# On the estimation of the Local Dark Matter Density using the rotation curve of the Milky Way

## TL;DR

This study assesses how different Galactic mass models influence the estimation of the local dark matter density using the Milky Way's rotation curve, highlighting the sensitivity to baryonic components and the limitations of the rotation curve method.

## Contribution

It systematically analyzes the impact of baryonic model choices on dark matter density estimates, emphasizing the potential for unaccounted thin components to significantly alter results.

## Key findings

- Estimated dark matter density is robust to halo model variations.
- Uncertainty in baryonic components, especially the disk, affects density estimates.
- Presence of a thin dark matter disk could increase density estimates by over a factor of 8.

## Abstract

The rotation curve of the Milky Way is commonly used to estimate the local dark matter density $\rho_{{\rm DM},\odot}$. However, the estimates are subject to the choice of the distribution of baryons needed in this type of studies. In this work we explore several Galactic mass models that differ in the distribution of baryons and dark matter, in order to determine $\rho_{{\rm DM},\odot}$. For this purpose we analyze the precise circular velocity curve measurement of the Milky Way up to $\sim 25$ kpc from the Galactic centre obtained from Gaia DR2 [1]. We find that the estimated value of $\rho_{{\rm DM},\odot}$ stays robust to reasonable changes in the spherical dark matter halo. However, we show that $\rho_{{\rm DM},\odot}$ is affected by the choice of the model for the underlying baryonic components. In particular, we find that $\rho_{{\rm DM},\odot}$ is mostly sensitive to uncertainties in the disk components of the Galaxy. We also show that, when choosing one particular baryonic model, the estimate of $\rho_{{\rm DM},\odot}$ has an uncertainty of only about $10\%$ of its best-fit value, but this uncertainty gets much bigger when we also consider the variation of the baryonic model. In particular, the rotation curve method does not allow to exclude the presence of an additional very thin component, that can increase $\rho_{{\rm DM},\odot}$ by more than a factor of 8 (the thin disk could even be made of dark matter). Therefore, we conclude that exclusively using the rotation curve of the Galaxy is not enough to provide a robust estimate of $\rho_{{\rm DM},\odot}$. For all the models that we study without the presence of an additional thin component, our resulting estimates of the local dark matter density take values in the range $\rho_{{\rm DM},\odot} \simeq \text{0.3--0.4}\,\mathrm{GeV/cm^3}$, consistent with many of the estimates in the literature.