Comparing the Spatial Correlation of Binary Black Hole Mergers to Large-Scale Structure through the Illustris Simulation

TL;DR

This study compares the spatial clustering of massive binary black hole mergers to galaxy distributions using the IllustrisTNG simulation, highlighting their potential for cosmological insights with LISA.

Contribution

It demonstrates that MBBH mergers are more strongly clustered than galaxies at small scales, providing a new way to probe large-scale structure with gravitational wave data.

Findings

MBBH mergers show stronger clustering than galaxies at <10 Mpc/h.

The bias of MBBH mergers remains relatively constant across scales.

Results suggest MBBH distributions can inform galaxy distribution and aid in foreground subtraction.

Abstract

Gravitational waves (GWs) have provided a new lens through which to view the universe beyond traditional electromagnetic methods. The upcoming space-based gravitational wave mission, Laser Interferometer Space Antenna (LISA), will give us the first glimpse of the sky in mHz gravitational waves, a waveband that contains a rich variety of sources including massive binary black hole (MBBH) mergers. In this work, we investigate the spatial distribution of MBBH mergers versus the galaxy distribution to determine how well LISA could be used as a unique and independent probe of large-scale structure. We compare the two-point correlation function (2pt CF) of MBBH mergers to that of galaxies within the cosmological hydrodynamic simulation IllustrisTNG. Our results show that MBBH mergers exhibit stronger clustering than galaxies at scales less than 10 Mpc $h^{-1}$, particularly at higher redshifts, and that the bias is relatively constant as a function of separation. These findings imply that the spatial distribution of MBBH mergers detectable by LISA could inform the observed galaxy distribution. In addition, this implies that searches for a cosmological background in LISA data could use a prior derived from large-scale structure observations to subtract the MBBH foreground.