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 VG ≲ 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 VG ≲ 850 km s-1 are in agreement with predictions in the ≲ cold dark matter model and a subset of models around M200 ~ 0.5-1.5 × 1012M⊙ and rs ≲ 35 kpc can also reproduce Galactic circular velocity data. HVS data alone cannot currently exclude potentials with VG > 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.
Bibliographical noteFunding Information:
We thank S. de Mink and R. Schödel for a careful reading of the manuscript and O. Gnedin, M. Viola, H. Perets, E. Starkenburg, J. Navarro, A. Helmi, S. Kobayashi and A. Brown for useful discussions and comments. We also thank the anonymous referee for the careful reading of the manuscript and his/her useful suggestions. EMR and TM acknowledge the support from NWO TOP grant Module 2, project number 614.001.401.
© 2017 The Authors.
- Dark matter
- Galaxy: Centre
- Galaxy: halo
- Methods: analytical
- Stars: kinematics and dynamics