Ultra-light axions, the high-redshift galaxy population and implications for the S_8 tension

          @misc{ pirsa_PIRSA:24020057,
            doi = {10.48660/24020057},
            url = {https://pirsa.org/24020057},
            author = {Rogers, Keir},
            keywords = {Cosmology},
            language = {en},
            title = {Ultra-light axions, the high-redshift galaxy population and implications for the S_8 tension},
            publisher = {Perimeter Institute},
            year = {2024},
            month = {feb},
            note = {PIRSA:24020057 see, \url{https://pirsa.org}}
          }
          

Abstract

The fundamental nature of dark matter (DM) so far eludes direct detection experiments, but it has left its imprint in the cosmic web. The standard cold DM model is remarkably well tested by cosmic microwave background and low-redshift galaxy surveys, but well-motivated particle candidates like ultra-light axions will leave signatures on small cosmic scales. These signatures are stronger at earlier times. Future 21 cm observations will transform our view of the primordial Universe, but we are already observing some of the first visible tracers of cosmic structure in the high-redshift galaxy population through the Hubble and James Webb Space Telescopes. I will present calculations of the effects of DM candidates like ultra-light axions on the high-z galaxy UV luminosity function. I will then present Hubble and Webb constraints on the allowed fraction of ULAs, accounting for uncertainties in how early galaxies trace the halo population, and discuss the implications for DM solutions to discrepancies in the late-time clustering of matter (S_8 tension).