Ripple patterns in in-plane velocities of OB stars from LAMOST and Gaia

Abstract

With about 12 000 OB type stars selected from the LAMOST and Gaia survey, we study their 3 dimensional velocity distribution over the range of galactocentric radius from 6 to 15 kpc in the Galactic disk plane. A clear ripple pattern in the radial velocity ($V_R$) map is shown. The median $V_R$ reaches $-8$ km s${}^{-1}$ at $R\sim 9$ kpc, then increases to $\sim 0$ km s${}^{-1}$ at $R\sim 12$ kpc, and later declines to below $-10$ km s${}^{-1}$ beyond $R\sim 13$ kpc. The median azimuthal velocity ($V_{\varphi }$) map shows a similar pattern but has roughly $1/4$ phase difference with the radial velocity. Although the ripple of negative $V_R$ at $\sim 9$ kpc extends to about 40${}^{\circ }$ in the azimuth angle, it does not align with either the Local or the Perseus spiral arm. Moreover, the farther ripple beyond 13 kpc does not match the Outer spiral arm either. This indicates that the non-axisymmetric kinematic features are not induced by perturbations of known spiral structures. The central rotating bar can not lead to such patterns in the outer disk either. External perturbation of a dwarf galaxy or a dark matter sub-halo can induce such patterns but requires more evidence from both observations and simulations. The $V_{\varphi }$ map in the $Z$--$V_Z$ plane of the OB stars is also investigated. Despite asymmetry to some degree, no spiral pattern is found. This is reasonable since most of the OB stars have ages much younger than 100 Myrs, which is smaller than one orbital period around the Galactic center.

8 pages, 5 figures; accepted for publication by ApJL on Jan 26, 2019

References in corpus (8)

• The Gaia mission
• A Grid of NLTE Line-Blanketed Model Atmospheres of Early B-type Stars
• Rings and Radial Waves in the Disk of the Milky Way
• Radial and vertical flows induced by galactic spiral arms: likely contributors to our "wobbly Galaxy''
• A Possible Extension of the Scutum-Centaurus Arm into the Outer Second Quadrant
• The Vertical Structure and Kinematics of Grand Design Spirals
• The peculiar in-plane velocities in the outer disc of the Milky Way
• The local spiral arm in the LAMOST-Gaia common stars?

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