Galactic kinematics with RAVE data

I. The distribution of stars towards the Galactic poles

¹ Observatoire Astronomique de Strasbourg, Strasbourg, France e-mail: veltz@astro.u-strasbg.fr
² RSAA, Mount Stromlo Observatory, Canberra, Australia
³ Astrophysikalisches Institut Potsdam, Potsdam, Germany
⁴ Rudolf Peierls Centre for Theoretical Physics, University of Oxford, UK
⁵ School of Physics, University of Sydney, Australia
⁶ University of Central Lancashire, Preston, UK
⁷ Institute of Astronomy, University of Cambridge, UK
⁸ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Heidelberg, Germany
⁹ Astronomical Institute of the University of Basel, Basel, Switzerland
¹⁰ Kapteyn Astronomical Institute, University of Groningen, Groningen, The Netherlands
¹¹ INAF Osservatorio Astronomico di Padova, Asiago, Italy
¹² University of Victoria, Victoria, Canada
¹³ Anglo Australian Observatory, Sydney, Australia
¹⁴ Macquarie University, Sydney, Australia
¹⁵ Johns Hopkins University, Baltimore MD, USA
¹⁶ University of Ljubljana, Department of Physics, Ljubljana, Slovenia

Received: 15 December 2006
Accepted: 18 December 2007

Abstract

We analyze the distribution of G and K type stars towards the Galactic poles using RAVE and ELODIE radial velocities, 2MASS photometric star counts, and UCAC2 proper motions. The combination of photometric and 3D kinematic data allows us to disentangle and describe the vertical distribution of dwarfs, sub-giants and giants and their kinematics.
We identify discontinuities within the kinematics and magnitude counts that separate the thin disk, thick disk and a hotter component. The respective scale heights of the thin disk and thick disk are 225 ± 10 pc and 1048 ± 36 pc. We also constrain the luminosity function and the kinematic distribution function. The existence of a kinematic gap between the thin and thick disks is incompatible with the thick disk having formed from the thin disk by a continuous process, such as scattering of stars by spiral arms or molecular clouds. Other mechanisms of formation of the thick disk such as “created on the spot” or smoothly “accreted” remain compatible with our findings.