Mon. Not. R. Astron. Soc., 485, 3514-3526 (2019/May-3)
The local high-velocity tail and the Galactic escape speed.
DEASON A.J., FATTAHI A., BELOKUROV V., EVANS N.W., GRAND R.J.J., MARINACCI F. and PAKMOR R.
Abstract (from CDS):
We model the fastest moving (v_ tot_ > 300 km s–1) local (D <= 3 kpc) halo stars using cosmological simulations and six-dimensional Gaia data. Our approach is to use our knowledge of the assembly history and phase-space distribution of halo stars to constrain the form of the high-velocity tail of the stellar halo. Using simple analytical models and cosmological simulations, we find that the shape of the high-velocity tail is strongly dependent on the velocity anisotropy and number density profile of the halo stars - highly eccentric orbits and/or shallow density profiles have more extended high-velocity tails. The halo stars in the solar vicinity are known to have a strongly radial velocity anisotropy, and it has recently been shown the origin of these highly eccentric orbits is the early accretion of a massive (M_ star_∼109M_☉) dwarf satellite. We use this knowledge to construct a prior on the shape of the high-velocity tail. Moreover, we use the simulations to define an appropriate outer boundary of 2r200, beyond which stars can escape. After applying our methodology to the Gaia data, we find a local (r0 = 8.3 kpc) escape speed of v_ esc(r0)=528+24–25 km s–1. We use our measurement of the escape velocity to estimate the total Milky Way mass, and dark halo concentration: M_200, tot_ = 1.00+0.31–0.24 ×1012 M_☉, c200=10.9+4.4–3.3. Our estimated mass agrees with recent results in the literature that seem to be converging on a Milky Way mass of M_200, tot_ ∼1012 M_☉.
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
Galaxy: fundamental parameters - Galaxy: kinematics and dynamics
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