scholarly journals Quantifying torque from the Milky Way bar using Gaia DR2

2020 ◽  
Vol 494 (3) ◽  
pp. 3358-3367 ◽  
Author(s):  
Rain Kipper ◽  
Peeter Tenjes ◽  
Taavi Tuvikene ◽  
Punyakoti Ganeshaiah Veena ◽  
Elmo Tempel
Keyword(s):  
Phase Space ◽  
Milky Way ◽  
Space Distribution ◽  
Gravitational Acceleration ◽  
The Sun ◽  
Solar Mass ◽  
Stellar Orbits ◽  
Phase Space Distribution ◽  
Acceleration Field ◽  
Gaia Dr2

ABSTRACT We determine the mass of the Milky Way bar and the torque it causes, using Gaia DR2, by applying the orbital arc method. Based on this, we have found that the gravitational acceleration is not directed towards the centre of our Galaxy but a few degrees away from it. We propose that the tangential acceleration component is caused by the bar of the Galaxy. Calculations based on our model suggest that the torque experienced by the region around the Sun is $\approx 2400\, {\rm km^2\, s^{-2}}$ per solar mass. The mass estimate for the bar is $\sim 1.6\pm 0.3\times 10^{10}\, \mathrm{M_\odot }$. Using greatly improved data from Gaia DR2, we have computed the acceleration field to great accuracy by adapting the orbital Probability Density Function (oPDF) method (Han et al. 2016) locally and used the phase space coordinates of ∼4 × 105 stars within a distance of 0.5 kpc from the Sun. In the orbital arc method, the first step is to guess an acceleration field and then reconstruct the stellar orbits using this acceleration for all the stars within a specified region. Next, the stars are redistributed along orbits to check if the overall phase space distribution has changed. We repeat this process until we find an acceleration field that results in a new phase space distribution that is the same as the one that we started with; we have then recovered the true underlying acceleration.

scholarly journals Frequency maps as a probe of secular evolution in the Milky Way

2012 ◽  
Vol 10 (H16) ◽  
pp. 349-349
Author(s):  
Monica Valluri
Keyword(s):  
Dark Matter ◽  
Distribution Function ◽  
Phase Space ◽  
Milky Way ◽  
Space Distribution ◽  
Compact Representation ◽  
Phase Space Distribution ◽  
Secular Evolution ◽  
Halo Stars ◽  
Stellar Halo

AbstractThe frequency analysis of the orbits of halo stars and dark matter particles from a cosmological hydrodynamical simulation of a disk galaxy from the MUGS collaboration (Stinson et al. 2010) shows that even if the shape of the dark matter halo is nearly oblate, only about 50% of its orbits are on short-axis tubes, confirming a previous result: under baryonic condensation all orbit families can deform their shapes without changing orbital type (Valluri et al. 2010). Orbits of dark matter particles and halo stars are very similar reflecting their common accretion origin and the influence of baryons. Frequency maps provide a compact representation of the 6-D phase space distribution that also reveals the history of the halo (Valluri et al. 2012). The 6-D phase space coordinates for a large population of halo stars in the Milky Way that will be obtained from future surveys can be used to reconstruct the phase-space distribution function of the stellar halo. The similarity between the frequency maps of halo stars and dark matter particles (Fig. 1) implies that reconstruction of the stellar halo distribution function can reveal the phase space distribution of the unseen dark matter particles and provide evidence for secular evolution. MV is supported by NSF grant AST-0908346 and the Elizabeth Crosby grant.

scholarly journals Constraining the Milky Way Mass Profile with Phase-space Distribution of Satellite Galaxies

2020 ◽  
Vol 894 (1) ◽  
pp. 10 ◽  
Author(s):  
Zhao-Zhou Li ◽  
Yong-Zhong Qian ◽  
Jiaxin Han ◽  
Ting S. Li ◽  
Wenting Wang ◽  
...  
Keyword(s):  
Phase Space ◽  
Milky Way ◽  
Space Distribution ◽  
Phase Space Distribution ◽  
Mass Profile ◽  
Satellite Galaxies

scholarly journals On the ridges, undulations & streams in Gaia DR2: Linking the topography of phase-space to the orbital structure of an N-body bar

