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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 amore »

ABSTRACT The magnifications of compactsource lenses are extremely sensitive to the presence of lowmass dark matter haloes along the entire sightline from the source to the observer. Traditionally, the study of dark matter structure in compactsource strong gravitational lenses has been limited to radioloud systems, as the radio emission is extended and thus unaffected by microlensing which can mimic the signal of dark matter structure. An alternate approach is to measure quasar nuclearnarrowline emission, which is free from microlensing and present in virtually all quasar lenses. In this paper, we double the number of systems which can be used for gravitational lensing analyses by presenting measurements of narrowline emission from a sample of eight quadruply imaged quasar lens systems, WGD J0405−3308, HS 0810+2554, RX J0911+0551, SDSS J1330+1810, PS J1606−2333, WFI 2026−4536, WFI 2033−4723, and WGD J2038−4008. We describe our updated grism spectral modelling pipeline, which we use to measure narrowline fluxes with uncertainties of 2–10 per cent, presented here. We fit the lensed image positions with smooth mass models and demonstrate that these models fail to produce the observed distribution of image fluxes over the entire sample of lenses. Furthermore, typical deviations are larger than those expected from macromodel uncertainties. This discrepancymore »

ABSTRACT In recent years, breakthroughs in methods and data have enabled gravitational time delays to emerge as a very powerful tool to measure the Hubble constant H0. However, published stateoftheart analyses require of order 1 yr of expert investigator time and up to a million hours of computing time per system. Furthermore, as precision improves, it is crucial to identify and mitigate systematic uncertainties. With this time delay lens modelling challenge, we aim to assess the level of precision and accuracy of the modelling techniques that are currently fast enough to handle of order 50 lenses, via the blind analysis of simulated data sets. The results in Rungs 1 and 2 show that methods that use only the point source positions tend to have lower precision ($10\!\!20{{\ \rm per\ cent}}$) while remaining accurate. In Rung 2, the methods that exploit the full information of the imaging and kinematic data sets can recover H0 within the target accuracy (A < 2 per cent) and precision (<6 per cent per system), even in the presence of a poorly known point spread function and complex source morphology. A postunblinding analysis of Rung 3 showed the numerical precision of the raytraced cosmological simulations to be insufficient to test lensmore »

We present six new timedelay measurements obtained from R c band monitoring data acquired at the Max Planck Institute for Astrophysics (MPIA) 2.2 m telescope at La Silla observatory between October 2016 and February 2020. The lensed quasars HE 0047−1756, WG 0214−2105, DES 0407−5006, 2M 1134−2103, PSJ 1606−2333, and DES 2325−5229 were observed almost daily at high signaltonoise ratio to obtain highquality light curves where we can record fast and smallamplitude variations of the quasars. We measured time delays between all pairs of multiple images with only one or two seasons of monitoring with the exception of the time delays relative to image D of PSJ 1606−2333. The most precise estimate was obtained for the delay between image A and image B of DES 0407−5006, where τ AB = −128.4 −3.8 +3.5 d (2.8% precision) including systematics due to extrinsic variability in the light curves. For HE 0047−1756, we combined our highcadence data with measurements from decadelong light curves from previous COSMOGRAIL campaigns, and reach a precision of 0.9 d on the final measurement. The present work demonstrates the feasibility of measuring time delays in lensed quasars in only one or two seasons, provided high signaltonoise ratio data are obtainedmore »

We present new measurements of the time delays of WFI2033−4723. The data sets used in this work include 14 years of data taken at the 1.2 m Leonhard Euler Swiss telescope, 13 years of data from the SMARTS 1.3 m telescope at Las Campanas Observatory and a single year of highcadence and highprecision monitoring at the MPIA 2.2 m telescope. The time delays measured from these different data sets, all taken in the R band, are in good agreement with each other and with previous measurements from the literature. Combining all the timedelay estimates from our data sets results in Δ t AB = 36.2 +0.7 −0.8 days (2.1% precision), Δ t AC = −23.3 +1.2 −1.4 days (5.6%) and Δ t BC = −59.4 +1.3 −1.3 days (2.2%). In addition, the close image pair A1A2 of the lensed quasars can be resolved in the MPIA 2.2 m data. We measure a time delay consistent with zero in this pair of images. We also explore the prior distributions of microlensing timedelay potentially affecting the cosmological timedelay measurements of WFI2033−4723. Our timedelay measurements are not precise enough to conclude that microlensing time delay is present or absent from the data. Thismore »

ABSTRACT We present a blind timedelay cosmographic analysis for the lens system DES J0408−5354. This system is extraordinary for the presence of two sets of multiple images at different redshifts, which provide the opportunity to obtain more information at the cost of increased modelling complexity with respect to previously analysed systems. We perform detailed modelling of the mass distribution for this lens system using three band Hubble Space Telescope imaging. We combine the measured time delays, lineofsight central velocity dispersion of the deflector, and statistically constrained external convergence with our lens models to estimate two cosmological distances. We measure the ‘effective’ timedelay distance corresponding to the redshifts of the deflector and the lensed quasar $D_{\Delta t}^{\rm eff}=$$3382_{115}^{+146}$ Mpc and the angular diameter distance to the deflector Dd = $1711_{280}^{+376}$ Mpc, with covariance between the two distances. From these constraints on the cosmological distances, we infer the Hubble constant H0= $74.2_{3.0}^{+2.7}$ km s−1 Mpc−1 assuming a flat ΛCDM cosmology and a uniform prior for Ωm as $\Omega _{\rm m} \sim \mathcal {U}(0.05, 0.5)$. This measurement gives the most precise constraint on H0 to date from a single lens. Our measurement is consistent with that obtained from the previous sample of six lenses analysed by the H0more »