The Local Dark Matter Density

Abstract

I review current efforts to measure the mean density of dark matter near the Sun. This encodes valuable dynamical information about our Galaxy and is also of great importance for ‘direct detection ’ dark matter experiments. I discuss theoretical expectations in our current cosmology; the theory behind mass modelling of the Galaxy; and I show how combining local and global measures probes the shape of the Milky Way dark matter halo and the possible presence of a ‘dark disc’. I stress the strengths and weaknesses of different methodologies and highlight the contin-uing need for detailed tests on mock data – particularly in the light of recently discovered evidence for disequilibria in the Milky Way disc. I collate the latest mea-surements of ρdm and show that, once the baryonic surface density contribution Σb is normalised across different groups, there is remarkably good agreement. Compiling data from the literature, I estimate Σb = 54.2 ± 4.9 M pc−2, where the dominant source of uncertainty is in the HI gas contribution. Assuming this contribution from the baryons, I highlight several recent measurements of ρdm in order of increasing