Estimation of the Tilt of the Stellar Velocity Ellipsoid from RAVE and Implications for Mass Models

Abstract

We present a measure of the inclination of the velocity ellipsoid at 1 kpc below the Galactic plane using a sample of red clump giants from the RAVE DR2 release. We find that the velocity ellipsoid is tilted towards the Galactic plane with an inclination of 7.3 +/-1.8 degree. We compare this value to computed inclinations for two mass models of the Milky Way. We find that our measurement is consistent with a short scale length of the stellar disc (Rd ~2 kpc) if the dark halo is oblate or with a long scale length (Rd~3 kpc) if the dark halo is prolate. Once combined with independent constraints on the flattening of the halo, our measurement suggests that the scale length is approximately halfway between these two extreme values, with a preferred range [2.5-2.7] kpc for a nearly spherical halo. Nevertheless, no model can be clearly ruled out. With the continuation of the RAVE survey, it will be possible to provide a strong constraint on the mass distribution of the Milky Way using refined measurements of the orientation of the velocity ellipsoid.

Accepted for publication in MNRAS, 10 pages, 9 figures, 2 tables

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• The age-velocity dispersion relation of the Galactic discs from LAMOST-Gaia data
• Double-lined Spectroscopic Binary Stars in the Radial Velocity Experiment Survey
• The kinematics of late type stars in the solar cylinder studied with SDSS data
• Measuring the local dark matter density with LAMOST DR5 and Gaia DR2
• The stability of stellar disks in Milky-Way sized dark matter halos
• Jeans modelling of the Milky Way's nuclear stellar disc
• Local stellar formation history from the 40 pc white dwarf sample
• Stellar over-densities in the halo: the extent of the Virgo over-density
• The velocity ellipsoid in the Galactic disc using Gaia DR1
• The Galactic disc phase spirals at different Galactic positions revealed by Gaia and LAMOST data
• The Galactic thin and thick disk
• Kinematics of the Galactic disk from LAMOST Dwarf sample
• Galactic Kinematics Derived from Data in the RAVE5, UCAC4, PPMXL, and Gaia TGAS Catalogs
• Miyamoto-Nagai discs embedded in the Binney logarithmic potential: analytical solution of the two-integrals Jeans equations
• A method to calculate the local density distribution of the Galaxy from the Tycho-Gaia Astrometric Solution data
• Asymmetries in random motions of neutral Hydrogen gas in spiral galaxies