Leptons from Dark Matter Annihilation in Milky Way Subhalos

TL;DR

This study investigates how dark matter subhalos in the Milky Way influence the spectrum of high-energy electrons and positrons, showing that including subhalos improves fit to observational data and suggests a significant contribution from these structures.

Contribution

The paper demonstrates that incorporating dark matter subhalos into cosmic ray models significantly improves the fit to Fermi and PAMELA data, revealing their important role in cosmic ray spectra.

Findings

Subhalos can significantly modify electron and positron spectra.

Including subhalos improves fit to observational data.

At least a third of high-energy leptons may originate from subhalos.

Abstract

Numerical simulations of dark matter collapse and structure formation show that in addition to a large halo surrounding the baryonic component of our galaxy, there also exists a significant number of subhalos that extend hundreds of kiloparsecs beyond the edge of the observable Milky Way. We find that for dark matter (DM) annihilation models, galactic subhalos can significantly modify the spectrum of electrons and positrons as measured at our galactic position. Using data from the recent Via Lactea II simulation we include the subhalo contribution of electrons and positrons as boundary source terms for simulations of high energy cosmic ray propagation with a modified version of the publicly available GALPROP code. Focusing on the DM DM -> 4e annihilation channel, we show that including subhalos leads to a better fit to both the Fermi and PAMELA data. The best fit gives a dark matter particle mass of 1.2 TeV, for boost factors of 90 in the main halo and 1950-3800 in the subhalos (depending on assumptions about the background), in contrast to the 0.85 TeV mass that gives the best fit in the main halo-only scenario. These fits suggest that at least a third of the observed electron cosmic rays from DM annihilation could come from subhalos, opening up the possibility of a relaxation of recent stringent constraints from inverse Compton gamma rays originating from the high-energy leptons.