First Measurement of the Cross-Correlation Angular Power Spectrum Between the Stochastic Gravitational Wave Background and Galaxy Over-Density*

We study the cross-correlation between the Stochastic Gravitational-Wave Background (SGWB) and the distribution of galaxies across the sky: we use LIGO third run (O3) SGWB data, and galaxy over-density from the Sloan Digital Sky Survey (SDSS) spectroscopic catalog and we compute the angular power spectrum of the resulting cross-correlation. Instead of integrating the SGWB signal across frequencies, we analyze the cross-correlation in 10 Hz width SGWB frequency bands to study the frequency dependence of the angular power spectrum. Finally, we compare the observed cross-correlation to the spectrum predicted by astrophysical models. We apply parameter estimation based on maximum likelihood evaluation to explore the parameter space of the theoretical models, and we set constraints on a set of (effective) astrophysical parameters describing the galactic process of gravitational wave emission.