Using Gaia DR2 to constrain local dark matter density and thin dark disk

Abstract

We use stellar kinematics from the latest Gaia data release (DR2) to measure the local dark matter (DM) density ρ_DM in a heliocentric cylinder of radius R= 150 pc and half-height z= 200 pc. We also explore the prospect of using our analysis to estimate the DM density in local substructure by setting constraints on the surface density and scale height of a thin dark disk aligned with the baryonic disk and formed due to dissipative dark matter self-interactions. Performing the statistical analysis within a Bayesian framework for three types of tracers, we obtain ρ_DM = 0.016 ± 0.010 M_solar/pc³ for A stars; early G stars give a similar result, while F stars yield a significantly higher value. For a thin dark disk, A stars set the strongest constraint: excluding surface densities (5-12) M_solar/pc² for scale heights below 100 pc with 95% confidence. The upper bound of this constraint implies lsim 1% of the Milky Way DM mass is present in a dissipative dark sector. Comparing our results with those derived using Tycho-Gaia Astrometric Solution (TGAS) data, we find that the uncertainty in our measurements of the local DM content is dominated by systematic errors that arise from assumptions of our dynamical analysis in the low z region. Furthermore, there will only be a marginal reduction in these uncertainties with more data in the Gaia era. We comment on the robustness of our method and discuss potential improvements for future work.