scholarly journals Signatures of the resonances of a large Galactic bar in local velocity space

2019 ◽  
Vol 626 ◽  
pp. A41 ◽  
Author(s):  
G. Monari ◽  
B. Famaey ◽  
A. Siebert ◽  
C. Wegg ◽  
O. Gerhard
Keyword(s):  
Distribution Function ◽  
Angular Momentum ◽  
Velocity Structure ◽  
Realistic Model ◽  
Velocity Space ◽  
Action Space ◽  
Space Distribution ◽  
Local Velocity ◽  
Phase Mixing ◽  
Spiral Arms

The second data release of the Gaia mission has revealed a very rich structure in local velocity space. In terms of in-plane motions, this rich structure is also seen as multiple ridges in the actions of the axisymmetric background potential of the Galaxy. These ridges are probably related to a combination of effects from ongoing phase-mixing and resonances from the spiral arms and the bar. We have recently developed a method for capturing the behaviour of the stellar phase-space distribution function at a resonance by re-expressing it in terms of a new set of canonical actions and angles variables valid in the resonant region. Here, by properly treating the distribution function at resonances, and by using a realistic model for a slowly rotating large Galactic bar with pattern speed Ωb = 39 km s−1 kpc−1, we show that no fewer than six ridges in local action space can be related to resonances with the bar. Two of these ridges at low angular momentum correspond to the corotation resonance, and can be associated with the Hercules moving group in local velocity space. Another ridge at high angular momentum corresponds to the outer Lindblad resonance, and can tentatively be associated with the velocity structure seen as an arch at high azimuthal velocities in Gaia data. The other ridges are associated with the 3:1, 4:1, and 6:1 resonances. The last can be associated with the so-called “horn” of the local velocity distribution. While it is clear that effects from spiral arms and incomplete phase-mixing related to external perturbations also play a role in shaping the complex kinematics revealed by Gaia data, the present work demonstrates that, contrary to common misconceptions, the bar alone can create multiple prominent ridges in velocity and action space.

scholarly journals Galactic bar resonances inferred from kinematically hot stars in Gaia EDR3

2021 ◽  
Vol 508 (1) ◽  
pp. 728-736
Author(s):  
Daisuke Kawata ◽  
Junichi Baba ◽  
Jason A S Hunt ◽  
Ralph Schönrich ◽  
Ioana Ciucă ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Angular Momentum ◽  
Numerical Simulations ◽  
Momentum Distribution ◽  
Action Space ◽  
Space Distribution ◽  
Local Perturbation ◽  
Disc Galaxy ◽  
Hot Stars ◽  
Pattern Speeds

ABSTRACT Using a numerical simulation of an isolated barred disc galaxy, we first demonstrate that the resonances of the inner bar structure induce more prominent features in the action space distribution for the kinematically hotter stars, which are less sensitive to the local perturbation, such as the transient spiral arms. Then, we analyse the action distribution for the kinematically hotter stars selected from the Gaia EDR3 data as the stars with higher values of radial and vertical actions. We find several resonance features, including two new features, in the angular momentum distribution similar to what are seen in our numerical simulations. We show that the bar pattern speeds of about Ωbar ∼ 34 and 42 km s−1 kpc−1 explain all these features equally well. The resonance features we find correspond to the inner 4:1, co-rotation (CR), outer 4:1, outer Lindblad, and outer 4:3 (CR, outer 4:1, outer Lindblad, outer 4:3, and outer 1:1) resonances, when Ωbar ∼ 34 (42) km s−1 kpc−1 is assumed.

scholarly journals Coma Berenices: The First Evidence for Incomplete Vertical Phase-mixing in Local Velocity Space with RAVE—Confirmed withGaiaDR2

2018 ◽  
Vol 2 (2) ◽  
pp. 32 ◽  
Author(s):  
G. Monari ◽  
B. Famaey ◽  
I. Minchev ◽  
T. Antoja ◽  
O. Bienaymé ◽  
...  
Keyword(s):  
Velocity Space ◽  
Local Velocity ◽  
Phase Mixing

Orbit Tomography of energetic particle distribution functions

2021 ◽  
Author(s):  
Luke Stagner ◽  
William W Heidbrink ◽  
Mirko Salewski ◽  
Asger Schou Jacobsen ◽  
Benedikt Geiger
Keyword(s):  
Distribution Function ◽  
Phase Space ◽  
Energetic Particle ◽  
Particle Distribution ◽  
Distribution Functions ◽  
Velocity Space ◽  
Space Distribution ◽  
Weight Functions ◽  
Ion Distribution ◽  
Fast Ions

