On the estimation of the local dark matter density using the rotation curve of the Milky Way

The rotation curve of the Milky Way is commonly used to estimate the local dark matter density ρDM,solar. 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 ρDM,solar. For this purpose we analyze the precise circular velocity curve measurement of the Milky Way up to ~ 25 kpc from the Galactic centre obtained from Gaia DR2 [1]. We find that the estimated value of ρDM,solar stays robust to reasonable changes in the spherical dark matter halo. However, we show that ρDM,solar is affected by the choice of the model for the underlying baryonic components. In particular, we find that ρDM,solar 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 ρDM,solar 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 ρDM,solar 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 ρDM,solar. 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 ρDM,solar simeq 0.3-0.4 GeV/cm³, consistent with many of the estimates in the literature.