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 and the gas components 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 DM 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.