Three years of searching for the most distant galaxies with JWST and what have we learned so far?

Speaker: L.Y. Aron Yung, Space Telescope Science Institute

Abstract: The superb capabilities of the James Webb Space Telescope (JWST) have extended our view to the ultra-high-redshift universe (z > 12). Among numerous scientific discoveries enabled by JWST, some early deep extragalactic observations have unexpectedly revealed an abundance of massive galaxies, presenting significant challenges to conventional galaxy formation models. To address this cosmic puzzle, we utilize some well-established galaxy formation models in conjunction with state-of-the-art cosmological simulations to seek understanding of physical mechanisms that enabled extremely rapid star formation activities in the early universe.  We investigated and quantified the impact of various sources of uncertainty, including a potentially evolving mass-to-light ratio driven by changes in the IMF, underestimated field-to-field variance, and significant uncertainties in photometric redshifts, among others. Our study also examines the number density of halo populations during this epoch, alongside the gas cooling rates and star formation efficiencies of galaxies. We find that the stellar feedback models currently implemented in our framework—and widely adopted in many hydrodynamic simulations—eject gas at rates comparable to halo mass accretion rates. This process deprives galaxies of the necessary fuel for star formation. I will present new simulated results for various alternative star formation and stellar feedback models, discussing the essential conditions required to reproduce the observed ultra-high-redshift galaxy populations.