Abstract
We present a blind time-delay strong lensing (TDSL) cosmographic analysis of the doubly imaged quasar SDSS 1206+4332 . We combine the relative time delay between the quasar images, Hubble ...Space Telescope imaging, the Keck stellar velocity dispersion of the lensing galaxy, and wide-field photometric and spectroscopic data of the field to constrain two angular diameter distance relations. The combined analysis is performed by forward modelling the individual data sets through a Bayesian hierarchical framework, and it is kept blind until the very end to prevent experimenter bias. After unblinding, the inferred distances imply a Hubble constant H0 = 68.8$^{+5.4}_{-5.1}$ km s−1 Mpc−1, assuming a flat Λ cold dark matter cosmology with uniform prior on Ωm in 0.05, 0.5. The precision of our cosmographic measurement with the doubly imaged quasar SDSS 1206+4332 is comparable with those of quadruply imaged quasars and opens the path to perform on selected doubles the same analysis as anticipated for quads. Our analysis is based on a completely independent lensing code than our previous three H0LiCOW systems and the new measurement is fully consistent with those. We provide the analysis scripts paired with the publicly available software to facilitate independent analysis (footnote with link to www.h0licow.org). The consistency between blind measurements with independent codes provides an important sanity check on lens modelling systematics. By combining the likelihoods of the four systems under the same prior, we obtain H0 = 72.5$^{+2.1}_{-2.3}$ km s−1 Mpc−1. This measurement is independent of the distance ladder and other cosmological probes.
Gravitational microlensing is a powerful tool for probing the inner structure of strongly lensed quasars and for constraining parameters of the stellar mass function of lens galaxies. This is ...achieved by analysing microlensing light curves between the multiple images of strongly lensed quasars and accounting for the effects of three main variable components: (1) the continuum flux of the source, (2) microlensing by stars in the lens galaxy, and (3) reverberation of the continuum by the broad line region (BLR). The latter, ignored by state-of-the-art microlensing techniques, can introduce high-frequency variations which we show carry information on the BLR size. We present a new method that includes all these components simultaneously and fits the power spectrum of the data in the Fourier space rather than the observed light curve itself. In this new framework, we analyse COSMOGRAIL light curves of the two-image system QJ 0158-4325 known to display high-frequency variations. Using exclusively the low-frequency part of the power spectrum, our constraint on the accretion disk radius agrees with the thin-disk model estimate and the results of previous work where the microlensing light curves were fit in real space. However, if we also take into account the high-frequency variations, the data favour significantly smaller disk sizes than previous microlensing measurements. In this case, our results are only in agreement with the thin-disk model prediction only if we assume very low mean masses for the microlens population, i.e. ⟨
M
⟩ = 0.01
M
⊙
. At the same time, including the differentially microlensed continuum reverberation by the BLR successfully explains the high frequencies without requiring such low-mass microlenses. This allows us to measure, for the first time, the size of the BLR using single-band photometric monitoring; we obtain
R
BLR
= 1.6
−0.8
+1.5
× 10
17
cm, in good agreement with estimates using the BLR size–luminosity relation.
Context. The precise determination of the present-day expansion rate of the Universe, expressed through the Hubble constant H0, is one of the most pressing challenges in modern cosmology. Assuming ...flat ΛCDM, H0 inference at high redshift using cosmic microwave background data from Planck disagrees at the 4.4σ level with measurements based on the local distance ladder made up of parallaxes, Cepheids, and Type Ia supernovae (SNe Ia), often referred to as Hubble tension. Independent cosmological-model-insensitive ways to infer H0 are of critical importance. Aims. We apply an inverse distance ladder approach, combining strong-lensing time-delay distance measurements with SN Ia data. By themselves, SNe Ia are merely good indicators of relative distance, but by anchoring them to strong gravitational lenses we can obtain an H0 measurement that is relatively insensitive to other cosmological parameters. Methods. A cosmological parameter estimate was performed for different cosmological background models, both for strong-lensing data alone and for the combined lensing + SNe Ia data sets. Results. The cosmological-model dependence of strong-lensing H0 measurements is significantly mitigated through the inverse distance ladder. In combination with SN Ia data, the inferred H0 consistently lies around 73–74 km s−1 Mpc−1, regardless of the assumed cosmological background model. Our results agree closely with those from the local distance ladder, but there is a > 2σ tension with Planck results, and a ∼1.5σ discrepancy with results from an inverse distance ladder including Planck, baryon acoustic oscillations, and SNe Ia. Future strong-lensing distance measurements will reduce the uncertainties in H0 from our inverse distance ladder.
