Soliton Oscillations and Revised Constraints from Eridanus II of Fuzzy Dark Matter

TL;DR

This paper investigates the oscillatory behavior of fuzzy dark matter solitons, demonstrating that their effects on star clusters are negligible and revising previous constraints on the dark matter particle mass.

Contribution

It provides new analytical and numerical evidence that soliton oscillations do not significantly impact star clusters, challenging prior constraints on fuzzy dark matter.

Findings

Soliton oscillations persist after tidal stripping.

Gravitational heating of star clusters by solitons is negligible.

Subhalo mass function does not strongly constrain particle mass.

Abstract

Fuzzy dark matter (FDM) has been a promising alternative to standard cold dark matter. The model consists of ultralight bosons with mass $m_b \sim 10^{-22}$ eV and features a quantum-pressure-supported solitonic core that oscillates. In this work, we show that the soliton density oscillations persist even after significant tidal stripping of the outer halo. We report two intrinsic yet distinct timescales associated, respectively, with the ground-state soliton wavefunction $\tau_{00}$ and the soliton density oscillations $\tau_\text{soliton}$, obeying $\tau_\text{soliton} /\tau_{00} \simeq 2.3$. The central star cluster (SC) in Eridanus II has a characteristic timescale $\tau_\text{soliton} / \tau_\text{SC} \sim 2$ to $3$ that deviates substantially from unity. As a result, we demonstrate, both analytically and numerically with three-dimensional self-consistent FDM simulations, that the gravitational heating of the SC owing to soliton density oscillations is negligible irrespective of $m_b$. We also show that the subhalo mass function to form Eridanus II does not place a strong constraint on $m_b$. These results are contrary to the previous findings by Marsh & Niemeyer (2019).