Kavli Affiliate: Daniel Holz
| First 5 Authors: Amanda Farah, Amanda Farah, , ,
| Summary:
All gravitational-wave signals are inevitably gravitationally lensed by
intervening matter as they propagate through the Universe. When a
gravitational-wave signal is magnified, it appears to have originated from a
closer, more massive system. Thus, high-mass outliers to the gravitational-wave
source population are often proposed as natural candidates for strongly lensed
events. However, when using a data-driven method for identifying population
outliers, we find that high-mass outliers are not necessarily strongly lensed,
nor will the majority of strongly-lensed signals appear as high-mass outliers.
This is both because statistical fluctuations produce a larger effect on
observed binary parameters than does lensing magnification, and because
lensing-induced outliers must originate from intrinsically high-mass sources,
which are rare. Thus, the appearance of a single lensing-induced outlier
implies the existence of many other lensed events within the catalog. We
additionally show that it is possible to constrain the strong lensing optical
depth, which is a fundamental quantity of our Universe, with the detection or
absence of high-mass outliers. However, constraints using the latest
gravitational-wave catalog are weak$unicodex2014$we obtain an upper limit on
the optical depth of sources at redshift $1$ magnified by a factor of $5$ or
more of $tau(mugeq5,z=1)leq 0.035 unicodex2014$and future observing runs
will not make an outlier-based method competitive with other probes of the
optical depth. Future work will investigate the ability of the full inferred
population of compact binaries to inform the distribution of lenses in the
Universe, opening a unique opportunity to access the high-redshift Universe and
constrain cosmic structures.
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