Using Gaia DR2 to Constrain Local Dark Matter Density and Thin Dark Disk

We use stellar kinematics from the latest Gaia data release (DR2) to measure the local dark matter density $\rho_{\rm DM}$ in a heliocentric cylinder of radius $R= 150 \ {\rm pc}$ and half-height $z= 200 \ {\rm pc}$. 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 dark matter self-interaction. Performing the statistical analysis within a Bayesian framework for three types of tracers, we obtain ${\rho_{\rm DM}= 0.016 \pm 0.010}$ M$_\odot$/pc$^3$ 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$_\odot$/pc$^2$ for scale heights below 100 pc with 95% confidence. 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 kinematic 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.