The local rotation curve of the Milky Way based on SEGUE and RAVE data

¹ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12–14, 69120 Heidelberg, Germany
e-mail: sysoliatina@uni-heidelberg.de
² School of Physics and Technology, V. N. Karazin Kharkiv National University, 4 Svobody Sq., Kharkiv 61022, Ukraine
³ Institute of Astronomy, V. N. Karazin Kharkiv National University, 35 Sumska Str., Kharkiv 61022, Ukraine
⁴ Department of Aerospace Engineering Sciences, University of Colorado at Boulder, 429 UCB, Boulder, CO 80309, USA
⁵ Department of Physics, University of Hong Kong, Hong Kong SAR, PR China
⁶ Laboratory for Space Research, University of Hong Kong, Hong Kong SAR, PR China
⁷ INAF - Astronomical Observatory of Padova, 36012 Asiago (VI), Italy
⁸ E. A. Milne Centre for Astrophysics, University of Hull, Hull HU6 7RX, UK
⁹ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking RH5 6NT, UK
¹⁰ Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109, Australia
¹¹ Western Sydney University, Locked bag 1797, Penrith South DC, NSW 2751, Australia
¹² Senior CIfAR Fellow, University of Victoria, Victoria BC V8P 5C2, Canada
¹³ Australian Astronomical Observatory, PO Box 915, North Ryde, NSW 1670, Australia
¹⁴ Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006, Australia
¹⁵ Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana, Slovenia
¹⁶ Saint Martin’s University, 5000 Abbey Way, Lacey, WA 98503, USA
¹⁷ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
¹⁸ Leibniz Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482, Potsdam, Germany

Received: 8 May 2017
Accepted: 20 February 2018

Abstract

Aims. We construct the rotation curve of the Milky Way in the extended solar neighbourhood using a sample of Sloan Extension for Galactic Understanding and Exploration (SEGUE) G-dwarfs. We investigate the rotation curve shape for the presence of any peculiarities just outside the solar radius as has been reported by some authors.

Methods. Using the modified Strömberg relation and the most recent data from the RAdial Velocity Experiment (RAVE), we determine the solar peculiar velocity and the radial scale lengths for the three populations of different metallicities representing the Galactic thin disc. Subsequently, with the same binning in metallicity for the SEGUE G-dwarfs, we construct the rotation curve for a range of Galactocentric distances from 7 to 10 kpc. We approach this problem in a framework of classical Jeans analysis and derive the circular velocity by correcting the mean tangential velocity for the asymmetric drift in each distance bin. With SEGUE data we also calculate the radial scale length of the thick disc taking as known the derived peculiar motion of the Sun and the slope of the rotation curve.

Results. The tangential component of the solar peculiar velocity is found to be V _⊙ = 4.47 ± 0.8 km s⁻¹ and the corresponding scale lengths from the RAVE data are R_d(0 < [Fe/H] < 0.2) = 2.07 ± 0.2 kpc, R_d(−0.2 < [Fe/H] < 0) = 2.28 ± 0.26 kpc and R_d(−0.5 < [Fe/H] <−0.2) = 3.05 ± 0.43 kpc. In terms of the asymmetric drift, the thin disc SEGUE stars are demonstrated to have dynamics similar to the thin disc RAVE stars, therefore the scale lengths calculated from the SEGUE sample have close values: R_d(0 < [Fe/H] < 0.2) = 1.91 ± 0.23 kpc, R_d(−0.2 < [Fe/H] < 0) = 2.51 ± 0.25 kpc and R_d(−0.5 < [Fe/H] <−0.2) = 3.55 ± 0.42 kpc. The rotation curve constructed through SEGUE G-dwarfs appears to be smooth in the selected radial range 7 kpc < R < 10 kpc. The inferred power law index of the rotation curve is 0.033 ± 0.034, which corresponds to a local slope of dV _c∕dR = 0.98 ± 1 km s⁻¹ kpc⁻¹. The radial scale length of the thick disc is 2.05 kpc with no essential dependence on metallicity.

Conclusions. The local kinematics of the thin disc rotation as determined in the framework of our new careful analysis does not favour the presence of a massive overdensity ring just outside the solar radius. We also find values for solar peculiar motion, radial scale lengths of thick disc, and three thin disc populations of different metallicities as a side result of this work.