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 rho(DM,circle dot). 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(DM,circle dot). For this purpose we analyze the precise circular velocity curve measurement of the Milky Way up to similar to 25 kpc from the Galactic centre obtained from Gaia DR2 [1]. We find that the estimated value of rho(DM,circle dot) stays robust to reasonable changes in the spherical dark matter halo. However, we show that rho(DM,circle dot) is affected by the choice of the model for the underlying baryonic components. In particular, we find that rho(DM,circle dot) 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(DM,circle dot) 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(DM,circle dot) 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(DM,circle dot). 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(DM,circle dot) similar or equal to 0.3-0.4 GeV/cm(3), consistent with many of the estimates in the literature.