Fuzzy Dark Matter as a Solution to Reconcile the Stellar Mass Density of High-z Massive Galaxies and Reionization History

TL;DR

This paper proposes fuzzy dark matter with ultra-light axions as a solution to reconcile high stellar mass densities observed by JWST at high redshifts with cosmic reionization constraints, by suppressing small halo formation.

Contribution

It demonstrates that fuzzy dark matter with specific axion masses can simultaneously match JWST galaxy data and reionization history, addressing a key inconsistency in cosmology.

Findings

FDM with $m_a \,\sim\, 5\times10^{-23}$ eV suppresses small halo formation.

This FDM model aligns JWST high-z galaxy data with reionization constraints.

Warm dark matter with keV mass could have similar effects as FDM.

Abstract

The JWST early release data show unexpected high stellar mass densities of massive galaxies at $7<z<11$, a high star formation efficiency is probably needed to explain this. However, such a high star formation efficiency would greatly increase the number of ionizing photons, which would be in serious conflict with the current cosmic microwave background (CMB) and other measurements of cosmic reionization history. To solve this problem, we explore the fuzzy dark matter (FDM), which is composed of ultra-light scalar particles, e.g. ultra-light axions, and calculate its halo mass function and stellar mass density for different axion masses. We find that the FDM model with $m_a\simeq 5\times10^{-23} \rm eV$ and a possible uncertainty range $\sim3\times10^{-23}-10^{-22}\, \rm eV$ can effectively suppress the formation of small halos and galaxies, so that with higher star formation efficiency, both the JWST data at $z\sim8$ and the reionization history measurements from the optical depth of CMB scattering and ionization fraction can be simultaneously matched. We also find that the JWST data at $z\sim10$ are still too high to fit in this scenario. We note that the estimated mean redshift of the sample may have large uncertainty, that it can be as low as $z\sim9$ depending on adopted spectral energy distribution (SED) templates and photometric-redshift code. Besides, the warm dark matter with $\sim$keV mass can also be an alternative choice, since it should have similar effects on halo formation as the FDM.