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

Abstract

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.

Conditions of consistency for multicomponent axisymmetric stellar systems

“…The non-vanishing tilt was also found by and Fuchs et al (2009). The general kinematic features of the thick disc are also in agreement with the results obtained by Carollo et al (2010), Pasetto et al (2012a), andMoni Bidin et al (2012), although the latter find a non-null vertex deviation of thick disc stars, which increases with the distance to the GC. It is worthwhile to remark that an axial symmetric model with a mean velocity non-symmetric about the plane z = 0 provides a vertex deviation proportional to z (Paper II, Appendix A).…”

The Galaxy in Context: Structural, Kinematic, and Integrated Properties

“…In addition to the warp, the outer disk flares in both stars and gas and possesses a fair degree of substructure. Moni Bidin, Carraro & Méndez (2012) review the contradicting claims for the flaring stellar disk, but the comprehensive study of Momany et al (2006) puts the issue beyond doubt. Carraro (2015) reviews the evidence for flaring in the outer disk in both young (HII regions, open clusters) and old stellar populations (cepheids, pulsars).…”

The Milky Way’s stellar disk

“…Kuijken and Gilmore (1989a), Nordström et al (2004), Fuhrmann (2011), Moni Bidin et al (2012. This then lessens, or even obviates the need to deal with the selection function explicitly in the subsequent astrophysical analysis.…”