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

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 $\sim0.3\%$ of observed events will have been strongly lensed. We predict detections of $\sim 2$ lensing pairs per year with A+, and $\sim 200$ pairs 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 also 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 $\sim12\%$ after 5 years. Finally, we show that both the presence or absence of strong lensing 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.