References of "Van de Vyvere, Lyne"
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See detaillenstronomy II: A gravitational lensing softwareecosystem
Birrer, Simon; Shajib, Anowar J.; Gilman, Daniel et al

in Journal of Open Source Software (2021)

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See detailTime delay lens modelling challenge
Ding, X.; Treu, T.; Birrer, S. et al

in Monthly Notices of the Royal Astronomical Society (2021), 503

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 H[SUB]0[/SUB]. However, published state-of-the ... [more ▼]

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 H[SUB]0[/SUB]. However, published state-of-the-art 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 H[SUB]0[/SUB] 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 post-unblinding analysis of Rung 3 showed the numerical precision of the ray-traced cosmological simulations to be insufficient to test lens modelling methodology at the percent level, making the results difficult to interpret. A new challenge with improved simulations is needed to make further progress in the investigation of systematic uncertainties. For completeness, we present the Rung 3 results in an appendix and use them to discuss various approaches to mitigating against similar subtle data generation effects in future blind challenges. [less ▲]

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See detailThe impact of mass map truncation on strong lensing simulations
Van de Vyvere, Lyne ULiege; Sluse, Dominique ULiege; Mukherjee, Sampath ULiege et al

in Astronomy and Astrophysics (2020), 644

Strong gravitational lensing is a powerful tool to measure cosmological parameters and to study galaxy evolution mechanisms. However, quantitative strong lensing studies often require mock observations ... [more ▼]

Strong gravitational lensing is a powerful tool to measure cosmological parameters and to study galaxy evolution mechanisms. However, quantitative strong lensing studies often require mock observations. To capture the full complexity of galaxies, the lensing galaxy is often drawn from high resolution, dark matter only or hydro-dynamical simulations. These have their own limitations, but the way we use them to emulate mock lensed systems may also introduce significant artefacts. In this work we identify and explore the specific impact of mass truncation on simulations of strong lenses by applying different truncation schemes to a fiducial density profile with conformal isodensity contours. Our main finding is that improper mass truncation can introduce undesired artificial shear. The amplitude of the spurious shear depends on the shape and size of the truncation area as well as on the slope and ellipticity of the lens density profile. Due to this effect, the value of H0 or the shear amplitude inferred by modelling those systems may be biased by several percents. However, we show that the effect becomes negligible provided that the lens projected map extends over at least 50 times the Einstein radius. [less ▲]

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See detailTDCOSMO. IV. Hierarchical time-delay cosmography - joint inference of the Hubble constant and galaxy density profiles
Birrer, S.; Shajib, A. J.; Galan, A. et al

in Astronomy and Astrophysics (2020), 643

The H0LiCOW collaboration inferred via strong gravitational lensing time delays a Hubble constant value of H[SUB]0[/SUB] = 73.3[SUB]-1.8[/SUB][SUP]+1.7[/SUP] km s[SUP]-1[/SUP] Mpc[SUP]-1[/SUP], describing ... [more ▼]

The H0LiCOW collaboration inferred via strong gravitational lensing time delays a Hubble constant value of H[SUB]0[/SUB] = 73.3[SUB]-1.8[/SUB][SUP]+1.7[/SUP] km s[SUP]-1[/SUP] Mpc[SUP]-1[/SUP], describing deflector mass density profiles by either a power-law or stars (constant mass-to-light ratio) plus standard dark matter halos. The mass-sheet transform (MST) that leaves the lensing observables unchanged is considered the dominant source of residual uncertainty in H[SUB]0[/SUB]. We quantify any potential effect of the MST with a flexible family of mass models, which directly encodes it, and they are hence maximally degenerate with H[SUB]0[/SUB]. Our calculation is based on a new hierarchical Bayesian approach in which the MST is only constrained by stellar kinematics. The approach is validated on mock lenses, which are generated from hydrodynamic simulations. We first applied the inference to the TDCOSMO sample of seven lenses, six of which are from H0LiCOW, and measured H[SUB]0[/SUB] = 74.5[SUB]-6.1[/SUB][SUP]+5.6[/SUP] km s[SUP]-1[/SUP] Mpc[SUP]-1[/SUP]. Secondly, in order to further constrain the deflector mass density profiles, we added imaging and spectroscopy for a set of 33 strong gravitational lenses from the Sloan Lens ACS (SLACS) sample. For nine of the 33 SLAC lenses, we used resolved kinematics to constrain the stellar anisotropy. From the joint hierarchical analysis of the TDCOSMO+SLACS sample, we measured H[SUB]0[/SUB] = 67.4[SUB]-3.2[/SUB][SUP]+4.1[/SUP] km s[SUP]-1[/SUP] Mpc[SUP]-1[/SUP]. This measurement assumes that the TDCOSMO and SLACS galaxies are drawn from the same parent population. The blind H0LiCOW, TDCOSMO-only and TDCOSMO+SLACS analyses are in mutual statistical agreement. The TDCOSMO+SLACS analysis prefers marginally shallower mass profiles than H0LiCOW or TDCOSMO-only. Without relying on the form of the mass density profile used by H0LiCOW, we achieve a ∼5% measurement of H[SUB]0[/SUB]. While our new hierarchical analysis does not statistically invalidate the mass profile assumptions by H0LiCOW - and thus the H[SUB]0[/SUB] measurement relying on them - it demonstrates the importance of understanding the mass density profile of elliptical galaxies. The uncertainties on H[SUB]0[/SUB] derived in this paper can be reduced by physical or observational priors on the form of the mass profile, or by additional data. <P />The full analysis is available at <A href="https://github.com/TDCOSMO/hierarchy_analysis_2020_public">http://https://github.com/TDCOSMO/hierarchy_analysis_2020_public</A>. [less ▲]

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See detailTDCOSMO. I. An exploration of systematic uncertainties in the inference of H[SUB]0[/SUB] from time-delay cosmography
Millon, M.; Galan, A.; Courbin, F. et al

in Astronomy and Astrophysics (2020), 639

Time-delay cosmography of lensed quasars has achieved 2.4% precision on the measurement of the Hubble constant, H[SUB]0[/SUB]. As part of an ongoing effort to uncover and control systematic uncertainties ... [more ▼]

Time-delay cosmography of lensed quasars has achieved 2.4% precision on the measurement of the Hubble constant, H[SUB]0[/SUB]. As part of an ongoing effort to uncover and control systematic uncertainties, we investigate three potential sources: 1- stellar kinematics, 2- line-of- sight 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[SUB]0[/SUB] from the seven lenses analyzed by TDCOSMO. Second, we find no bias to arise from incorrect estimation of the line-of-sight effects. Third, we show that elliptical composite (stars + dark matter halo), power-law, and cored power-law mass profiles have the flexibility to yield a broad range in H[SUB]0[/SUB] values. However, the TDCOSMO procedures that model the data with both composite and power-law mass profiles are informative. If the models agree, as we observe in real systems owing to the "bulge- halo" conspiracy, H[SUB]0[/SUB] 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[SUB]0[/SUB] = 74.0[SUB]-1.8[/SUB][SUP]+1.7[/SUP] km s[SUP]-1[/SUP] Mpc[SUP]-1[/SUP], while the power-law model yields 74.2[SUB]-1.6[/SUB][SUP]+1.6[/SUP] km s[SUP]-1[/SUP] Mpc[SUP]-1[/SUP]. In conclusion, we find no evidence of bias or errors larger than the current statistical uncertainties reported by TDCOSMO. [less ▲]

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