Timedelay cosmography of lensed quasars has achieved 2.4% precision on the measurement of the Hubble constant, H 0 . As part of an ongoing effort to uncover and control systematic uncertainties, we investigate three potential sources: 1 stellar kinematics, 2 lineofsight effects, and 3 the deflector mass model. To meet this goal in a quantitative way, we reproduced the H0LiCOW/SHARP/STRIDES (hereafter TDCOSMO) procedures on a set of real and simulated data, and we find the following. First, stellar kinematics cannot be a dominant source of error or bias since we find that a systematic change of 10% of measured velocity dispersion leads to only a 0.7% shift on H 0 from the seven lenses analyzed by TDCOSMO. Second, we find no bias to arise from incorrect estimation of the lineofsight effects. Third, we show that elliptical composite (stars + dark matter halo), powerlaw, and cored powerlaw mass profiles have the flexibility to yield a broad range in H 0 values. However, the TDCOSMO procedures that model the data with both composite and powerlaw mass profiles are informative. If the models agree, as we observe in real systems owing to the “bulgehalo” conspiracy, H 0 is recovered precisely and accurately by both models. If the two models disagree, as in the case of some pathological models illustrated here, the TDCOSMO procedure either discriminates between them through the goodness of fit, or it accounts for the discrepancy in the final error bars provided by the analysis. This conclusion is consistent with a reanalysis of six of the TDCOSMO (real) lenses: the composite model yields H 0 = 74.0 −1.8 +1.7 km s −1 Mpc −1 , while the powerlaw model yields 74.2 −1.6 +1.6 km s −1 Mpc −1 . In conclusion, we find no evidence of bias or errors larger than the current statistical uncertainties reported by TDCOSMO.
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This content will become publicly available on May 1, 2024
TDCOSMO: XII. Improved Hubble constant measurement from lensing time delays using spatially resolved stellar kinematics of the lens galaxy
Stronglensing time delays enable the measurement of the Hubble constant ( H 0 ) independently of other traditional methods. The main limitation to the precision of timedelay cosmography is masssheet degeneracy (MSD). Some of the previous TDCOSMO analyses broke the MSD by making standard assumptions about the mass density profile of the lens galaxy, reaching 2% precision from seven lenses. However, this approach could potentially bias the H 0 measurement or underestimate the errors. For this work, we broke the MSD for the first time using spatially resolved kinematics of the lens galaxy in RXJ1131−1231 obtained from the Keck Cosmic Web Imager spectroscopy, in combination with previously published time delay and lens models derived from Hubble Space Telescope imaging. This approach allowed us to robustly estimate H 0 , effectively implementing a maximally flexible mass model. Following a blind analysis, we estimated the angular diameter distance to the lens galaxy D d = 865 −81 +85 Mpc and the timedelay distance D Δt = 2180 −271 +472 Mpc, giving H 0 = 77.1 −7.1 +7.3 km s −1 Mpc −1 – for a flat Λ cold dark matter cosmology. The error budget accounts for all uncertainties, including the MSD inherent to the lens mass profile and lineofsight effects, and those related to the mass–anisotropy degeneracy and projection effects. Our new measurement is in excellent agreement with those obtained in the past using standard simply parametrized mass profiles for this single system ( H 0 = 78.3 −3.3 +3.4 km s −1 Mpc −1 ) and for seven lenses ( H 0 = 74.2 −1.6 +1.6 km s −1 Mpc −1 ), or for seven lenses using singleaperture kinematics and the same maximally flexible models used by us ( H 0 = 73.3 −5.8 +5.8 km s −1 Mpc −1 ). This agreement corroborates the methodology of timedelay cosmography.
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 NSFPAR ID:
 10415544
 Date Published:
 Journal Name:
 Astronomy & Astrophysics
 Volume:
 673
 ISSN:
 00046361
 Page Range / eLocation ID:
 A9
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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