Dark-matter decays and Milky Way satellite galaxies

TL;DR

This paper investigates how decaying dark matter models affect Milky Way satellite galaxies, using observational data to constrain particle lifetime and recoil speed, and suggests future surveys for improved constraints.

Contribution

It provides new constraints on dark-matter decay parameters using satellite galaxy properties and highlights the importance of upcoming surveys for probing dark matter.

Findings

Constraints exclude tau >~ 30 Gyr for certain v_k ranges.

Satellite mass distribution is a key probe of dark-matter decay.

Limits on decay parameters depend on star-formation histories.

Abstract

We consider constraints on a phenomenological dark-matter model consisting of two nearly degenerate particle species using observed properties of the Milky Way satellite galaxy population. The two parameters of this model, assuming the particle masses are >~ GeV, are v_k, the recoil speed of the daughter particle, and tau, the lifetime of the parent particle. The satellite constraint that spans the widest range of v_k is the number of satellites that have a mass within 300 pc M300 > 5 x 10^6 solar masses, although constraints based on M300 in the classical dwarfs and the overall velocity function are competitive for v_k >~ 50 km/s. In general, we find that tau <~ 30 Gyr is ruled out for 20 km/s <~ v_k <~ 200 km/s, although we find that the limits on tau for fixed v_k can change constraints by a factor of ~3 depending on the star-formation histories of the satellites. We advocate using the distribution of M300 in Milky Way satellites determined by next-generation all-sky surveys and follow-up spectroscopy as a probe of dark-matter properties.