The Supersonic Project: To cool or not to cool Supersonically Induced Gas Objects (SIGOs)?

TL;DR

This study investigates how atomic cooling influences the physical properties of SIGOs, primordial gas structures in the early universe, revealing that gravity dominates their characteristics while cooling affects their star-forming potential.

Contribution

The paper demonstrates through simulations that SIGO properties are primarily governed by gravity, with atomic cooling significantly increasing cold gas fractions, impacting early star formation.

Findings

SIGOs' density, temperature, and shape are driven by gravity rather than cooling.

Atomic cooling increases the cold gas fraction in SIGOs.

SIGOs provide potential sites for early star formation.

Abstract

Supersonically Induced Gas Objects (SIGOs) primarily form in the early Universe, outside of dark matter halos due to the presence of a relative stream velocity between baryons and dark matter. These structures may be the progenitors of globular clusters. Since SIGOs are made out of pristine gas, we investigate the effect of atomic cooling on their properties. We run a suite of simulations by using the moving-mesh code {\sc arepo}, with and without baryon-dark matter relative velocity and with and without the effects of atomic cooling. We show that SIGO's density, temperature, and prolateness are determined by gravitational interactions rather than cooling. The cold gas fraction in SIGOs is much higher than that of dark matter halos. Specifically, we show that the SIGO's characteristic low temperature and extreme high gas density forges a nurturing ground for the earliest star formation sites.