Journal Article

Detection of a radial velocity gradient in the extended local disc with RAVE

A. Siebert, B. Famaey, I. Minchev, G. M. Seabroke, J. Binney, B. Burnett, K. C. Freeman, M. Williams, O. Bienaymé, J. Bland-Hawthorn, R. Campbell, J. P. Fulbright, B. K. Gibson, G. Gilmore, E. K. Grebel, A. Helmi, U. Munari, J. F. Navarro, Q. A. Parker, W. A. Reid, A. Siviero, M. Steinmetz, F. Watson, R. F. G. Wyse and T. Zwitter

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 412, issue 3, pages 2026-2032
Published in print April 2011 | ISSN: 0035-8711
Published online April 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.18037.x
Detection of a radial velocity gradient in the extended local disc with RAVE

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Using a sample of 213 713 stars from the Radial Velocity Experiment (RAVE) survey, limited to a distance of 2 kpc from the Sun and to |z| < 1 kpc, we report the detection of a velocity gradient of disc stars in the fourth quadrant, directed radially from the Galactic Centre. In the direction of the Galactic Centre, we apply a simple method independent of stellar proper motions and of Galactic parameters to assess the existence of this gradient in the RAVE data. This velocity gradient corresponds to |K+C| > rsim 3 km s−1 kpc−1, where K and C are the Oort constants measuring the local divergence and radial shear of the velocity field, respectively. In order to illustrate the effect, assuming a zero radial velocity of the local standard of rest we then reconstruct the two-dimensional Galactocentric velocity maps using two different sets of proper motions and photometric distances based either on isochrone fitting or on K-band magnitudes, and considering two sets of values for the Galactocentric radius of the Sun and local circular speed. Further observational confirmation of our finding with line-of-sight velocities of stars at low latitudes, together with further modelling, should help constrain the non-axisymmetric components of the Galactic potential, including the bar, the spiral arms and possibly the ellipticity of the dark halo.

Keywords: stars: kinematics and dynamics; Galaxy: fundamental parameters; Galaxy: kinematics and dynamics

Journal Article.  4686 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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