LEDA 2018 - 2023

Highlights

Probing the dark matter distribution on scales of a few hundred parsecs requires angular resolutions of a few milliarcseconds. At present, such resolution is achievable only with interferometric arrays operating at centimetre and millimetre wavelengths. To analyse these data, our ERC-funded group has developed a novel gravitational-lens modelling framework that fits the observations directly in visibility space. Applying this technique to milliarcsecond-resolution data obtained with the Global Very Long Baseline Interferometry network (EVN+VLA), we have placed competitive constraints on fuzzy dark matter using a single lens system. Additionally, we have gravitationally imaged what is possibly the lowest-mass dark-matter halo detected so far. In parallel, we have developed a comprehensive lens-modelling code that enables the simultaneous and self-consistent inference of the lensed source’s polarisation properties, the lens mass distribution, and the magnetic and ionised structure of the lens galaxy’s interstellar medium. This approach opens a unique window onto the strength and topology of magnetic fields in galaxies at cosmological distances, well beyond the reach of direct observations.

Members

Simona Vegetti
Simon Ndiritu
Devon Powell
Hannah Stacey

Publications

A possible challenge for cold and warm dark matter. Vegetti et al. (2026), Published in Nature Astronomy

A million-solar-mass object detected at a cosmological distance using gravitational imaging. Powell et al. (2025), Published in Nature Astronomy

Investigation of mass substructure in the gravitational lens system SDP.81 with ALMA long-baseline observations. Stacey et al. (2025), Accepted for publication in MNRAS

A self-consistent framework to study magnetic fields with strong gravitational lensing and polarised radio sources. Ndiritu et al. (2025), MNRAS, 538, 671

Complex angular structure of three elliptical galaxies from high-resolution ALMA observations of strong gravitational lenses. Stacey et al. (2024), A&A, 688, A110

Strong gravitational lensing as a probe of dark matter. Vegetti et al. (2024), Space Science Reviews, 220, 58

A lensed radio jet at milli-arcsecond resolution - II. Constraints on fuzzy dark matter from an extended gravitational arc. Powell et al. (2023), MNRAS, 524, 84

A lensed radio jet at milliarcsecond resolution I: Bayesian comparison of parametric lens models. Powell et al. (2022), MNRAS, 516, 1808

A novel approach to visibility-space modelling of interferometric gravitational lens observations at high angular resolution. Powell et al. (2021), MNRAS, 501, 515

The rocky road to quiescence: compaction and quenching of quasar host galaxies at z ∼ 2. Stacey et al. (2020), MNRAS, 500, 3667