Spin Alignment of Dark Matter Halos: Mad Halos
  We investigate the spin alignment of the dark matter halos by considering a
mechanism somewhat similar to tidal locking. We dubbed it Tidal Locking Theory
(TLT). While Tidal Torque Theory is responsible for the initial angular
momentum of the dark matter halos, the Tidal locking Theory explains the
angular momentum evolution during non-linear ages. Our previous work showed
that close encounters between haloes could drastically change their angular
momentum. The current manuscript argues that the tidal locking theory predicts
partial alignment between speed and the spin direction for the large high-speed
halos. To examine this prediction, we use the IllustrisTNG simulation and look
for the alignment of the halos' rotation axis. We find that the excess
probability of alignment between spin and speed is about 10 percent at $z=0$
for fast haloes; with velocities larger than twice the median. We show that
tidal torque theory predicts that the spin of a halo tends to be aligned with
the middle eigendirection of the tidal tensor. Moreover, we find that the halos
at $z=10$ are preferentially aligned with the middle eigendirection of the
tidal tensor with an excess probability of 15 percent. We show that tidal
torque theory fails to predict correct alignment at $z=0$ while it works almost
flawlessly at $z=10$.
