New Bounds on Fuzzy Dark Matter from Galaxy-Galaxy Strong-Lensing Observations

TL;DR

This paper uses galaxy-galaxy strong lensing observations to place new constraints on fuzzy dark matter, showing that FDM with mass below 10^{-24} eV cannot constitute more than 10% of total dark matter, closing a previously open mass window.

Contribution

It introduces a hybrid FDM+NFW model to analyze lensing data, providing new bounds on FDM particle mass and its contribution to dark matter.

Findings

FDM with mass ≤ 10^{-24} eV cannot be more than 10% of DM.

The hybrid model reproduces observed Einstein radii under certain conditions.

Constraints effectively close the remaining FDM mass window.

Abstract

Fuzzy Dark Matter (FDM) has recently gained attention as a motivated candidate for the dark matter (DM) content of the Universe, as opposed to the commonly assumed cold DM (CDM), since the soliton profile intrinsic to FDM models was found to be particularly well suited to reproduce observed galaxy mass profiles. While FDM as a single DM component has been strongly constrained by multiple probes, there remained a mass window between $10^{-25}\,\mathrm{eV}$ and $10^{-24}\,\mathrm{eV}$ in which it can comprise a large portion ($\gtrsim\mathcal{O}(10\%)$) of the total DM. In this work, we consider gravitational lensing measurements in the strong lensing regime, which are one of the only means to directly constrain the distribution and profile of DM in astronomical bodies. Using a simple model that combines a soliton FDM component with a Navarro-Frenk-White (NFW) profile, we explore under what conditions DM halos with this hybrid profile are able to reproduce the observed Einstein radii of several known lenses. We find that FDM with a particle mass of $\lesssim 10^{-24}\,{\rm eV}$ cannot explain the observations if it makes up more than $\sim10\%$ of the total DM, effectively closing the lingering FDM mass window.