Abstract Both fast ions and runaway electrons are described by distribution functions, the understanding of which are of critical importance for the success of future fusion devices such as ITER. Typically, energetic particle diagnostics are only sensitive to a limited subsection of the energetic particle phase-space which is often insufficient for model validation. However, previous publications show that multiple measurements of a single spatially localized volume can be used to reconstruct a distribution function of the energetic particle velocity-space by using the diagnostics' velocity-space weight functions, i.e. Velocity-space Tomography. In this work we use the recently formulated orbit weight functions to remove the restriction of spatially localized measurements and present Orbit Tomography, which is used to reconstruct the 3D phase-space distribution of all energetic particle orbits in the plasma. Through a transformation of the orbit distribution, the full energetic particle distribution function can be determined in the standard {energy,pitch,r,z}-space. We benchmark the technique by reconstructing the fast-ion distribution function of an MHD-quiescent DIII-D discharge using synthetic and experimental FIDA measurements. We also use the method to study the redistribution of fast ions during a sawtooth crash at ASDEX Upgrade using FIDA measurements. Finally, a comparison between the Orbit Tomography and Velocity-space Tomography is shown.

Distribution functions for resonantly trapped orbits in our Galaxy

2017 ◽  
Vol 13 (S334) ◽  
pp. 341-342
Author(s):  
G. Monari ◽  
B. Famaey ◽  
J.-B. Fouvry ◽  
J. Binney
Keyword(s):  
Distribution Function ◽  
Phase Space ◽  
Stellar Population ◽  
Distribution Functions ◽  
Space Distribution ◽  
Galactic Disc ◽  
Phase Mixing ◽  
Phase Space Distribution ◽  
Resonant Region ◽  
Time Average

AbstractWe show how to capture the behaviour of the phase-space distribution function (DF) of a Galactic disc stellar population at a resonance. This is done by averaging the Hamiltonian over fast angle variables and re-expressing the DF in terms of a new set of canonical actions and angles variables valid in the resonant region. We then assign to the resonant DF the time average along the orbits of the axisymmetric DF expressed in the new set of actions and angles. This boils down to phase-mixing the DF in terms of the new angles, such that the DF for trapped orbits only depends on the new set of actions. This opens the way to quantitatively fitting the effects of the bar and spirals to Gaia data in terms of distribution functions in action space.

Kinematical evolution of Globular Clusters

2019 ◽  
Vol 14 (S351) ◽  
pp. 524-527
Author(s):  
Maria A. Tiongco ◽  
Enrico Vesperini ◽  
Anna Lisa Varri
Keyword(s):  
Angular Momentum ◽  
Structural Properties ◽  
Globular Clusters ◽  
Velocity Dispersion ◽  
Three Dimensional ◽  
Stellar Populations ◽  
Velocity Space ◽  
Fundamental Understanding

AbstractWe present several results of the study of the evolution of globular clusters’ internal kinematics, as driven by two-body relaxation and the interplay between internal angular momentum and the external Galactic tidal field. Via a large suite of N-body simulations, we explored the three-dimensional velocity space of tidally perturbed clusters, by characterizing their degree of velocity dispersion anisotropy and their rotational properties. These studies have shown that a cluster’s kinematical properties contain distinct imprints of the cluster’s initial structural properties, dynamical history, and tidal environment. Building on this fundamental understanding, we then studied the dynamics of multiple stellar populations in globular clusters, with attention to the largely unexplored role of angular momentum.

scholarly journals Radial migration in a stellar galactic disc with thick components

2018 ◽  
Vol 616 ◽  
pp. A86 ◽  
Author(s):  
A. Halle ◽  
P. Di Matteo ◽  
M. Haywood ◽  
F. Combes
Keyword(s):  
Angular Momentum ◽  
Gravitational Potential ◽  
Effective Potential ◽  
Constant Speed ◽  
Galactic Disc ◽  
Spiral Arms ◽  
Radial Migration ◽  
Stellar Disc ◽  
Local Maxima ◽  
Corotation Radius

We study how radial migration affects the stars of a galaxy with a thin stellar disc and thicker stellar components. The simulated galaxy has a strong bar and lasting spiral arms. We find that the amplitude of the churning (change in angular momentum) is similar for thin and thick components, and of limited amplitude, and that stars of all components can be trapped at the corotation of the bar. With the exception of those stars trapped at the corotation, we find that stars far from their initial guiding radius are more likely to be so due to blurring rather than churning effects. We compare the simulation to orbits integration with a fixed gravitational potential rotating at a constant speed. In the latter case, stars trapped at corotation are churned periodically outside and inside the corotation radius, with a zero net average. However, as the bar speed of the simulated galaxy decreases and its corotation radius increases, stars trapped at corotation for several Gyrs can be churned on average outwards. In this work we have studied the location of extreme migrators (stars experimenting the largest churning) and find that extreme migrators come from regions on the leading side of the effective potential local maxima.

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