Fig. 4

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Various dynamical quantities of the loL stars (left column) and hiL stars (middle column) and subclump stars (right column) in a potential with a triaxial halo with a range of p and q as calculated by AGAMA for an integration time of 100 Gyr. The grey horizontal line at p = 1 serves to guide the eye and indicates axisymmetric potentials. The white dotted line indicates the Ωϕ : Ωz = 1:1 resonance (see also bottom row). Top row: average Lyapunov exponent. A non-zero Lyapunov exponent indicates that there is chaoticity. The overlaid black contours, which are also shown in the other rows, map average(Λ*) at the levels of 0.02 and 0.04, as is also indicated on the colourbar. Second row: median variation in Lz, with ΔLz,* = max(Lz,*) − min(Lz,*) over the entire integration time. Third row: median variation in Ly, with ΔLy,* = max(Ly,*) − min(Ly,*) over the entire integration time. Bottom row: median(Ωϕ : Ωz) ratio. We can see clear correspondences between the four different rows. The chaotic regions overlap with the median(Ωϕ : Ωz) = 1:1 resonance and a transition in the value of ΔLz and ΔLy. This transition indicates a change in orbit family, and the text in the middle column indicates where the different orbit families reside, of which examples are shown in Fig. 5 (the crosses in this figure indicate their p and q). To the left of the chaotic band we find z-tube orbits, which have an oscillating Ly and a roughly conserved Lz, such that median(ΔLy) ≲ 4000 kpc km s−1, median(ΔLz) ≲ 500 kpc km s−1. To the right of the chaotic band we find y-tube orbits, which have a roughly conserved Ly and an oscillating Lz, such that median(ΔLy) ~ 1000 kpc km s−1 and median(Δ Lz) ~ 3000 kpc km s−1. For p > 1, the Ωϕ:Ωz = 1:1 is a resonance that traps orbits, which reduces their variation in both Ly and Lz. This is most clear for the subclump stars.
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