Opening extreme galaxy observations through individual stars in cosmological distances
Invited Talk, EAS2025, Cork, Ireland
Since the launch of the James Webb Space Telescope (JWST), extragalactic astronomy studies have been completely revolutionized by its unprecedented spatial resolution and sensitivity. In particular, the JWST’s capability not only allows us to detect galaxies in the very high-redshift Universe but also even allows us to access each single star that exists within each distant galaxy with the aid of caustic crossings over the strong gravitational lensings (e.g., Mothra; Diego+23, Earendel; Welch+23). Such single stars were also previously detected as transient micro-lensing events caused by time variations of critical curves (e.g., Icarus; Kelly+18). These observations of lensed individual stars provide us with the extreme opportunity for extragalactic study; stellar physics in distant galaxies. However, previous magnified individual star observations are limited to a very small number of sources — typically one to a few stars in each galaxy— and provide only limited information about stellar populations at cosmological distances. With the unprecedented JWST’s time-domain observations of distant highly magnified galaxies, the situation has been completely changed. Starting from the recent reports of more than 40 micro-lensed stars within a galaxy at z=0.725 (Fudamoto+25), cycle-4 JWST observations will open statistical observations of hundreds of individual stars around the cosmic noon, using multiple JWST filters. In this talk, I summarize recent progress of distant star observations, as well as introduce our upcoming JWST’s deep multi-cadence, multi-filter, microlensing survey of stars in a cosmological distances.