The Supersonic Project: rotational effects of supersonic motions on the
  first structures in the Universe
  We introduce the "Supersonic Project," aimed at investigating the effects of
the supersonic relative velocity between dark matter (DM) and baryons at high
redshift using a combination of analytical calculations and cosmological
simulations. In this paper, we study the effect of this stream velocity on the
angular momentum of the first structures in the early Universe using
simulations. We focus on DM haloes and their gas component as well as the
recently predicted supersonically-induced gas objects (SIGOs) that arise as a
result of the stream velocity phase shift. We find that the spin parameter of
the gas component in these first haloes is increased with the stream velocity.
Moreover, we find that when the stream velocity is taken into account, the
angular momentum vectors of the DM component and the gas component are
typically misaligned and this misalignment angle has a nearly isotropic
distribution. The spin parameter value of the gas component is higher than in
the no stream velocity case, which even in the absence of cooling, may result
in more prolate objects. We also generalize the spin parameter to the SIGOs and
find that they typically have a larger spin parameter with respect to their
dark matter counterparts and that there is no correlation of the spin parameter
and the prolateness of such structures. We speculate that SIGOs may be observed
as very low luminosity objects in the early Universe and may serve as potential
progenitors of Little Blue Dot-like systems.
