Consequences of the lack of azimuthal freedom in the modeling of lensing galaxies

Abstract

Massive elliptical galaxies can display structures that deviate from a pure elliptical shape, such as a twist of the principal axis or variations in the axis ratio with galactocentric distance. Although satisfactory lens modeling is generally achieved without accounting for these azimuthal structures, the question about their impact on inferred lens parameters remains, in particular, on time delays as they are used in time-delay cosmography. This paper aims at characterizing these effects and quantifying their impact considering realistic amplitudes of the variations. We achieved this goal by creating mock lensing galaxies with morphologies based on two data sets: observational data of local elliptical galaxies, and hydrodynamical simulations of elliptical galaxies at a typical lens redshift. We then simulated images of the lensing systems with space-based data quality and modeled them in a standard way to assess the impact of a lack of azimuthal freedom in the lens model. We find that twists in lensing galaxies are easily absorbed in homoeidal lens models by a change in orientation of the lens up to 10° with respect to the reference orientation at the Einstein radius, and of the shear by up to 20° with respect to the input shear orientation. The ellipticity gradients, on the other hand, can introduce a substantial amount of shear that may impact the radial mass model and consequently bias $H_0$, up to 10 km/s/Mpc. However, we find that light is a good tracer of azimuthal structures, meaning that direct imaging should be capable of diagnosing their presence. This in turn implies that such a large bias is unlikely to be unaccounted for in standard modeling practices. Furthermore, the overall impact of twists and ellipticity gradients averages out at a population level. For the galaxy populations we considered, the cosmological inference remains unbiased.

Accepted for publication in A&A, 19 pages

References in corpus (22)

• The NumPy array: a structure for efficient numerical computation
• The EAGLE project: Simulating the evolution and assembly of galaxies and their environments
• Introducing the Illustris Project: Simulating the coevolution of dark and visible matter in the Universe
• Large Magellanic Cloud Cepheid Standards Provide a 1% Foundation for the Determination of the Hubble Constant and Stronger Evidence for Physics Beyond LambdaCDM
• The EAGLE simulations of galaxy formation: calibration of subgrid physics and model variations
• Baryon effects on the internal structure of LCDM halos in the EAGLE simulations
• The Megamaser Cosmology Project. XIII. Combined Hubble constant constraints
• H0LiCOW IV. Lens mass model of HE 0435-1223 and blind measurement of its time-delay distance for cosmology
• lenstronomy II: A gravitational lensing software ecosystem
• The Hubble Constant from Infrared Surface Brightness Fluctuation Distances
• Using The Baryonic Tully-Fisher Relation to Measure $H_o$
• Over-constrained Gravitational Lens Models and the Hubble Constant
• Isophotal Shapes of Elliptical/S0 Galaxies from the Sloan Digital Sky Survey
• AutoProf -- I. An automated non-parametric light profile pipeline for modern galaxy surveys
• TDCOSMO. VII. Boxyness/discyness in lensing galaxies : Detectability and impact on $H_0$
• Bayesian Analysis of Quasar Lightcurves with a Running Optimal Average: New Time Delay Measurements of COSMOGRAIL Gravitationally Lensed Quasars
• $R_{\mathrm{e}}$. I. Understanding galaxy sizes, associated luminosity densities, and the artificial division of the early-type galaxy population
• Large-Scale Gravitational Lens Modeling with Bayesian Neural Networks for Accurate and Precise Inference of the Hubble Constant
• Systematic errors induced by the elliptical power-law model in galaxy-galaxy strong lens modeling
• H0LiCOW XI. A weak lensing measurement of the external convergence in the field of the lensed quasar B1608+656 using HST and Subaru deep imaging
• Isophotal shapes of early-type galaxies to very faint levels
• The impact of mass map truncation on strong lensing simulations

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• TDCOSMO. XII. Improved Hubble constant measurement from lensing time delays using spatially resolved stellar kinematics of the lens galaxy
• TDCOSMO. IX. Systematic comparison between lens modelling software programs: time delay prediction for WGD 2038-4008
• Using wavelets to capture deviations from smoothness in galaxy-scale strong lenses
• Strong Lensing by Galaxies
• COOL-LAMPS III: Discovery of a 25".9 Separation Quasar Lensed by a Merging Galaxy Cluster