The stellar distribution function and local vertical potential from Gaia DR2
Abstract
We develop a novel method to simultaneously determine the vertical potential, force, and stellar z-vz phase space distribution function (DF) in our local patch of the Galaxy. We assume that the Solar Neighbourhood can be treated as a one-dimensional (1D) system in dynamical equilibrium and directly fit the number density in the z-vz plane to what we call the rational linear distribution function (RLDF) model. This model can be regarded as a continuous sum of isothermal DFs though it has only one more parameter than the isothermal model. We apply our method to a sample of giant stars from Gaia Data Release 2 and show that the RLDF provides an excellent fit to the data. The well-known phase space spiral emerges in the residual map of the z-vz plane. We use the best-fitting potential to plot the residuals in terms of the frequency and angle of vertical oscillations and show that the spiral maps into a straight line. From its slope, we estimate that the phase spirals were generated by a perturbation ∼540 Myr years ago. We also determine the differential surface density as a function of vertical velocity dispersion, a.k.a. the vertical temperature distribution. The result is qualitatively similar to what was previously found for SDSS/SEGUE G dwarfs. Finally, we address parameter degeneracies and the validity of the 1D approximation. Particularly, the mid-plane density derived from a cold sub-sample, where the 1D approximation is more secure, is closer to literature values than that derived from the sample as a whole.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- May 2021
- DOI:
- 10.1093/mnras/stab574
- arXiv:
- arXiv:2101.07080
- Bibcode:
- 2021MNRAS.503.1586L
- Keywords:
-
- Galaxy: disc;
- Galaxy: evolution;
- Galaxy: kinematics and dynamics;
- (Galaxy:) solar neighborhood;
- Galaxy: structure;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 15 pages, 16 figures