2025ApJ...982L..23D

We report the discovery of an intriguing, low-mass galaxy-scale strong-lens system in the SMACS J0723.3-7327 galaxy cluster. By modeling James Webb Space Telescope imaging and Very Large Telescope Multi-Unit Spectroscopic Explorer spectroscopic data, we find that the lens is cluster member galaxy at z = 0.397 with an Einstein radius of 0$\mathop{.}\limits^{^{\prime\prime} }$424 ± 0$\mathop{.}\limits^{^{\prime\prime} }$012, stellar mass of M_* = (3.3 ± 0.8) × 10¹⁰M_⊙, half-light radius of ∼1 kpc, and central stellar velocity dispersion of 140 ± 6 km s^–1. This lens galaxy is one of the few strong lens galaxies known to date that have stellar mass as low as M_* ∼ 10^10.5M_⊙, offering an exceptional opportunity to peek into the population of low-mass galaxies that has largely remained unexplored in the context of strong-lensing studies. This strong lens system can also assist in assessing the systematic uncertainty in the lens modeling of cluster member galaxies.