The local high velocity tail and the Galactic escape speed

Abstract

We model the fastest moving (v_tot > 300 km/s) 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 M_200,tot ~ 10^12 M_Sun.

13 pages, 10 Figures. MNRAS accepted

References in corpus (14)

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Cited by in corpus (13)

• All-Sky Dynamical Response of the Galactic Halo to the Large Magellanic Cloud
• Gas accretion and galactic fountain flows in the Auriga cosmological simulations: angular momentum and metal re-distribution
• The effects of dynamical substructure on Milky Way mass estimates from the high velocity tail of the local stellar halo
• Probing dark photons with plasma haloscopes
• Gaia EDR3 in 6D: Searching for unbound stars in the Galaxy
• Discovery of Magellanic Stellar Debris in the H3 Survey
• Charting Galactic Accelerations: When and How to Extract a Unique Potential from the Distribution Function
• Flying far and fast: the distribution of distant hypervelocity star candidates from Gaia DR2 data
• A Versatile and Accurate Method for Halo Mass Determination from Phase-Space Distribution of Satellite Galaxies
• Deep and fast Solar System flybys: The controversial case of WD 0810-353
• The outskirts of M33: Tidally induced distortions versus signatures of gas accretion
• Milky Way Mass Through Escape Velocity Curve from LAMOST K Giants
• Timing Mass of the Local Group