Monsters in the Dark: Searching Far and Wide for Ultra-Luminous Galaxies at Cosmic Dawn

John Weaver examines unusually bright galaxies as probes of rapid early galaxy formation. Galaxies beyond redshift 10 are scarce and difficult to study, so luminous analogues at redshifts around 7–9 provide complementary tests. A search across 50 square degrees of Euclid deep-field data identifies objects reaching an ultraviolet absolute magnitude of −24, about ten times the luminosity of GNz-11, constraining the previously poorly measured bright end of the ultraviolet luminosity function. Spatially resolved JWST NIRSpec observations of a luminous galaxy near redshift 8 reveal its morphology, assembly history and internal properties. These results illustrate why resolved spectroscopy will be important for interpreting the larger populations expected from Euclid and Roman.