Non-equilibrium in the Solar Neighbourhood using dynamical modelling with Gaia DR2

Abstract

Matter distribution models of the Milky Way galaxy are usually stationary, although there are known to be wave-like perturbations in the disc at $\sim 10\%$ level of the total density. Modelling of the overall acceleration field by allowing non-equilibrium is a complicated task. We must learn to distinguish whether density enhancements are persistent or not by their nature. In the present paper, we elaborate our orbital arc method to include the effects of massless perturbations and non-stationarities in the modelling. The method is tested by modelling of simulation data and shown to be valid. We apply the method to the Gaia DR 2 data within a region of $\sim 0.5$ kpc from the Sun and confirm that acceleration field in the Solar Neighbourhood has a perturbed nature -- the phase space density along the orbits of stars grow in the order of $h\lesssim 5\%$ per Myr due to non-stationarity. This result is a temporally local value and can be used only within the timeframe of a few Myrs. An attempt to pinpoint the origin of the perturbation shows that the stars having larger absolute angular momentum are the main carriers of the local perturbation. As they are faster than the average thin disc star, they are either originating further away and are close in their pericentre or they are perturbed locally by a fast co-moving perturber, such as gas disc inhomogenities.

16 pages, 13 figures, resubmitted after addressing the referees comments

References in corpus (10)

• The Gaia mission
• Tracing Galaxy Formation with Stellar Halos II: Relating Substructure in Phase- and Abundance-Space to Accretion Histories
• The Structure of the Milky Way's Bar Outside the Bulge
• NMAGIC: Fast Parallel Implementation of a Chi-Squared-Made-to-Measure Algorithm for Modelling Observational Data
• The Next Generation Virgo cluster Survey. V. modelling the dynamics of M87 with the Made-to-Measure method
• Galactoseismology and the Local Density of Dark Matter
• Implications of a time-varying Galactic potential for determinations of the dynamical surface density
• The role of stochastic and smooth processes in regulating galaxy quenching
• Quantifying torque from the Milky Way bar using Gaia DR2
• Measuring the Sun's velocity using Gaia EDR3 observations of Stellar Streams

Cited by in corpus (1)

• A Bayesian estimation of the Milky Way's circular velocity curve using Gaia DR3