Proceedings of the International Astronomical Union

Contributed Papers

The RAVE Survey: Constraining the Local Galactic Escape Speed

Martin C. Smitha1, G. R. Ruchtia2, A. Helmia1, R. F. G. Wysea2 and the RAVE collaborationa1

a1 Kapteyn Astronomical Institute, University of Groningen, Groningen, The Netherlands

a2 Johns Hopkins University, Baltimore MD, USA email: msmith@astro.rug.nl

Abstract

We report new constraints on the local escape speed of our Galaxy. Our analysis is based on a sample of high velocity stars from the RAVE survey and two previously published datasets (the Geneva-Copenhagen survey and the Beers et al. catalogue of metal-poor stars). We use cosmological simulations of disk galaxy formation to motivate our assumptions on the shape of the velocity distribution, allowing for a significantly more precise measurement of the escape velocity compared to previous studies. We find that the escape velocity lies within the range 492 km s−1 < vesc <594 kms (90% confidence), with a median likelihood of 536 kms. The fact that v2esc is significantly greater than 2v2circ implies that there must be a significant amount of mass exterior to the Solar circle, i.e. this convincingly demonstrates the presence of a dark halo in the Galaxy. For a simple isothermal halo, one can calculate that the minimum radial extent is ~54 kpc. We use our constraints on vesc to determine the mass of the Milky Way halo for three halo profiles. For example, an adiabatically contracted NFW halo model results in a virial mass of 1.31+0.97−0.49 × 1012Mxs2299 and virial radius of 297+60−44 kpc (90% confidence). For this model the circular velocity at the virial radius is 141+27−19kms. Although our halo masses are model dependent, we find that they are in good agreement with each other.