An estimate of the gravitational-wave background from the observed cosmological distribution of quasars

TL;DR

This paper estimates the gravitational-wave background generated by the cosmological distribution of quasars, using SDSS data to model black hole mergers and assess detectability by LISA.

Contribution

It provides a novel estimate of the gravitational-wave background from quasars based on SDSS data and black hole mass modeling, assessing its potential detectability.

Findings

The gravitational-wave background from quasars is likely only marginally detectable by LISA.

The black hole mass distribution in quasars follows a log-normal pattern with a mean around 2×10^8 solar masses.

Detection prospects depend on the completeness of quasar catalogs.

Abstract

We study the gravitational-wave background from the observed cosmological quasar distribution. Using the DR9Q quasar catalogue from the ninth data release of the Sloan Digital Sky Survey (SDSS), we create a complete, statistically consistent sample of quasars from $z=0.3$ to $5.4$. Employing the spectroscopic information from the catalogue we estimate the masses of the supermassive black holes hosted by the quasars in the sample, resulting in a log-normal distribution of mean $10^{8.32\pm0.33}M_{\odot}$. The computation of the individual gravitational-wave strains relies on specific functional forms derived from simulations of gravitational collapse and mergers of massive black hole binaries. The background gravitational-wave emission is assembled by adding up the individual signals from each quasar modelled as plane waves whose interference can be constructive or destructive depending on the quasar evolutionary state. Our results indicate that the estimated gravitational-wave background discussed in this work could only be marginally detectable by LISA. This conclusion might change if more complete quasar catalogs than that provided by the SDSS were available.