Joint constraints on the Galactic dark matter halo and Galactic Centre from hypervelocity stars

The mass assembly history of the Milky Way can inform both theory of galaxy formation and the underlying cosmological model. Thus, observational constraints on the properties of both its baryonic and dark matter contents are sought. Here, we show that hypervelocity stars (HVSs) can in principle provide such constraints. We model the observed velocity distribution of HVSs, produced by tidal break-up of stellar binaries caused by Sgr A*. Considering a Galactic Centre (GC) binary population consistent with that inferred in more observationally accessible regions, a fit to current HVS data with significance level > 5 per cent can only be obtained if the escape velocity from the GC to 50 kpc is V-G less than or similar to 850 km s(-1), regardless of the enclosed mass distribution. When a Navarro, Frenk and White matter density profile for the dark matter halo is assumed, haloes with V-G less than or similar to 850 km s(-1) are in agreement with predictions in the Lambda cold dark matter model and a subset of models around M-200 similar to 0.5-1.5 x 10(12) M-circle dot and r(s) less than or similar to 35 kpc can also reproduce Galactic circular velocity data. HVS data alone cannot currently exclude potentials with V-G > 850 km s(-1). Finally, specific constraints on the halo mass from HVS data are highly dependent on the assumed baryonic mass potentials. This first attempt to simultaneously constrain GC and dark halo properties is primarily hampered by the paucity and quality of data. It nevertheless demonstrates the potential of our method, that may be fully realized with the ESA Gaia mission.