Implications of a time-varying Galactic potential for determinations of the dynamical surface density

Abstract

Recent studies have shown that the passage of a massive satellite through the disk of a spiral galaxy can induce vertical wobbles in the disk and produce features such as in-plane rings and phase-space spirals. Here we analyze a high-resolution N-body simulation of a live stellar disk perturbed by the recent passage of a massive dwarf galaxy that induces such perturbations. We study the implications of the phase-space structures for the estimate of the matter density through traditional Jeans modelling. The dwarf satellite excites rapid time-variations in the potential, leading to a significant bias of the local matter surface density determined through such a method. In particular, while the Jeans modelling gives reasonable estimates in the most overdense regions of the disk, we show that it tends to overestimate the dynamical surface density in underdense regions. In these regions, the phase-space spiral is indeed more marked in the surface of section of height vs. vertical velocity. This prediction can be verified with future Gaia data releases. Our finding is highly relevant for future attempts at determining the dynamical surface density of the outer Milky Way disk as a function of radius. The outer disk of the Milky Way is indeed heavily perturbed, and \textit{Gaia} DR2 data have clearly shown that such phase-space perturbations are even present locally. While our results show that traditional Jeans modelling should give reliable results in overdense regions of the disk, the important biases in underdense regions call for the development of non-equilibrium methods to estimate the dynamical matter density locally and in the outer disk.

Accepted for publication in ApJL

References in corpus (12)

• On the local dark matter density
• Rings and Radial Waves in the Disk of the Milky Way
• A new determination of the local dark matter density from the kinematics of K dwarfs
• Cold Dark Matter Substructure and Galactic Disks II: Dynamical Effects of Hierarchical Satellite Accretion
• Is the Milky Way ringing? The hunt for high velocity streams
• Bending and Breathing Modes of the Galactic Disk
• Radial and vertical flows induced by galactic spiral arms: likely contributors to our "wobbly Galaxy''
• Weighing the local dark matter with RAVE red clump stars
• Tracing the Hercules stream with Gaia and LAMOST: new evidence for a fast bar in the Milky Way
• The Vertical Structure and Kinematics of Grand Design Spirals
• Galactoseismology and the Local Density of Dark Matter
• Ripple patterns in in-plane velocities of OB stars from LAMOST and Gaia

Cited by in corpus (15)

• Hic sunt dracones: Cartography of the Milky Way spiral arms and bar resonances with Gaia Data Release 2
• Measuring the local dark matter density with LAMOST DR5 and Gaia DR2
• The phase spiral in Gaia DR3
• Gaia-DR2 extended kinematical maps. Part II: Dynamics in the Galactic disk explaining radial and vertical velocities
• Eclipse timing the Milky Way's gravitational potential
• Weighing the Galactic disk using phase-space spirals III. Probing distant regions of the disk using the Gaia EDR3 proper motion sample
• Weighing the Galactic disk in sub-regions of the solar neighbourhood using Gaia DR2
• Estimating the local dark matter density in a non-axisymmetric wobbling disc
• The North/South Asymmetry of the Galaxy: Possible Connection to the Vertical Phase Space Snail
• Ripples spreading across the Galactic disc. Interplay of direct and indirect effects of the Sagittarius dwarf impact
• On the Galactic rotation curve inferred from the Jeans equations Assessing its robustness using Gaia DR3 and cosmological simulations
• A Pulsar-Based Map of Galactic Acceleration
• Non-equilibrium in the Solar Neighbourhood using dynamical modelling with Gaia DR2
• The imprint of dark matter on the Galactic acceleration field
• Exploring the centre of mass properties of LG-like galaxies