Please repeat: Strong lensing of gravitational waves as a probe of compact binary and galaxy populations

TL;DR

This paper investigates how strong gravitational lensing of gravitational waves can be used to study galaxy and binary source populations, predicting detection rates and how lensing observations constrain galaxy properties and formation models.

Contribution

It provides detailed calculations of lensing event rates for current and future detectors, and demonstrates how lensing observations can constrain galaxy velocity dispersions and source population characteristics.

Findings

Approximately 0.1% of 3G gravitational wave events are strongly lensed.

Predicted detection of about 1 lensing pair per year with A+ and 50 with ET/CE.

Lensing observations can constrain galaxy velocity dispersion to about 21% after 5 years.

Abstract

Strong gravitational lensing of gravitational wave sources offers a novel probe of both the lens galaxy and the binary source population. In particular, the strong lensing event rate and the time delay distribution of multiply-imaged gravitational-wave binary coalescence events can be used to constrain the mass distribution of the lenses as well as the intrinsic properties of the source population. We calculate the strong lensing event rate for a range of second (2G) and third generation (3G) detectors, including Advanced LIGO/Virgo, A+, Einstein Telescope (ET), and Cosmic Explorer (CE). For 3G detectors, we find that {$\sim0.1\%$} of observed events are expected to be strongly lensed. We predict detections of {$\sim 1$} lensing pair per year with A+, and {$\sim 50$} pairs {per year} with ET/CE. These rates are highly sensitive to the characteristic galaxy velocity dispersion, $\sigma_*$, implying that observations of the rates will be a sensitive probe of lens properties. We explore using the time delay distribution between multiply-imaged gravitational-wave sources to constrain properties of the lenses. We find that 3G detectors would constrain $\sigma_*$ to {$\sim21\%$ after 5 years}. Finally, we show that the presence or absence of strong lensing {within the detected population} provides useful insights into the source redshift and mass distribution out to redshifts beyond the peak of the star formation rate, which can be used to constrain formation channels and their relation to the star formation rate and delay time distributions for these systems.