Comparing the Spatial Correlation of Binary Black Hole Mergers to Large-scale Structure through the Illustris Simulation
Shaniya Jarrett, Kelly Holley‐Bockelmann, Robert J. Scherrer · The Astrophysical Journal · 2026
Abstract Gravitational waves 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 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, with power-law slopes ranging from γ m = 1.63–1.71 for mergers and γ g = 1.51–1.75 for galaxies, and that the bias is relatively constant as a function of separation. We note that the 75 Mpc h −1 box size limits our ability to probe scales beyond ∼20 Mpc h −1 , and our conclusions about linear bias should be applied to those scales only. 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.