Testing warm dark matter with kinematics of the smallest galaxies

TL;DR

This study uses galaxy kinematics to test warm dark matter models, finding that certain dwarf galaxy velocity dispersions challenge these models and setting lower bounds on dark matter particle mass.

Contribution

It introduces a method to constrain warm dark matter particle mass using dwarf galaxy kinematics and demonstrates its effectiveness with current data.

Findings

Measured velocity dispersions challenge warm dark matter predictions.

Lower bound on dark matter particle mass is set at >5.8 keV (95% confidence).

More data could tighten these constraints significantly.

Abstract

Every dark matter halo forms with a $\rho\propto r^{-1.5}$ density cusp at its center. For warm dark matter (WDM), these prompt cusps can be massive enough to influence the kinematics of dwarf galaxies. By implementing prompt cusps in the Galacticus galaxy formation model, we show that the measured velocity dispersions of Tucana V and Triangulum II are serious outliers for dwarf galaxies arising in WDM models. For thermal-relic dark matter, the three faintest Milky Way satellites together constrain the particle mass to be $m_\chi>5.8$ keV at 95 percent confidence or $m_\chi>9.4$ keV at 90 percent confidence. Improved velocity dispersion measurements for these systems could greatly refine this constraint, as could identification and kinematic characterization of more such galaxies.