The peculiar in-plane velocities in the outer disc of the Milky Way

Abstract

We present the peculiar in-plane velocities derived from the LAMOST red clump stars, which are purified and separated by a novel approach into two groups with different ages. The samples are mostly contributed around the Galactic anti-centre direction such that we are able to map the radial profiles of the radial and azimuthal velocities in the outer disc. From the variations of the in-plane velocities with the Galactocentric radius for the younger and older populations, we find that both radial and azimuthal velocities are not axisymmetric at $8<R<14kpc$. The two red clump populations show that the mean radial velocity is negative within $R\sim 9kpc$ and positive beyond. This is likely because of the perturbation induced by the rotating bar. The cross-zero radius, $R\sim 9$\, kpc, essentially indicates the rough location of the outer Lindblad resonance (OLR) radius. Given the circular speed of 238\,km${\mathrm{s}}^{-1}$, then the pattern speed of the bar can be approximated as $45$\,km${\mathrm{s}}^{-1}\mathrm{kp}{\mathrm{c}}^{-1}$. The young red clump stars show larger mean radial velocity than the old population by about 3$km{\mathrm{s}}^{-1}$ between $R\sim 9$ and 12\,kpc. This is possibly because the younger population is more sensitive to the perturbation than the older one. The radial profiles of the mean azimuthal velocity for the two populations show an interesting U-shape, i.e. at $R<10.5kpc$, the azimuthal velocity declines with $R$ by about 10$km{\mathrm{s}}^{-1}$, while at $R>10.5$ it increases with $R$ to 240-245$km{\mathrm{s}}^{-1}$. It is not clear why the mean azimuthal velocity shows the U-shape along the Galactic anti-centre direction. Meanwhile, the azimuthal velocity for the younger population is slightly larger than the older one and the difference moderately declines with $R$. Beyond $R\sim 12kpc$, the azimuthal velocities for the two populations are indistinguishable.

arXiv commentrepeat with arXiv:1603.06262

References in corpus (34)

• emcee: The MCMC Hammer
• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• The Eleventh and Twelfth Data Releases of the Sloan Digital Sky Survey: Final Data from SDSS-III
• Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way
• Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars
• LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) The survey science plan
• The Effect of the Outer Lindblad Resonance of the Galactic Bar on the Local Stellar Velocity Distribution
• Galactoseismology: Discovery of Vertical Waves in the Galactic Disk
• NON-AXISYMMETRIC STRUCTURES IN THE STELLAR DISKS OF GALAXIES
• Galactic Rotation and Solar Motion from Stellar Kinematics
• The wobbly Galaxy: kinematics north and south with RAVE red clump giants
• Red giant masses and ages derived from carbon and nitrogen abundances
• Asteroseismic classification of stellar populations among 13000 red giants observed by Kepler
• Rings and Radial Waves in the Disk of the Milky Way
• Vertical density waves in the Milky Way disc induced by the Sagittarius Dwarf Galaxy
• The Milky Way Tomography with SDSS: III. Stellar Kinematics
• The RAdial Velocity Experiment (RAVE): Third Data Release
• Substructure in bulk velocities of Milky Way disk stars
• Radial and vertical flows induced by galactic spiral arms: likely contributors to our "wobbly Galaxy''
• Revisiting the Tale of Hercules: how stars orbiting the Lagrange points visit the Sun
• The properties of the local spiral arms from RAVE data: two-dimensional density wave approach
• Detection of a radial velocity gradient in the extended local disc with RAVE
• Slicing and dicing the Milky Way disk in SDSS
• The K giant stars from the LAMOST survey data I: identification, metallicity, and distance
• More dynamical models of our Galaxy
• The power spectrum of the Milky Way: Velocity fluctuations in the Galactic disk
• The Vertical Structure and Kinematics of Grand Design Spirals
• Spiral and bar driven peculiar velocities in Milky Way sized galaxy simulations
• Made-to-measure galaxy models - III Modelling with Milky Way observations
• A Schwarzschild model of the Galactic bar with initial density from N-body simulations
• The site conditions of the Guo Shou Jing Telescope
• Red Clump Stars from the LAMOST data I: identification and distance
• Radial motions in disk stars: ellipticity or secular flows?
• The dangers of deprojection of proper motions

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