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What does strong gravitational lensing? The mass and redshift distribution of high-magnification lenses.

Robertson, Andrew and Smith, Graham P. and Massey, Richard and Eke, Vincent and Jauzac, Mathilde and Bianconi, Matteo and Ryczanowski, Dan (2020) 'What does strong gravitational lensing? The mass and redshift distribution of high-magnification lenses.', Monthly notices of the Royal Astronomical Society., 495 (4). pp. 3727-3739.


Many distant objects can only be detected, or become more scientifically valuable, if they have been highly magnified by strong gravitational lensing. We use eagle and bahamas, two recent cosmological hydrodynamical simulations, to predict the probability distribution for both the lens mass and lens redshift when point sources are highly magnified by gravitational lensing. For sources at a redshift of two, we find the distribution of lens redshifts to be broad, peaking at z ≈ 0.6. The contribution of different lens masses is also fairly broad, with most high-magnification lensing due to lenses with halo masses between 1012 and 1014 M⊙. Lower mass haloes are inefficient lenses, while more massive haloes are rare. We find that a simple model in which all haloes have singular isothermal sphere density profiles can approximately reproduce the simulation predictions, although such a model over-predicts the importance of haloes with mass <1012 M⊙ for lensing. We also calculate the probability that point sources at different redshifts are strongly lensed. At low redshift, high magnifications are extremely unlikely. Each z = 0.5 source produces, on average, 5 ± 107 images with magnification greater than ten; for z = 2 this increases to about 2 ± 105. Our results imply that searches for strongly lensed optical transients, including the optical counterparts to strongly lensed gravitational waves, can be optimized by monitoring massive galaxies, groups and clusters rather than concentrating on an individual population of lenses.

Item Type:Article
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Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2020 The Author(s) . Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:19 May 2020
Date deposited:26 May 2020
Date of first online publication:23 May 2020
Date first made open access:09 June 2020

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