Diffuse gamma-ray constraints on dark matter revisited. I: the impact of subhalos

Abstract

We make a detailed analysis of the indirect diffuse gamma-ray signals from dark matter annihilation in the Galaxy. We include the prompt emission, as well as the emission from inverse Compton scattering whenever the annihilation products contain light leptons. We consider both the contribution from the smooth dark matter halo and that from substructures. The main parameters for the latter are the mass function index and the minimal subhalo mass. We use recent results from N-body simulations to set the most reasonable range of parameters, and find that the signal can be boosted by a factor ranging from 2 to 15 towards the Galactic poles, slightly more towards the Galactic anticenter, with an important dependence on the subhalo mass index. This uncertainty is however much less than that of the extragalactic signal studied in the literature. We derive upper bounds on the dark matter annihilation cross section using the isotropic gamma-ray emission measured by Fermi-LAT, for two directions in the sky, the Galactic anticenter and the Galactic pole(s). The former represents the lowest irreducible signal from dark matter annihilation, and the latter is robust as the astrophysical background, dominated by the hadronic contribution, is rather well established in that direction. Finally, we show how the knowledge of the minimal subhalo mass, which formally depends on the dark matter particle interactions with normal matter, can be used to derive the mass function index.

32 pages. V2: changes to match the version accepted for publication in JCAP

References in corpus (20)

• PYTHIA 6.4 Physics and Manual
• Observation of an anomalous positron abundance in the cosmic radiation
• Measurement of the Cosmic Ray e+ plus e- spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope
• Precise Relic WIMP Abundance and its Impact on Searches for Dark Matter Annihilation
• The Spectrum of the Isotropic Diffuse Gamma-Ray Emission Derived From First-Year Fermi Large Area Telescope Data
• A Tentative Gamma-Ray Line from Dark Matter Annihilation at the Fermi Large Area Telescope
• On the local dark matter density
• Galactic secondary positron flux at the Earth
• Galactic electrons and positrons at the Earth:new estimate of the primary and secondary fluxes
• Inverse Compton constraints on the Dark Matter e+e- excesses
• Dark Matter Annihilation in Substructures Revised
• Galactic Substructure and Dark Matter Annihilation in the Milky Way Halo
• Cosmic Gamma-Ray Background from Star-Forming Galaxies
• Joint anisotropy and source count constraints on the contribution of blazars to the diffuse gamma-ray background
• Dark Matter Indirect Signatures
• 10 GeV dark matter candidates and cosmic-ray antiprotons
• A possible approach to three-dimensional cosmic-ray propagation in the Galaxy IV. Electrons and electron-induced gamma-rays
• Impact of the spectral hardening of TeV cosmic rays on the prediction of the secondary positron flux
• Antiprotons from Dark Matter: Effects of a Position-Dependent Diffusion Coefficient
• SZ effects from annihilating dark matter in the Milky Way: smooth halo, subhalos and intermediate-mass-black-holes

Cited by in corpus (4)

• Gamma Ray Signals from Dark Matter: Concepts, Status and Prospects
• Hierarchical Formation of Dark Matter Halos and the Free Streaming Scale
• Modeling dark matter subhalos in a constrained galaxy: Global mass and boosted annihilation profiles
• The viability of low-mass subhaloes as targets for gamma-ray dark matter searches