Time delay cosmography uses the arrival time delays between images in strong gravitational lenses to measure cosmological parameters, in particular the Hubble constant H0. The lens models used in time delay cosmography omit dark matter subhalos and lineofsight halos because their effects are assumed to be negligible. We explicitly quantify this assumption by analyzing realistic mock lens systems that include full populations of dark matter subhalos and lineofsight halos, applying the same modeling assumptions used in the literature to infer H0. We base the mock lenses on six quadruplyimaged quasars that have delivered measurements of the Hubble constant, and quantify the additional uncertainties and/or bias on a lensbylens basis. We show that omitting dark substructure does not bias inferences of H0. However, perturbations from substructure contribute an additional source of random uncertainty in the inferred value of H0 that scales as the square root of the lensing volume divided by the longest time delay. This additional source of uncertainty, for which we provide a fitting function, ranges from 0.6−2.4%. It may need to be incorporated in the error budget as the precision of cosmographic inferences from single lenses improves, and sets a precision limit on inferences from single lenses.
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TDCOSMO: III. Dark matter substructure meets dark energy. The effects of (sub)halos on stronglensing measurements of H 0
Time delay cosmography uses the arrival time delays between images in strong gravitational lenses to measure cosmological parameters, in particular the Hubble constant H 0 . The lens models used in time delay cosmography omit dark matter subhalos and lineofsight halos because their effects are assumed to be negligible. We explicitly quantify this assumption by analyzing mock lens systems that include full populations of dark matter subhalos and lineofsight halos, applying the same modeling assumptions used in the literature to infer H 0 . We base the mock lenses on six quadruply imaged quasars that have delivered measurements of the Hubble constant, and quantify the additional uncertainties and/or bias on a lensbylens basis. We show that omitting dark substructure does not bias inferences of H 0 . However, perturbations from substructure contribute an additional source of random uncertainty in the inferred value of H 0 that scales as the square root of the lensing volume divided by the longest time delay. This additional source of uncertainty, for which we provide a fitting function, ranges from 0.7 − 2.4%. It may need to be incorporated in the error budget as the precision of cosmographic inferences from single lenses improves, and it sets a precision limit on inferences from single lenses.
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 Award ID(s):
 1714953
 NSFPAR ID:
 10303237
 Date Published:
 Journal Name:
 Astronomy & Astrophysics
 Volume:
 642
 ISSN:
 00046361
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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