The upcoming Large Synoptic Survey Telescope (LSST) will detect many strongly lensed Type Ia supernovae (LSNe Ia) for time-delay cosmography. This will provide an independent and direct way for ...measuring the Hubble constant H0, which is necessary to address the current 4.4σ tension in H0 between the local distance ladder and the early Universe measurements. We present a detailed analysis of different observing strategies (also referred to as cadence strategy) for the LSST, and quantify their impact on time-delay measurement between multiple images of LSNe Ia. For this, we simulated observations by using mock LSNe Ia for which we produced mock-LSST light curves that account for microlensing. Furthermore, we used the free-knot splines estimator from the software PyCS to measure the time delay from the simulated observations. We find that using only LSST data for time-delay cosmography is not ideal. Instead, we advocate using LSST as a discovery machine for LSNe Ia, enabling time delay measurements from follow-up observations from other instruments in order to increase the number of systems by a factor of 2–16 depending on the observing strategy. Furthermore, we find that LSST observing strategies, which provide a good sampling frequency (the mean inter-night gap is around two days) and high cumulative season length (ten seasons with a season length of around 170 days per season), are favored. Rolling cadences subdivide the survey and focus on different parts in different years; these observing strategies trade the number of seasons for better sampling frequency. In our investigation, this leads to half the number of systems in comparison to the best observing strategy. Therefore rolling cadences are disfavored because the gain from the increased sampling frequency cannot compensate for the shortened cumulative season length. We anticipate that the sample of lensed SNe Ia from our preferred LSST cadence strategies with rapid follow-up observations would yield an independent percent-level constraint on H0.
We present a new measurement of the Hubble Constant H sub( 0) and other cosmological parameters based on the joint analysis of three multiply imaged quasar systems with measured gravitational time ...delays. First, we measure the time delay of HE 0435-1223 from 13-yr light curves obtained as part of the COSMOGRAIL project. Companion papers detail the modelling of the main deflectors and line-of-sight effects, and how these data are combined to determine the time-delay distance of HE 0435-1223. Crucially, the measurements are carried out blindly with respect to cosmological parameters in order to avoid confirmation bias. We then combine the time-delay distance of HE 0435-1223 with previous measurements from systems B1608+656 and RXJ1131-1231 to create a Time Delay Strong Lensing probe (TDSL). In flat Lambda cold dark matter ( Lambda CDM) with free matter and energy density, we find H sub( 0) =71.9... km s super( -1) Mpc super( -1) and Omega sub( Lambda )=0.62... This measurement is completely independent of, and in agreement with, the local distance ladder measurements of H sub( 0). We explore more general cosmological models combining TDSL with other probes, illustrating its power to break degeneracies inherent to other methods. The joint constraints from TDSL and Planck are H sub( 0) = 69.2... km s super( -1) Mpc super( -1) , Omega sub( Lambda )=0.70... and Omega sub( k)=0.003+0.004-0.006 in open ...CDM and H sub( 0) =79.0... km s super( -1) Mpc super( -1), Omega sub( de)=0.77... and w=-1.38... in flat wCDM. In combination with Planck and baryon acoustic oscillation data, when relaxing the constraints on the numbers of relativistic species we find N sub( eff) = 3.34... in N sub( eff) Lambda CDM and when relaxing the total mass of neutrinos we find ...m sub( ...) less than or equal to ...0.182 eV in m sub( nu )...CDM. Finally, in an open wCDM in combination with Planck and cosmic microwave background lensing, we find H sub( 0) =77.9... km s super( -1) Mpc super( -1), Omega sub( de) = 0.77..., Omega sub( k) = -0.003... and w=-1.37... (ProQuest: ... denotes formulae/symbols omitted.)
