The Galactic bar and the large scale velocity gradients in the Galactic disk

¹ Kapteyn Astronomical Institute, Rijksuniversiteit Groningen, PO Box 800 9700 AV Groningen The Netherlands
e-mail: monari@astro.rug.nl
² ESA, European Space Research and Technology Center (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
³ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany

Received: 18 February 2014
Accepted: 28 July 2014

Abstract

We investigate whether the cylindrical (galactocentric) radial velocity gradient of ~ −3 km s^-1 kpc^-1, directed radially from the Galactic center and recently observed in the stars of the solar neighborhood with the RAVE survey, can be explained by the resonant effects of the bar near the solar neighborhood. We compared the results of test particle simulations of the Milky Way with a potential that includes a rotating bar with observations from the RAVE survey. To this end we applied the RAVE selection function to the simulations and convolved these with the characteristic RAVE errors. We explored different “solar neighborhoods” in the simulations, as well as different bar models. We find that the bar induces a negative radial velocity gradient at every height from the Galactic plane, outside the outer Lindblad resonance and for angles from the long axis of the bar compatible with the current estimates. The selection function and errors do not wash away the gradient, but often make it steeper, especially near the Galactic plane, because this is where the RAVE survey is less radially extended. No gradient in the vertical velocity is present in our simulations, from which we may conclude that this cannot be induced by the bar.