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Arxiv: JWST Discovery of 40+ Microlensed Stars in a Magnified Galaxy, the "Dragon" behind Abell 370 Published: 4/11/2024 9:00:02 PM Updated: 4/11/2024 9:00:02 PM

Paper abstract: Strong gravitational magnification by massive galaxy clusters enable us todetect faint background sources, resolve their detailed internal structures,and in the most extreme cases identify and study individual stars in distantgalaxies. Highly magnified individual stars allow for a wide range ofapplications, including studies of stellar populations in distant galaxies andconstraining small-scale dark matter structures. However, these applicationshave been hampered by the small number of events observed, as typically one ora few stars are identified from each distant galaxy. Here, we report thediscovery of 46 significant microlensed stars in a single strongly-lensedhigh-redshift galaxy behind the Abell 370 cluster at redshift of 0.725 when theUniverse was half of its current age (dubbed the ``Dragon arc''), based on twoobservations separated by one year with the James Webb Space Telescope ({\itJWST}). These events are mostly found near the expected lensing criticalcurves, suggesting that these are magnified individual stars that appear astransients from intracluster stellar microlenses. Through multi-wavelengthphotometry and colors, we constrain stellar types and find that many of themare consistent with red giants/supergiants magnified by factors of thousands.This finding reveals an unprecedented high occurrence of microlensing events inthe Dragon arc, and proves that {\it JWST}'s time-domain observations open upthe possibility of conducting statistical studies of high-redshift stars andsubgalactic scale perturbations in the lensing dark matter field.