New Roads to the Small-scale Universe: Measurements of the Clustering of Matter with the High-redshift UV Galaxy Luminosity Function

The epochs of cosmic dawn and reionization present promising avenues for understanding the role of dark matter (DM) in our cosmos. The first galaxies that populated the universe during these eras resided in DM halos that were much less massive than their counterparts today. Consequently, observations of such galaxies can provide us with a handle on the clustering of DM in an otherwise currently inaccessible regime. In this work, we use high-redshift UV galaxy luminosity function (UV LF) data from the Hubble Space Telescope to study the clustering properties of DM at small scales. In particular, we present new measurements of the matter power spectrum at wavenumbers 0.5 Mpc-1 < k < 10 Mpc-1 to roughly 30% precision, obtained after marginalizing over the unknown astrophysics. These new data points cover the uncharted redshift range 4 ≤ z ≤ 10 and encompass scales beyond those probed by cosmic microwave background and large-scale structure observations. This work establishes the UV LF as a powerful tool to probe the nature of DM in a different regime than other cosmological and astrophysical data sets.