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Systematic Errors Induced by the Elliptical Power-law model in Galaxy–Galaxy Strong Lens Modeling

Cao, Xiaoyue and Li, Ran and Nightingale, J. W. and Massey, Richard and Robertson, Andrew and Frenk, Carlos S. and Amvrosiadis, Aristeidis and Amorisco, Nicola C. and He, Qiuhan and Etherington, Amy and Cole, Shaun and Zhu, Kai (2022) 'Systematic Errors Induced by the Elliptical Power-law model in Galaxy–Galaxy Strong Lens Modeling.', Research in Astronomy and Astrophysics, 22 (2). 025014.


The elliptical power-law (EPL) model of the mass in a galaxy is widely used in strong gravitational lensing analyses. However, the distribution of mass in real galaxies is more complex. We quantify the biases due to this model mismatch by simulating and then analysing mock Hubble Space Telescope imaging of lenses with mass distributions inferred from SDSS-MaNGA stellar dynamics data. We find accurate recovery of source galaxy morphology, except for a slight tendency to infer sources to be more compact than their true size. The Einstein radius of the lens is also robustly recovered with 0.1% accuracy, as is the global density slope, with 2.5% relative systematic error, compared to the 3.4% intrinsic dispersion. However, asymmetry in real lenses also leads to a spurious fitted ‘external shear’ with typical strength, γext = 0.015. Furthermore, time delays inferred from lens modelling without measurements of stellar dynamics are typically underestimated by ∼5%. Using such measurements from a sub-sample of 37 lenses would bias measurements of the Hubble constant H0 by ∼9%. Although this work is based on a particular set of MaNGA galaxies, and the specific value of the detected biases may change for another set of strong lenses, our results strongly suggest the next generation cosmography needs to use more complex lens mass models.

Item Type:Article
Full text:Publisher-imposed embargo until 27 October 2022.
(AM) Accepted Manuscript
File format - PDF
Publisher Web site:
Publisher statement:This is the Accepted Manuscript version of an article accepted for publication in Research in Astronomy and Astrophysics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at
Date accepted:27 October 2021
Date deposited:14 June 2022
Date of first online publication:02 February 2022
Date first made open access:27 October 2022

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