Intensity and anisotropies of the stochastic Gravitational Wave background from merging compact binaries in galaxies

TL;DR

This paper models the isotropic and anisotropic components of the stochastic gravitational wave background from merging compact binaries in galaxies, predicting their observable signatures and analyzing their spectral and angular properties.

Contribution

It introduces an empirical galactic astrophysics approach to predict SGWB anisotropies and their angular power spectrum, including detailed source contributions and detector sensitivities.

Findings

SGWB anisotropy power spectrum follows a power law on large scales

Spectral shape varies among source types and detector sensitivities

Simulated high-resolution sky maps incorporate Poisson and clustering effects

Abstract

We investigate the isotropic and anisotropic components of the Stochastic Gravitational Wave Background (SGWB) originated from unresolved merging compact binaries in galaxies. We base our analysis on an empirical approach to galactic astrophysics that allows to follow the evolution of individual systems. We then characterize the energy density of the SGWB as a tracer of the total matter density, in order to compute the angular power spectrum of anisotropies with the Cosmic Linear Anisotropy Solving System (CLASS) public code in full generality. We obtain predictions for the isotropic energy density and for the angular power spectrum of the SGWB anisotropies, and study the prospect for their observations with advanced Laser Interferometer Gravitational-Wave and Virgo Observatories and with the Einstein Telescope. We identify the contributions coming from different type of sources (binary black holes, binary neutron stars and black hole-neutron star) and from different redshifts. We examine in detail the spectral shape of the energy density for all types of sources, comparing the results for the two detectors. We find that the power spectrum of the SGWB anisotropies behaves like a power law on large angular scales and drops at small scales: we explain this behaviour in terms of the redshift distribution of sources that contribute most to the signal, and of the sensitivities of the two detectors. Finally, we simulate a high resolution full sky map of the SGWB starting from the power spectra obtained with CLASS and including Poisson statistics and clustering properties.