High-redshift, small-scale tests of ultralight axion dark matter using Hubble and Webb galaxy UV luminosities

Understand

We calculate the abundance of UV-bright galaxies in the presence of ultralight axion (ULA) dark matter (DM), finding that axions suppress their formation with a non-trivial dependence on redshift and luminosity.

• We set limits on axion DM using both Planck cosmic microwave background (CMB) and UV luminosity function (UVLF) data.
• We exclude a single axion as all the DM for $m_{ax} < 10^{-21.6}$ eV and limit axions with $-26 < \log( m_{ax}/{eV}) < -23$ to be less than $22\%$ of the DM (both limits at $95\%$ credibility).
• These limits use UVLF measurements from 24,000 sources from the Hubble Space Telescope (HST) that probe small-scale structure at redshifts $4 < z < 10$.