Predictions for LISA and PTA based on SHARK galaxy simulations

TL;DR

This paper analyzes gravitational wave signals from massive black hole mergers using SHARK galaxy simulations, predicting detection rates for LISA and PTAs, and exploring the impact of different galaxy evolution models.

Contribution

It introduces a comprehensive analysis of MBH merger predictions across multiple galaxy evolution models within the SHARK framework, assessing GW detectability with upcoming observatories.

Findings

LISA could detect several to tens of MBH merger events annually.

Detection rates vary significantly with seed formation scenarios and growth models.

The GW background amplitude at nHz frequencies is estimated between 1.4×10^{-16} and 1.1×10^{-15}.

Abstract

We present our analysis of a set of populations of massive black hole (MBH) binaries generated in the recent semi-analytic model of galaxy evolution (SHARK). We focus on studying gravitational wave (GW) emission produced during MBH mergers in terms of their detectability with current and future detectors, namely, Pulsar Timing Arrays (PTAs) and Laser Interferometer Space Antenna (LISA). The key advantage of SHARK is that it provides a way to explore a number of distinct models of MBH and galaxy evolution processes within a consistent framework and it was also successfully tested against current constraints from electromagnetic observations. In our work, we studied 12 models that vary in terms of their MBH seed formation scenarios and we tested two different MBH growth and feedback models. Based on our estimates, we find that LISA will be able to detect several to several tens of merger events per year for the most and least massive seed scenarios, respectively. We also show that the strength of this relation depends on the MBH growth model, where in the most extreme case, we find twice as many detected events for the same initial seed masses. Finally, we estimated the amplitude of the GW background at nHz frequencies to be on the order of $1.4\cdot10^{-16} - 1.1\cdot10^{-15}$. This value depends solely on the time delay between the merger of galaxies and their MBHs.