Strong gravitational lensing occurs when a massive foreground galaxy bends and magnifies the light of a more distant source galaxy, which makes lensing systems a unique opportunity to study both the foreground mass distribution and the properties of background sources at high redshift. The Euclid space telescope was launched to map the dark universe. Its high-resolution imaging, near-infrared photometry and spectroscopy establish it as a new tool for discovering an unprecedented amount of lensing systems. This project focuses on previously unstudied strong lens candidates identified in the Euclid Q1 Quick Release, where photometry and lens modelling are combined with spectral energy distribution (SED) fitting in a reproducible analysis pipeline to characterise the constituent galaxies. Lenstronomy was used to reconstruct lens system geometries and obtain enclosed masses, giving Einstein radii between 0. 7″ and 0. 9″. The total masses within the Einstein radius were calculated at ~1012M☉, with dark matter fractions ranging from 35-80%. BAGPIPES fits to both lens and source galaxy photometry revealed the lenses are massive quenched ellipticals with stellar masses log (M_*/M_☉) ≈ 11. 3-11. 6. The source galaxy’s data suggests they’re at two evolutionary stages, where one is a transitional system at z ≈ 1. 5 with a declining star formation timescale, and the other is a dusty starburst at z ≈ 3 with a star formation rate at 1 x 103 M☉ yr⁻¹. The results of the study therefore show interpretable measurements of lens masses, magnification, and stellar populations from imaging. It has been found that metallicity and dust cannot yet be reliably characterised by broadband SED fitting alone, which has established the need for spectroscopic follow-up. Overall, the project highlights Euclid’s potential for expanding gravitational lensing science, whilst enabling systematic studies of baryonic and dark matter in galaxies across cosmic time.
Cath Lister (Wed,) studied this question.