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Arxiv: High-redshift, small-scale tests of ultralight axion dark matter using Hubble and Webb galaxy UV luminosities Published: 4/17/2024 8:01:42 AM Updated: 5/1/2024 8:55:16 PM

Paper abstract: We calculate the abundance of UV-bright galaxies in the presence ofultralight axion (ULA) dark matter (DM), finding that axions suppress theirformation with a non-trivial dependence on redshift and luminosity. We setlimits on axion DM using both Planck cosmic microwave background (CMB) and UVluminosity function (UVLF) data. We exclude a single axion as all the DM form_{ax} < 10^{-21.6} eV and limit axions with -26 < \log( m_{ax}/{eV}) < -23to be less than 22\% of the DM (both limits at 95\% credibility). Theselimits use UVLF measurements from 24,000 sources from the Hubble SpaceTelescope (HST) that probe small-scale structure at redshifts 4 < z < 10. Wemarginalize over a parametric model that connects halo mass and UV luminositythat has been shown to match hydrodynamical simulations. Our results bridge awindow in axion mass and DM fraction previously unconstrained by cosmologicaldata, between large-scale CMB and galaxy clustering and the small-scaleLyman-\alpha forest. These high-z measurements provide a powerfulconsistency check of low-z tests of axion DM, which include the recent hintfor a sub-dominant ULA DM fraction in Lyman-\alpha forest data. We alsoconsider a sample of 25 spectroscopically-confirmed high-z galaxies from theJames Webb Space Telescope (JWST). We find that these data are consistent withthe HST UVLF assuming \LambdaCDM and our flexible parametric model of UVluminosity. Combining HST and JWST UVLF data does not improve our constraintsbeyond HST alone, but future JWST measurements have the potential to improvethese results significantly. We also find an excess of low-mass halos (< 10^9M_\odot) at z < 3, which could be probed by sub-galactic structure probes(e.g., stellar streams, satellite galaxies and strong lensing).