The local high velocity tail and the Galactic escape speed. (arXiv:1901.02016v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Deason_A/0/1/0/all/0/1">Alis J. Deason</a> (Durham), <a href="http://arxiv.org/find/astro-ph/1/au:+Fattahi_A/0/1/0/all/0/1">Azadeh Fattahi</a> (Durham), <a href="http://arxiv.org/find/astro-ph/1/au:+Belokurov_V/0/1/0/all/0/1">Vasily Belokurov</a> (Cambridge), <a href="http://arxiv.org/find/astro-ph/1/au:+Evans_W/0/1/0/all/0/1">Wyn Evans</a> (Cambridge), <a href="http://arxiv.org/find/astro-ph/1/au:+Grand_R/0/1/0/all/0/1">Robert J. Grand</a> (MPA), <a href="http://arxiv.org/find/astro-ph/1/au:+Marinacci_F/0/1/0/all/0/1">Federico Marinacci</a> (Harvard), <a href="http://arxiv.org/find/astro-ph/1/au:+Pakmor_R/0/1/0/all/0/1">Rudiger Pakmor</a> (MPA)
We model the fastest moving local (D < 3 kpc) halo stars using cosmological simulations and 6-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 ~ 10^9 M_Sun) 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 2r_200, beyond which stars can escape. After applying our methodology to the Gaia data, we find a local (r_0=8.3 kpc) escape speed of v_esc(r_0) = 528(+24,-25) km/s. 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) x 10^12 M_Sun, c_200=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 10^12 M_Sun.
We model the fastest moving local (D < 3 kpc) halo stars using cosmological
simulations and 6-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 ~ 10^9 M_Sun) 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
2r_200, beyond which stars can escape. After applying our methodology to the
Gaia data, we find a local (r_0=8.3 kpc) escape speed of v_esc(r_0) =
528(+24,-25) km/s. 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) x 10^12 M_Sun, c_200=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 10^12 M_Sun.
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