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. ReidA. Siviero, M. Steinmetz, F. Watson, R. F.G. Wyse, T. Zwitter

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    90 Citations (Scopus)


    Using a sample of 213713 stars from the Radial Velocity Experiment (RAVE) survey, limited to a distance of 2kpc from the Sun and to |z| < 1kpc, 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.

    Original languageEnglish
    Pages (from-to)2026-2032
    Number of pages7
    JournalMonthly Notices of the Royal Astronomical Society
    Issue number3
    Publication statusPublished - Apr 2011


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