Mapping the Galactic disk with the LAMOST and Gaia Red clump sample. VI:
  An evidence for the long lived non-steady warp of non-gravitational scenarios
  By combining LAMOST DR4 and Gaia DR2 common red clump stars with age and
proper motion, we analyze the amplitude evolution of the stellar warp
independently of any assumption with a simple model. The greatest height of the
warp disk increases with Galactocentric distance in different populations and
it is dependent on the age: the younger stellar populations exhibit stronger
warp features than the old ones, accompanied with the warp amplitude $\gamma
({\rm age})$ decreasing with age and its first derivative $\dot{\gamma} ({\rm
age})$ is different from zero. The azimuth of line of nodes $\phi _w$ is stable
at $-$5 degree without clear time evolution, which perfectly confirms some of
previous works. All these self-consistent evidences support that our Galactic
warp should most likely be a long lived, but non-steady structure and not a
transient one, which is supporting the warp is originated from gas infall onto
the disk or other hypotheses that suppose that the warp mainly affects to the
gas, and consequently younger populations tracing the gas are stronger than the
older ones. In other words, the Galactic warp is induced by the
non-gravitational interaction over the disk models.
