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Numerical simulations of dark matter collapse and structure formation showthat in addition to a large halo surrounding the baryonic component of ourgalaxy, there also exists a significant number of subhalos that extend hundredsof kiloparsecs beyond the edge of the observable Milky Way. We find that fordark matter (DM) annihilation models, galactic subhalos can significantlymodify the spectrum of electrons and positrons as measured at our galacticposition. Using data from the recent Via Lactea II simulation we include thesubhalo contribution of electrons and positrons as boundary source terms forsimulations of high energy cosmic ray propagation with a modified version ofthe publicly available GALPROP code. Focusing on the DM DM -> 4e annihilationchannel, we show that including subhalos leads to a better fit to both theFermi and PAMELA data. The best fit gives a dark matter particle mass of 1.2TeV, 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 TeVmass that gives the best fit in the main halo-only scenario. These fits suggestthat at least a third of the observed electron cosmic rays from DM annihilationcould come from subhalos, opening up the possibility of a relaxation of recentstringent constraints from inverse Compton gamma rays originating from thehigh-energy leptons.

Leptons from Dark Matter Annihilation in Milky Way Subhalos