\textit{Euclid}: From Galaxies to Gravitational Waves -- Forecasting Stochastic Gravitational Wave Background Anisotropies and Their Cross-Correlation

TL;DR

This paper predicts the amplitude and anisotropy of the stochastic gravitational wave background from compact binary mergers using Euclid galaxy data, and compares it with semi-analytical models to develop a framework for future astrophysical inference.

Contribution

It introduces a novel method to forecast SGWB anisotropies based on galaxy simulations and Bayesian inference, linking gravitational wave data with galaxy surveys.

Findings

Predicted SGWB frequency spectrum and anisotropy from galaxy catalog data.

Identified key parameters influencing SGWB models.

Developed a Bayesian framework for parameter inference in SGWB predictions.

Abstract

We estimate the amplitude and spatial anisotropy in the stochastic gravitational wave background (SGWB) energy density due to compact binary coalescence (CBC) events: binary black holes (BBH), binary neutron stars (BNS), and black hole-neutron star (BHNS) mergers. Our starting point is the Flagship Simulation Galaxy Catalogue developed by the Euclid Consortium. For each galaxy in the Catalogue, we use the simulated mass and starformation to constrain the galaxy's star-formation history, and predict its contribution to the gravitational-wave energy density through CBC mergers. Combining such contributions from all galaxies in the Catalogue results in a prediction for the frequency spectrum and spatial anisotropy of the CBC SGWB. We also compare this prediction to semi-analytical models of SGWB generated by compact binaries. We identify a set of effective parameters that capture the key features of these models, and we apply a Bayesian framework to infer these parameters assuming an ideal scenario of cosmic variance-limited search. This represents the first step toward developing a comprehensive framework that will eventually enable the correlation of SGWB anisotropy and \textit{Euclid} galaxy data, potentially allowing us to extract valuable astrophysical information from this new observable.