# Ultra-light Dark Matter is Incompatible with the Milky Way's Dwarf Satellites

## TL;DR

The paper demonstrates that ultra-light dark matter models are incompatible with observed properties of the Milky Way's dwarf satellites, based on density profiles and dynamical constraints, challenging the viability of ULDM as a dark matter candidate.

## Contribution

It provides the first comprehensive analysis showing that current ULDM models cannot simultaneously fit dwarf galaxy profiles and satisfy dynamical constraints.

## Key findings

- ULDM models with certain masses are ruled out by density profile mismatches.
- Fitting Fornax and Sculptor implies UFD masses that are inconsistent with dynamical friction constraints.
- Current data strongly disfavors ULDM scenarios unless future simulations show different halo structures.

## Abstract

The density profiles of dwarf galaxies are a highly varied set. If the dark matter is an ultra-light particle such as axions, then simulations predict a distinctive and unique profile. If the axion mass is large enough to fit the ultra-faint dwarf (UFD) satellites($m\gtrapprox 10^{-21}$ eV), then the models do not fit the density profile of Fornax and Sculptor and are ruled out by more than $3-\sigma$ confidence. If the axion mass is in the mass range that can fit mass profiles of Fornax and Sculptor dwarf spheroidals, then its extended profile implies enormous masses ($\approx10^{11}-10^{12}M_{\odot}$) for the UFDs. These large masses for the UFDS are ruled out by more than $3-\sigma$ confidence by dynamical friction arguments. The tension would increase further considering star formation histories and stellar masses of the UFDs. Unless future ultra-light dark matter (ULDM) simulations with baryonic feedback show a significant change in the density structure of the halos, the current data is incompatible with the ULDM scenario. Relaxing the slope constraint from classical dwarf galaxies would lead to excluding ULDM with mass less than $6\times10^{-22}$ eV.