It has recently been proposed that gravitationally lensed type-Ia supernovae can provide microlensing-free time-delay measurements provided that the measurement is taken during the achromatic ...expansion phase of the explosion and that color light curves are used rather than single-band light curves. If verified, this would provide both precise and accurate time-delay measurements, making lensed type-Ia supernovae a new golden standard for time-delay cosmography. However, the 3D geometry of the expanding shell can introduce an additional bias that has not yet been fully explored. In this work, we present and discuss the impact of this effect on time-delay cosmography with lensed supernovae and find that on average it leads to a bias of a few tenths of a day for individual lensed systems. This is negligible in view of the cosmological time delays predicted for typical lensed type-Ia supernovae but not for the specific case of the recently discovered type-Ia supernova iPTF16geu, whose time delays are expected to be smaller than a day.
COSMOGRAIL is a long-term photometric monitoring of gravitationally lensed quasars aimed at implementing Refsdal's time-delay method to measure cosmological parameters, in particular H sub(0). Given ...the long and well sampled light curves of strongly lensed quasars, time-delay measurements require numerical techniques whose quality must be assessed. To this end, and also in view of future monitoring programs or surveys such as the LSST, a blind signal processing competition named Time Delay Challenge 1 (TDC1) was held in 2014. The aim of the present paper, which is based on the simulated light curves from the TDC1, is double. First, we test the performance of the time-delay measurement techniques currently used in COSMOGRAIL. Second, we analyse the quantity and quality of the harvest of time delays obtained from the TDC1 simulations. To achieve these goals, we first discover time delays through a careful inspection of the light curves via a dedicated visual interface. Our measurement algorithms can then be applied to the data in an automated way. We show that our techniques have no significant biases, and yield adequate uncertainty estimates resulting in reduced chi super(2) values between 0.5 and 1.0. We provide estimates for the number and precision of time-delay measurements that can be expected from future time-delay monitoring campaigns as a function of the photometric signal-to-noise ratio and of the true time delay. We make our blind measurements on the TDC1 data publicly available.
Abstract
Galaxies located in the environment or along the line of sight towards gravitational lenses can significantly affect lensing observables, and can lead to systematic errors on the measurement ...of H
0 from the time-delay technique. We present the results of a systematic spectroscopic identification of the galaxies in the field of view of the lensed quasar HE 0435−1223 using the W. M. Keck, Gemini and ESO-Very Large telescopes. Our new catalogue triples the number of known galaxy redshifts in the direct vicinity of the lens, expanding to 102 the number of measured redshifts for galaxies separated by less than 3 arcmin from the lens. We complement our catalogue with literature data to gather redshifts up to 15 arcmin from the lens, and search for galaxy groups or clusters projected towards HE 0435−1223. We confirm that the lens is a member of a small group that includes at least 12 galaxies, and find 8 other group candidates near the line of sight of the lens. The flexion shift, namely the shift of lensed images produced by high-order perturbation of the lens potential, is calculated for each galaxy/group and used to identify which objects produce the largest perturbation of the lens potential. This analysis demonstrates that (i) at most three of the five brightest galaxies projected within 12 arcsec of the lens need to be explicitly used in the lens models, and (ii) the groups can be treated in the lens model as an external tidal field (shear) contribution.
With the advent of high-cadence and multi-band photometric monitoring facilities, continuum reverberation mapping is becoming of increasing importance for the measurement of the physical size of ...quasar accretion disks. The method is based on measuring the time it takes for a signal to propagate from the center to the outer parts of the central engine, assuming the continuum light curve at a given wavelength has a time shift of the order of a few days with respect to light curves obtained at shorter wavelengths. We show that with high-quality light curves, this assumption is no longer valid and that light curves at different wavelengths are not only shifted in time, but also distorted: in the context of the lamp-post model and thin-disk geometry, the multi-band light curves are, in fact, convolved by a transfer function whose size increases with wavelength. We illustrate the effect with simulated light curves in the Large Synoptic Survey Telescope (LSST) ugrizy bands and examine the impact on the delay measurements when using three different methods, namely
JAVELIN
,
CREAM
, and
PyCS
. We find that current accretion disk sizes estimated from
JAVELIN
and
PyCS
are underestimated by ∼30% and that unbiased measurements are only obtained with methods that properly take the skewed transfer functions into account, as the
CREAM
code does. With the LSST-like light curves, we expect to achieve measurement errors below 5% with a typical two-day photometric cadence.
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