The RAVE survey: the Galactic escape speed and the mass of the Milky Way

¹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
e-mail: tilmann.piffl@physics.ox.ac.uk
² Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford OX1 3NP, UK
³ Institute for Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁴ Dept. of Astronomy and Astrophysics, Villanova University, 800 E Lancaster Ave, Villanova, PA 19085, USA
⁵ Observatoire astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l’Université, 67000 Strasbourg, France
⁶ Sydney Institute for Astronomy, University of Sydney, School of Physics A28, NSW, 2088, Australia
⁷ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12–14, 69120 Heidelberg, Germany
⁸ Research School of Astronomy and Astrophysics, Australian National University, Cotter Rd., ACT 2611 Weston, Australia
⁹ Jeremiah Horrocks Institute, University of Central Lancashire, Preston, PR1 2HE, UK
¹⁰ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
¹¹ National Institute of Astrophysics INAF, Astronomical Observatory of Padova, 36012 Asiago, Italy
¹² Senior CIfAR Fellow, University of Victoria, Victoria BC, V8P 5C2, Canada
¹³ Department of Physics, Macquarie University, NSW, 2109 Sydney, Australia
¹⁴ Research Centre for Astronomy, Astrophysics and Astrophotonics, Macquarie University, NSW, 2109 Sydney, Australia
¹⁵ Australian Astronomical Observatory, PO Box 296, NSW 1710 Epping, Australia
¹⁶ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, RH5 6NT, UK
¹⁷ Australian Astronomical Observatory, PO Box 915, NSW 1670 North Ryde, Australia
¹⁸ Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
¹⁹ University of Ljubljana, Faculty of Mathematics and Physics, Jadranska 19, 1000 Ljubljana, Slovenia
²⁰ Center of excellence space-si, Askerceva 12, 1000 Ljubljana, Slovenia

Received: 23 August 2013
Accepted: 12 November 2013

Abstract

We made new estimates of the Galactic escape speed at various Galactocentric radii using the latest data release of the RAdial Velocity Experiment (RAVE DR4). Compared to previous studies we have a database that is larger by a factor of 10, as well as reliable distance estimates for almost all stars. Our analysis is based on statistical analysis of a rigorously selected sample of 90 high-velocity halo stars from RAVE and a previously published data set. We calibrated and extensively tested our method using a suite of cosmological simulations of the formation of Milky Way-sized galaxies. Our best estimate of the local Galactic escape speed, which we define as the minimum speed required to reach three virial radii R₃₄₀, is 533⁺⁵⁴_-41 km s^-1 (90% confidence), with an additional 4% systematic uncertainty, where R₃₄₀ is the Galactocentric radius encompassing a mean overdensity of 340 times the critical density for closure in the Universe. From the escape speed we further derived estimates of the mass of the Galaxy using a simple mass model with two options for the mass profile of the dark matter halo: an unaltered and an adiabatically contracted Navarro, Frenk & White (NFW) sphere. If we fix the local circular velocity, the latter profile yields a significantly higher mass than the uncontracted halo, but if we instead use the statistics for halo concentration parameters in large cosmological simulations as a constraint, we find very similar masses for both models. Our best estimate for M₃₄₀, the mass interiorto R₃₄₀ (dark matter and baryons), is 1.3^+0.4_-0.3 × 10¹² M_⊙ (corresponds to M₂₀₀ = 1.6^+0.5_-0.4 × 10¹² M_⊙). This estimate is in good agreement with recently published, independent mass estimates based on the kinematics of more distant halo stars and the satellite galaxy Leo I.