion ellipsoid are aligned with the i-th and j-th axis, we have σ 2 ij =0, and the two velocity components are uncorrelated. The orientation of the dispersion ellipsoid of an old, dynamically relaxed population is related to the shape of the Galactic potential (Lynden-Bell 1962;Ollongren 1962;Hori & Liu 1963), and can indicate the presence of non-axisymmetric structures in the disk (Kuijken & Tremaine 1991). Moreover, Bienaymé (2009) and Siebert et al (2008) have shown that the vertical tilt of the ellipsoid allows to estimate the flattening of the dark halo.…”

Section: Orientation Of the Dispersion Ellipsoidmentioning

confidence: 99%

Kinematical and Chemical Vertical Structure of the Galactic Thick Disk. I. Thick Disk Kinematics,

Bidin

Carraro

Méndez

2012

ApJ

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The variation of the kinematical properties of the Galactic thick disk with Galactic height Z are 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 LSR alone cannot explain these observations. The rotational velocity decreases with |Z| by −30 km s −1 kpc −1 , but the data are better represented by a power-law with index 1.25, similar to that proposed from the analysis of SDSS 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 σ U /σ W =2 suggests that the thick disk could have formed from a low-latitude merging event. The vertex deviation increases with Galactic height, reaching ∼20 degrees 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 MOND, 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.

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