Complex angular structure of three elliptical galaxies from high-resolution ALMA observations of strong gravitational lenses

¹ European Southern Observatory (ESO), Karl-Schwarzschild Str. 2, 85748 Garching bei München, Germany
e-mail: hannah.stacey@eso.org
² Max Planck Institute for Astrophysics, Karl-Schwarzschild Str. 1, 85748 Garching bei München, Germany
³ Kapteyn Astronomical Institute, University of Groningen, Postbus 800 9700 AV Groningen, The Netherlands
⁴ South African Radio Astronomy Observatory (SARAO), PO Box 443 Krugersdorp 1740, South Africa
⁵ Department of Physics, University of Pretoria, Lynnwood Road, Hatfield, Pretoria 0083, South Africa
⁶ Department of Physics and Astronomy, University of California Davis, 1 Shields Avenue, Davis, CA 95616, USA

Received: 23 February 2024
Accepted: 17 April 2024

Abstract

The large-scale mass distributions of galaxy-scale strong lenses have long been assumed to be well described by a singular ellipsoidal power-law density profile with external shear. However, the inflexibility of this model could lead to systematic errors in astrophysical parameters inferred with gravitational lensing observables. Here, we present observations with the Atacama Large (sub-)Millimetre Array (ALMA) of three strongly lensed dusty star-forming galaxies at ≃30 mas angular resolution and investigate the sensitivity of these data to angular structure in the lensing galaxies. We jointly infer the lensing mass distribution and the full surface brightness of the lensed sources with multipole expansions of the power-law density profile up to the fourth order using a technique developed for interferometric data. All three datasets strongly favour third and fourth-order multipole amplitudes of ≈1 percent of the convergence. While the infrared stellar isophotes and isodensity shapes agree for one lens system, for the other two the isophotes disagree to varying extents, suggesting contributions to the angular structure from dark matter intrinsic or extrinsic to the lensing galaxy.