On the vertical equilibrium of the local Galactic disk and the search for disk dark matter

TL;DR

This paper defends the assumption of vertical equilibrium in the Galactic disk, showing that previous doubts are unfounded and that steady-state models remain valid for estimating disk matter density.

Contribution

The study clarifies the energy ratio in disk models and demonstrates through simulations that the Galactic disk is likely in Virial equilibrium, supporting traditional measurement methods.

Findings

The energy ratio was overestimated in previous claims.

Numerical simulations confirm the disk is in Virial equilibrium.

Steady-state solutions remain valid for density estimates.

Abstract

Estimates of the dynamical surface mass density at the solar Galactocentric distance are commonly derived assuming that the disk is in vertical equilibrium with the Galactic potential. This assumption has recently been called into question, based on the claim that the ratio between the kinetic and the gravitational energy in such solutions is a factor of 3 larger than required if Virial equilibrium is to hold. Here we show that this ratio between energies was overerestimated and that the disk solutions are likely to be in Virial equilibrium after all. We additionally demonstrate, using one-dimensional numerical simulations, that the disks are indeed in equilibrium. Hence, given the uncertainties, we find no reason to cast doubt on the steady-state solutions which are traditionally used to measure the matter density of the disk.