Predictions for the Abundance of High-redshift Galaxies in a Fuzzy Dark Matter Universe

Abstract

During the last decades, rapid progress has been made in measurements of the rest-frame ultraviolet (UV) luminosity function (LF) for high-redshift galaxies ($z \geq 6$). The faint-end of the galaxy LF at these redshifts provides powerful constraints on different dark matter models that suppress small-scale structure formation. In this work we perform full hydrodynamical cosmological simulations of galaxy formation using an alternative DM model composed of extremely light bosonic particles ($m \sim 10^{-22}$ eV), also known as fuzzy dark matter (FDM), and examine the predictions for the galaxy stellar mass function and luminosity function at $z \geq 6$ for a range of FDM masses. We find that for FDM models with bosonic mass $m = 5\times10^{-22}$ eV, the number density of galaxies with stellar mass $\rm M_* \sim 10^7 M_{\odot}$ is suppressed by $\sim 40\%$ at z = 9, $\sim 20\%$ at z = 5, and the UV LFs within magnitude range of -16 < $M_{\rm UV}$ < -14 is suppressed by $\sim 60\%$ at $z = 9$, $\sim 20\%$ at $z = 5$ comparing to the CDM counterpart simulation. Comparing our predictions with current measurements of the faint-end LFs ($-18 \leqslant M_{\rm UV} \leqslant -14$), we find that FDM models with $m_{22} < 5\times10^{-22}$ are ruled out at $3\sigma$ confidence level. We expect that future LF measurements by James Webb Space Telescope (JWST), which will extend down to $M_{\rm UV} \sim -13$ for $z \lesssim 10$, with a survey volume that is comparable to the Hubble Ultra Deep Field (HUDF) would have the capability to constrain FDM models to $m\; \gtrsim 10^{-21}$ eV.