Finding the One: Identifying the Host Galaxies of Gravitational-Wave Sources

TL;DR

This paper analyzes how ground-based gravitational-wave detectors can localize binary merger sources, predicting that future networks will identify host galaxies for a few nearby, loud events, enabling astrophysical and cosmological studies.

Contribution

The study provides detailed simulations of localization capabilities, demonstrating the potential to identify host galaxies for a small number of well-localized gravitational-wave events.

Findings

Existence of a tail of well-localized events with <10 deg^2 sky area.

Potential to localize sources within <1000 Mpc^3 volume.

Future networks may identify host galaxies for a few nearby events annually.

Abstract

We explore the localization of compact binary coalescences with ground-based gravitational-wave detector networks. We simulate tens of thousands of binary events, and present the distributions of localization sky areas and localization volumes for a range of sources and network configurations. We show that generically there exists a tail of particularly well-localized events, with 2D and 3D localizations of $<10\,\mbox{deg}^2$ and $<1000\,\mbox{Mpc}^3$ achievable, respectively, starting in LIGO/Virgo's third observing run. Incorporating estimates for the galaxy density and the binary event rates, we argue that future gravitational-wave detector networks will localize a small number of binary systems per year to a sufficiently small volume that the unique host galaxy might be identified. For these golden events, which are generally the closest and loudest ones, the gravitational-wave detector networks will point (in 3D; the length of the finger matters) directly at the source. This will allow for studies of the properties of the host galaxies of compact binary mergers, which may be an important component in exploring the formation channels of these sources. In addition, since the host will provide an independent measurement of the redshift, this will allow the use of the event as a standard siren to measure cosmology. Furthermore, identification of a small number of host galaxies can enable deep follow-up searches for associated electromagnetic transients.