2025ApJ...987..194C

Wide-separation lensed quasars (WSLQs) are a rare class of strongly lensed quasars, magnified by foreground massive galaxy clusters, with typically large magnifications of the multiple quasar images. They are a relatively unexplored opportunity for detailed study of quasar host galaxies. The current small sample of known WSLQs has a median redshift of z ≈ 2.1, larger than most other samples of quasar host galaxies studied to date. Here, we derive precise constraints on the properties of six WSLQs and their host galaxies, using parametric surface brightness fitting, measurements of quasar emission lines, and stellar population synthesis of host galaxies in six WSLQ systems. Our results, with significant uncertainty, indicate that these six hosts are a mixture of star-forming and quiescent galaxies. To probe for coevolution between active galactic nuclei (AGNs) and host galaxies, we model the offset from the “local” (z = 0) M_BH-M_⋆ relation as a simple power law in redshift. Accounting for selection effects, a WSLQ-based model for evolution in the M_BH-M_⋆ relation has a power-law index of γ_M = -0.42 ± 0.31, consistent with no evolution. Compared to several literature samples, which mostly probe unlensed quasars at z < 2, the WSLQ sample shows less evolution from the local relation, at ∼4σ. We find that selection effects and choices of M_BH calibration are the most important systematics in these comparisons. Given that we resolve host galaxy flux confidently even from the ground in some instances, our work demonstrates that WSLQs and highly magnified AGNs are exceptional systems for future AGN-host coevolution studies.