Extragalactic microlensing through Ultra Diffuse Galaxies

Stellar microlensing is a powerful method to constrain compact dark matter models, uncover binary stars, and exoplanets during caustic crossing events. At cosmological distances, James-Webb Space Telescope (JWST) is routinely detecting microlensed giant stars in highly magnified galaxies behind massive lensing clusters. Here, we explore for the first time microlensing in modest redshift galaxies commonly seen through local Ultra Diffuse Galaxies (UDGs). Using the UDG NGC1052-DF2 as a proof-of-concept, we find that detecting microlensing events through UDGs is possible. Euclid is ideal for identifying samples of low-redshift star-forming galaxies seen through local galaxies for deeper cadenced follow-up, where our zeroth-order calculation estimates that O(1-10) events per year are expected over the whole sky under the monitoring of LSST, assuming all UDGs share similar distance and stellar content as NGC1052-DF2. Such measurements can help settle the DM issue for UDG galaxies by providing a stellar mass estimate weighted more by the low end of the stellar initial mass function (IMF) than standard stellar synthesis estimates. Note, lower efficiency is estimated for JWST of about 5.6 times10-2, yr-1 over its five background galaxies is expected for typical JWST about29,mag visits, and a low Vera Rubin Legacy Survey of Space and Time (LSST) detection rate of about 0.03, yr-1 such that NGC1052-DF2 might not be a prime target given its lack of low-redshift background galaxies.