Dynamical Tidal Locking Theory: A new source of the Spin of Dark Matter
  Halos
  We revisit the question of what mechanism is responsible for the spins of
halos of dark matter. The answer to this question is of high importance for
modeling galaxy intrinsic alignment, which can potentially contaminate current
and future lensing data. In particular, we show that when the dark matter halos
pass nearly by each other in dense environments-- namely halo assemblies-- they
swing and spin each other via exerting mutual tidal torques. We show that this
has a significant contribution to the spin of dark matter halos comparable to
that of calculated by the so-called tidal torque theory (TTT). We use the
results of state-of-the-art simulation of Illutris to check the prediction of
this theory against the simulation data.
