Skip to main content

Research Repository

Advanced Search

The “External” Shears In Strong Lens Models

Nightingale, James W.; Etherington, Amy; Massey, Richard

The “External” Shears In Strong Lens Models Thumbnail



The distribution of mass in galaxy-scale strong gravitational lenses is often modelled as an elliptical power law plus ‘external shear’, which notionally accounts for line-of-sight galaxies and cosmic shear. We argue that it does not, using three lines of evidence from the analysis of 54 galaxy-scale strong lenses: (i) strong lensing external shears do not correlate with weak lensing; (ii) the measured shear magnitudes in strong lenses (which are field galaxies) are too large (exceeding 0.05) for their environment and; (iii) the external shear position angle preferentially aligns or anti-aligns with the mass model position angle, indicating an internal origin. We argue the measured strong lensing shears are therefore systematically accounting for missing complexity in the canonical elliptical power-law mass model. If we can introduce this complexity into our lens models, this will further lensing studies of galaxy formation, dark matter and Cosmology.


Nightingale, J. W., Etherington, A., & Massey, R. (2022). The “External” Shears In Strong Lens Models. Proceedings of the International Astronomical Union, 18(S381), 13-16.

Journal Article Type Article
Acceptance Date Feb 2, 2024
Online Publication Date Mar 4, 2024
Publication Date 2022-12
Deposit Date Mar 11, 2024
Publicly Available Date Mar 11, 2024
Journal Proceedings of the International Astronomical Union
Print ISSN 1743-9213
Electronic ISSN 1743-9221
Publisher Cambridge University Press
Peer Reviewed Peer Reviewed
Volume 18
Issue S381
Pages 13-16
Keywords Astronomy and Astrophysics; Space and Planetary Science
Public URL


You might also like

Downloadable Citations