On the maximum disk heating attributable to fuzzy dark matter

Abstract

Fuzzy dark matter (FDM) granulations would drive orbital transport of stars in galactic disks, and in particular would produce roughly equal amounts of radial heating and radial migration. However, observations suggest that heating has been much less efficient than migration in our Galaxy. We argue that this decreases the amount of radial heating, $\mathcal{H}_\mathrm{FDM}$, that can safely be attributed to FDM. Consequently, lower bounds on the FDM particle mass $m$ derived through Galactic disk kinematics should be revised upwards; a rough estimate is $m \gtrsim 1.3\times 10^{-22} \mathrm{eV} \times [(\mathcal{H}_\mathrm{FDM}/\mathcal{H})/0.1]^{-1/2}$, where $\mathcal{H}$ is the total observed radial heating.