The Impact of Fuzzy Dark Matter Dynamics on the Accumulation and Fragmentation of Primordial Gas

TL;DR

This study explores how Fuzzy Dark Matter influences primordial gas dynamics, delaying star formation and shifting it away from central regions, which impacts early universe observations.

Contribution

It provides a physical framework for understanding how FDM suppresses and delays star formation in small halos compared to CDM, affecting cosmic dawn timing.

Findings

Gas collapse is delayed by FDM solitonic core geometry.

Wave fluctuations disrupt gas accumulation and angular momentum.

Star formation sites shift to lower-mass clusters away from centers.

Abstract

Fuzzy Dark Matter (FDM), particularly in the $10^{-22}$ eV mass regime is frequently used to characterize wave-like interference effects. It exhibits macroscopic wave properties, which drive distinct baryonic dynamics within collapsed haloes. Using the hydrodynamical code AREPO with the AxiREPO module and primordial chemistry, we simulate the assembly of haloes with masses $3 \times 10^{8} \le M_{\mathrm{h}} \le 8 \times 10^{9} \: M_\odot$ across a range of axion masses $1 \times 10^{-22} \le m_{\mathrm{a}} \le 7 \times 10^{-22}$ eV. We investigate how small-scale dynamics of the FDM density field affect the accumulation of cold, dense gas essential for primordial star formation. We demonstrate that gas collapse is suppressed by a two-fold mechanism: a delay driven by the geometry of the FDM solitonic core and a secondary dynamical barrier caused by stochastic wave fluctuations. While the flattened solitonic potential profile itself inhibits central gas accumulation, these wave-driven dynamics provide a further layer of disruption and angular momentum support, which in certain regimes prevents gas from reaching the central, compact, high-density configurations characteristic of CDM. Consequently, sites of star formation are shifted away from a single central peak toward a population of lower-mass clusters. Our work provides a physical framework for calibrating halo mass-dependent star formation efficiencies in FDM cosmologies, where internal processes may delay Cosmic Dawn beyond the effects of the initial power spectrum cut-off. These results are essential for interpreting realistic observational constraints from future 21-cm signal observations and the faint-end luminosity functions observed by the JWST, as well as providing an upper bound on the baryonic effects in the context of Mixed Dark Matter scenarios.