Discovery of a Low-mass Strong-lens System in SMACS J0723.3−7327

Abstract 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>″</mml:mi> </mml:mrow> </mml:mover> </mml:math> 424 ± 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>″</mml:mi> </mml:mrow> </mml:mover> </mml:math> 012, stellar mass of M * = (3.3 ± 0.8) × 10 10 M ⊙ , 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 10.5 M ⊙ , 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.