The Supersonic Project: rotational effects of supersonic motions on the first structures in the Universe

TL;DR

This study investigates how supersonic relative velocities between dark matter and baryons at high redshift influence the angular momentum and structure of the first cosmic objects, revealing increased spin and misalignment effects.

Contribution

It provides new insights into the impact of stream velocity on the angular momentum and morphology of early Universe structures, including the first haloes and SIGOs.

Findings

Gas spin parameter increases with stream velocity.

Angular momentum vectors of DM and gas are often misaligned.

SIGOs have larger spin parameters than their dark matter counterparts.

Abstract

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.