http://arxiv.org/abs/1608.02000
The mass assembly history of the Milky Way is an outstanding issue that can inform both theory of galaxy formation and the underlying cosmological model. For this reason, 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 observed in more accessible star forming regions, a marginally acceptable fit to current HVS data can be obtained only if the escape velocity from the GC to 50 kpc is $V_{\rm G} \lower.5ex\hbox{$\; \buildrel < \over \sim \;$} 800$ km/s, regardless of the enclosed mass distribution. When a NFW matter density profile for the dark matter halo is assumed, a total halo mass $M_{\rm h} < 1.2 \times 10^{12} M_{\odot}$ and scale radius $r_{\rm s} < 35$ kpc are favoured, if the observed circular velocity profile is also to be reproduced. These values are in agreement with results from the EAGLE hydro-cosmological simulation. Nevertheless, HVS data alone cannot currently exclude potentials with $V_{\rm G} > 800$ km/s. Models in this region, however, would not reproduce circular velocity data, would require a binary population in the GC increasingly different from those observed elsewhere and dark matter haloes increasingly inconsistent with predictions in the $\Lambda$CDM model. 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 realised with the ESA Gaia mission.
E. Rossi, T. Marchetti, M. Cacciato, et. al.
Tue, 9 Aug 16
58/71
Comments: 12 pages, 6 figures, submitted to MNRAS on July 12 2016
You must be logged in to post a comment.