Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993mnras.263..875i&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Vol. 263, NO.4/AUG15, P. 875, 1993
Astronomy and Astrophysics
Astronomy
35
Celestial Mechanics, Stellar Dynamics - Solar System: Formation - Galaxy: Kinematics And Dynamics - Solar Neighbourhood
Scientific paper
The velocity dispersion of particles in a disc potential is anisotropic. N-body simulations and observations show that the ratio between the radial component of the dispersion, σR, and the vertical one, σZ, is σZ/σR ≃ 0.6 for stars in a galactic disc in the solar neighbourhood, and σZ/σR ≃ 0.5 for planetesimals in a Kepler potential. These ratios are smaller than the `isotropic' ratio, σZ/σR = 1.
The velocity dispersion evolves through gravitational scattering between particles. To explain the anisotropic ratio, we performed analytical calculations using the two- body approximation which is similar to that of Lacey, although we calculate the logarithmic term ln Λ in the two-body approximation more exactly, since we found that the equilibrium ratio of σZ/σR depends sensitively on the choice of ln Λ. We determined the effective ln Λ for each component of velocity distribution, while Lacey simply took ln Λ as a constant. The numerical results of orbital integrations show that our treatment is correct, whereas Lacey's overestimated dσ2Z/dt and underestimated dσ2R/dt considerably, so that he overestimated the equilibrium ratio of σZ/σR. We find that the ratio σZ/σR approaches a value that is determined mainly by κ/Ω (where κ and ω are the epicyclic frequency and the angular velocity of a local circular orbit). The equilibrium ratios are predicted to be about 0.5 for the Kepler potential (κ/Ω = 1) and about 0.6 for the galactic potential in the solar neighbourhood (κ/Ω ≃ 1.4). Therefore the analytical calculation here explains well the ratios σZ/σR found by N-body simulations and observations.
Ida Shigeru
Kokubo Eiichiro
Makino Junichiro
No associations
LandOfFree
The Origin of Anisotropic Velocity Dispersion of Particles in a Disc Potential does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The Origin of Anisotropic Velocity Dispersion of Particles in a Disc Potential, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Origin of Anisotropic Velocity Dispersion of Particles in a Disc Potential will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1494049