A novel determination of the local dark matter density

Abstract

We present a novel study on the problem of constructing mass models for the Milky Way, concentrating on features regarding the dark matter halo component. We have considered a variegated sample of dynamical observables for the Galaxy, including several results which have appeared recently, and studied a 7- or 8-dimensional parameter space - defining the Galaxy model - by implementing a Bayesian approach to the parameter estimation based on a Markov Chain Monte Carlo method. The main result of this analysis is a novel determination of the local dark matter halo density which, assuming spherical symmetry and either an Einasto or an NFW density profile is found to be around 0.39 GeV cm$^{-3}$ with a 1-$σ$ error bar of about 7%; more precisely we find a $ρ_{DM}(R_0) = 0.385 \pm 0.027 \rm GeV cm^{-3}$ for the Einasto profile and $ρ_{DM}(R_0) = 0.389 \pm 0.025 \rm GeV cm^{-3}$ for the NFW. This is in contrast to the standard assumption that $ρ_{DM}(R_0)$ is about 0.3 GeV cm$^{-3}$ with an uncertainty of a factor of 2 to 3. A very precise determination of the local halo density is very important for interpreting direct dark matter detection experiments. Indeed the results we produced, together with the recent accurate determination of the local circular velocity, should be very useful to considerably narrow astrophysical uncertainties on direct dark matter detection.

Figures (11)

• Figure 1: Marginal posterior pdf of the Galactic model parameters (Einasto profile). In each plot the green vertical line represents the mean of the corresponding parameter while the red dashed line its best fit value. The yellow (blue) bar above the curves indicates the largest interval including the 68% (95%) of the total probability.
• Figure 2: Marginal posterior pdf of the Galactic model parameters (NFW profile). In each plot the green vertical line represents the mean of the corresponding parameter while the red dashed line its best fit value. The yellow (blue) bar above the curves indicates the largest interval including the 68% (95%) of the total probability.
• Figure 3: Marginal posterior pdf of a few derived quantities (Einasto profile). In each plot the green vertical line represents the mean of the corresponding parameter while the red dashed line its best fit value. The yellow (blue) bar above the curves indicates the largest interval including the 68% (95%) of the total probability.
• Figure 4: Two dimensional marginal posterior pdf in the planes spanned by the combinations of the Galactic model parameters which determine the dark matter halo in the case of an Einasto profile. The normalization is such that at the maximum the posterior pdf is equal to one. The black dots correspond to the means of the plotted posterior pdf. One and two sigma contours are also shown.
• Figure 5: Two dimensional marginal posterior pdf in the planes spanned by the combinations of the Galactic model parameters which determine the dark matter halo in the case of a NFW profile. The normalization is such that at the maximum the posterior pdf is equal to one. The black dots correspond to the means of the plotted posterior pdf. One and two sigma contours are also shown.