The Galactic disc phase spirals at different Galactic positions revealed by Gaia and LAMOST data. (arXiv:1903.09982v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Wang_C/0/1/0/all/0/1">C. Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Huang_Y/0/1/0/all/0/1">Y. Huang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yuan_H/0/1/0/all/0/1">H.-B. Yuan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Xiang_M/0/1/0/all/0/1">M.-S. Xiang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chen_B/0/1/0/all/0/1">B.-Q. Chen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_H/0/1/0/all/0/1">H.-F. Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wu_Y/0/1/0/all/0/1">Y.-Q. Wu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_H/0/1/0/all/0/1">H.-W. Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tian_Z/0/1/0/all/0/1">Z.-J. Tian</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yang_Y/0/1/0/all/0/1">Y. Yang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_M/0/1/0/all/0/1">M. Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Liu_X/0/1/0/all/0/1">X.-W. Liu</a>
We have investigated the distributions of stellar azimuthal and radial
velocity components $V_{Phi}$ and $V_{R}$ in the vertical position-velocity
plane $Z$-$V_{Z}$ across the Galactic disc of $6.34 lesssim R lesssim
12.34$,kpc and $|Phi| lesssim 7.5^{circ}$ 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 $V_{Phi}$ become more and more relaxed as $R$ increases. The spiral
patterns of $V_{Phi}$ and $V_{R}$ and the quadrupole patterns of $V_{R}$ are
strongest at $-2^{circ} < Phi < 2^{circ}$ but negligible at $4^{circ} <
Phi < 6^{circ}$ and $-6^{circ} < Phi < -4^{circ}$. 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 towards 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 $V_{Phi}$ and
$V_{R}$.
We have investigated the distributions of stellar azimuthal and radial
velocity components $V_{Phi}$ and $V_{R}$ in the vertical position-velocity
plane $Z$-$V_{Z}$ across the Galactic disc of $6.34 lesssim R lesssim
12.34$,kpc and $|Phi| lesssim 7.5^{circ}$ 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 $V_{Phi}$ become more and more relaxed as $R$ increases. The spiral
patterns of $V_{Phi}$ and $V_{R}$ and the quadrupole patterns of $V_{R}$ are
strongest at $-2^{circ} < Phi < 2^{circ}$ but negligible at $4^{circ} <
Phi < 6^{circ}$ and $-6^{circ} < Phi < -4^{circ}$. 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 towards 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 $V_{Phi}$ and
$V_{R}$.
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