2019 ◽  
Author(s):  
F Fragkoudi ◽  
D Katz ◽  
W Trick ◽  
S D M White ◽  
P Di Matteo ◽  
...  
Keyword(s):  
Phase Space ◽  
Milky Way ◽  
The Sun ◽  
Orbital Structure ◽  
Thick Disc ◽  
Orbit Integration ◽  
Gaia Dr2 ◽  
Lindblad Resonance ◽  
Metallicity Distribution ◽  
Strong Asymmetry

Abstract We explore the origin of phase-space substructures revealed by the second Gaia data release in the disc of the Milky Way, such as the ridges in the Vφ-r plane, the undulations in the Vφ-r-Vr space and the streams in the Vφ-Vr plane. We use a collisionless N-body simulation with co-spatial thin and thick discs, along with orbit integration, to study the orbital structure close to the Outer Lindblad Resonance (OLR) of the bar. We find that a prominent, long-lived ridge is formed in the Vφ-r plane due to the OLR which translates to streams in the Vφ-Vr plane and examine which closed periodic and trapped librating orbits are responsible for these features. We find that orbits which carry out small librations around the x1(1) family are preferentially found at negative Vr, giving rise to a ‘horn’-like feature, while orbits with larger libration amplitudes, trapped around the x1(2) and x1(1) families, constitute the positive Vr substructure, i.e. the Hercules-like feature. This changing libration amplitude of orbits will translate to a changing ratio of thin/thick disc stars, which could have implications on the metallicity distribution in this plane. We find that a scenario in which the Sun is placed close to the OLR gives rise to a strong asymmetry in Vr in the Vφ-Vr plane (i.e. Hercules vs. ‘the horn’) and subsequently to undulations in the Vφ-r-Vr space. We also explore a scenario in which the Sun is placed closer to the bar corotation and find that the bar perturbation alone cannot give rise to the these features.

A one-dimensional self-gravitating stellar gas

1966 ◽  
Vol 25 ◽  
pp. 46-48 ◽  
Author(s):  
M. Lecar
Keyword(s):  
Gravitational Field ◽  
Phase Space ◽  
Motion Picture ◽  
Space Distribution ◽  
Two Dimensional ◽  
One Dimensional ◽  
Phase Space Distribution ◽  
Dimensional Phase Space ◽  
The Mean

“Dynamical mixing”, i.e. relaxation of a stellar phase space distribution through interaction with the mean gravitational field, is numerically investigated for a one-dimensional self-gravitating stellar gas. Qualitative results are presented in the form of a motion picture of the flow of phase points (representing homogeneous slabs of stars) in two-dimensional phase space.

Simulation study of Landau damping near the persisting to arrested transition

2017 ◽  
Vol 83 (4) ◽  
Author(s):  
Alexander J. Klimas ◽  
Adolfo F. Viñas ◽  
Jaime A. Araneda
Keyword(s):  
Phase Space ◽  
Simulation Study ◽  
High Speed ◽  
Space Distribution ◽  
Landau Damping ◽  
Field Mode ◽  
Low Speed ◽  
Phase Space Distribution ◽  
Saturation Stage ◽  
First Time

A one-dimensional electrostatic filtered Vlasov–Poisson simulation study is discussed. The transition from persisting to arrested Landau damping that is produced by increasing the strength of a sinusoidal perturbation on a background Vlasov–Poisson equilibrium is explored. Emphasis is placed on observed features of the electron phase-space distribution when the perturbation strength is near the transition value. A single ubiquitous waveform is found perturbing the space-averaged phase-space distribution at almost any time in all of the simulations; the sole exception is the saturation stage that can occur at the end of the arrested damping scenario. This waveform contains relatively strong, very narrow structures in velocity bracketing $\pm v_{\text{res}}$ – the velocities at which electrons must move to traverse the dominant field mode wavelength in one of its oscillation periods – and propagating with $\pm v_{\text{res}}$ respectively. Local streams of electrons are found in these structures crossing the resonant velocities from low speed to high speed during Landau damping and from high speed to low speed during Landau growth. At the arrest time, when the field strength is briefly constant, these streams vanish. It is conjectured that the expected transfer of energy between electrons and field during Landau growth or damping has been visualized for the first time. No evidence is found in the phase-space distribution to support recent well-established discoveries of a second-order phase transition in the electric field evolution. While trapping is known to play a role for larger perturbation strengths, it is shown that trapping plays no role at any time in any of the simulations near the transition perturbation strength.

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