The Supersonic Project: SIGOs, a Proposed Progenitor to Globular Clusters, and their Connections to Gravitational Wave Anisotropies

TL;DR

This paper predicts the large-scale distribution of SIGOs, potential globular cluster progenitors, using semi-analytical methods and simulations, and explores their connection to gravitational wave anisotropies.

Contribution

It introduces a semi-analytical approach to estimate SIGO abundances on large scales and links these to observable globular cluster and gravitational wave anisotropies.

Findings

SIGO number density aligns with observed globular cluster densities.

Large-scale SIGO variations could be observable by JWST.

SIGOs may cause detectable anisotropies in gravitational wave signals.

Abstract

Supersonically Induced Gas Objects (SIGOs), are structures with little to no dark matter component predicted to exist in regions of the Universe with large relative velocities between baryons and dark matter at the time of recombination. They have been suggested to be the progenitors of present-day globular clusters. Using simulations, SIGOs have been studied on small scales (around 2 Mpc), where these relative velocities are coherent. However, it is challenging to study SIGOs using simulations on large scales due to the varying relative velocities at scales larger than a few Mpc. Here, we study SIGO abundances semi-analytically: using perturbation theory, we predict the number density of SIGOs analytically, and compare these results to small-box numerical simulations. We use the agreement between the numerical and analytic calculations to extrapolate the large-scale variation of SIGO abundances over different stream velocities. As a result, we predict similar large-scale variations of objects with high gas densities before reionization that could possibly be observed by JWST. If indeed SIGOs are progenitors of globular clusters, then we expect a similar variation of globular cluster abundances over large scales. Significantly, we find that the expected number density of SIGOs is consistent with observed globular cluster number densities. As a proof-of-concept, and because globular clusters were proposed to be natural formation sites for gravitational wave sources from binary black hole (BBH) mergers, we show that SIGOs should imprint an anisotropy on the gravitational wave signal on the sky, consistent with SIGOs' distribution.