Milky Way Satellite Census. IV. Constraints on Decaying Dark Matter from Observations of Milky Way Satellite Galaxies

Understand

We use a recent census of the Milky Way (MW) satellite galaxy population to constrain the lifetime of particle dark matter (DM).

• We consider two-body decaying dark matter (DDM) in which a heavy DM particle decays with lifetime $\tau$ comparable to the age of the Universe to a lighter DM particle (with mass splitting $\epsilon$) and to a dark radiation species.
• These decays impart a characteristic "kick velocity," $V_{\mathrm{kick}}=\epsilon c$, on the DM daughter particles, significantly depleting the DM content of low-mass subhalos and making them more susceptible to tidal disruption.
• We fit the suppression of the present-day DDM subhalo mass function (SHMF) as a function of $\tau$ and $V_{\mathrm{kick}}$ using a suite of high-resolution zoom-in simulations of MW-mass halos, and we validate this model on new DDM simulations of systems specifically chosen to resemble the MW.