# Spatially Resolved Stellar Kinematics of the Ultra-Diffuse Galaxy Dragonfly 44: II. Constraints on Fuzzy Dark Matter

## TL;DR

This study uses stellar kinematics of the ultra-diffuse galaxy Dragonfly 44 to constrain fuzzy dark matter properties, finding a scalar field mass consistent with galaxy dynamics but conflicting with Lyα forest constraints, and supporting key fuzzy DM predictions.

## Contribution

The paper provides the first constraints on fuzzy dark matter from stellar dynamics of an ultra-diffuse galaxy, linking observations to theoretical halo predictions.

## Key findings

- Inferred fuzzy DM scalar field mass of ~3 x 10^{-22} eV.
- Fuzzy DM halo properties align with core size--halo mass relations.
- Results are consistent with fuzzy DM predictions but tension with Lyα forest constraints.

## Abstract

Given the absence of directly detected dark matter (DM) as weakly interacting massive particles, there is strong interest in the possibility that DM is an ultra-light scalar field, here denoted as fuzzy DM. Ultra-diffuse galaxies, with the sizes of giant galaxies and the luminosities of dwarf galaxies, have a wide range of DM halo masses, thus providing new opportunities for exploring the connections between galaxies and their DM halos. Following up on new integral field unit spectroscopic observations and dynamics modeling of the DM-dominated ultra-diffuse galaxy Dragonfly 44 in the outskirts of the Coma Cluster, we present models of fuzzy DM constrained by the stellar dynamics of this galaxy. We infer a scalar field mass of $\sim 3 \times 10^{-22}$ eV, consistent with other constraints from galaxy dynamics but in tension with constraints from Ly$\alpha$ forest power spectrum modeling. While we are unable to statistically distinguish between fuzzy DM and normal cold DM models, we find that the inferred properties of the fuzzy DM halo satisfy a number of predictions for halos in a fuzzy DM cosmology. In particular, we find good agreement with the predicted core size--halo mass relation and the predicted transition radius between the quantum pressure-dominated inner region and the outer halo region.