Abstract

The JWST is revolutionizing our understanding of the early Universe by unveiling a wealth of bright galaxies at z>9 and faint AGNs at z>5. I will present the latest constraints on the overabundance of UV-bright galaxies at z>9, which is 10-100 times higher than galaxy formation models, and summarize to what extent recent theoretical efforts can reproduce such observations. I will show how future wide-area surveys such as Euclid will help put stronger constraints ion the bright-end of UVLF at z>8. On the other hand, faint galaxies, representing the building blocks of present-day galaxies, have eluded spectroscopic constraints, even with the deepest JWST campaigns so far. I will present the results of our UNCOVER survey, which combines ultra-deep NIRSpec spectroscopy with the strong lensing magnification of A2744 cluster. We characterize ultra-faint galaxies with intrinsic absolute magnitude between Muv=-17 and Muv=-15 at 6<z<8, and stellar masses down to 10^6 solar masses, which are likely the drivers of cosmic reionization. I will discuss our plans to obtain the deepest observations on sky with the GLIMPSE program to the faintest galaxy population out to z=15 and beyond.