The Galactic Disk Phase Spirals at Different Galactic Positions Revealed by Gaia and LAMOST Data
Wang, H. -F.; Huang, Y.; Chen, B. -Q.; Wang, C.; Zhang, H. -W.; Xiang, M. -S.; Yuan, H. -B.; Yang, Y.; Liu, X. -W.; Tian, Z. -J.; Zhang, M.; Wu, Y. -Q.
China, Germany
Abstract
We have investigated the distributions of stellar azimuthal and radial velocity components V Φ and V R in the vertical position-velocity plane Z-V Z across the Galactic disk of 6.34 ≲ R ≲ 12.34 kpc and | {{Φ }}| ≲ 7\buildrel{\circ}\over{.} 5 using a Gaia and Gaia-LAMOST sample of stars. As found in previous works, the distributions exhibit significant spiral patterns. The V R distributions also show clear quadrupole patterns, which are the consequence of the well-known tilt of the velocity ellipsoid. The observed spiral and quadrupole patterns in the phase space plane vary strongly with radial and azimuthal positions. The phase spirals of V Φ become more and more relaxed as R increases. The spiral patterns of V Φ and V R and the quadrupole patterns of V R are strongest at -2° < Φ < 2° but negligible at 4° < Φ < 6° and -6° < Φ < -4°. Our results suggest an external origin of the phase spirals. In this scenario, the intruder, most likely the previously well-known Sagittarius dwarf galaxy, passed through the Galactic plane in the direction toward either Galactic center or anti-center. The azimuthal variations of the phase spirals also help us constrain the passage duration of the intruder. A detailed model is required to reproduce the observed radial and azimuthal variations of the phase spirals of V Φ and V R .