Challenges in Revealing Dark Matter from the High Energy Gamma-Ray Background (Continuum) Ranga-Ram Chary Spitzer Science Center, Caltech

The Different Galactic Components p-p component IC Component EB component GALACTIC PLANE l~0, b~0 GALACTIC ANTICENTER l~180, b~75 Isotropic Component Hunter et al., Bertsch et al. Gas Scale Height is smaller than Radiation Field Scale Height

Contribution of Dark Matter to the E~150 MeV Background Strong Dependence on Emissivity and Halo Core Radius

Current Constraints on the Spectrum of the Residual Halo Emission: Looks more like γ -ray pulsars Isotropic EBL ~ E -2.1 Anisotropic Halo Component ~ E -1.7

Uncertainty I: Anisotropic IC

The Radiation Field R=5 kpc, z=0 kpc R=8.5 kpc, z=1.5 kpc R=5 kpc, z=1.5 kpc The Radial Scale Length of the ISRF Energy Density is ~3 kpc The Scale Height is ~1.5 kpc In contrast, gas Scale Height is ~100 pc

A Visual Approach Although the average intensity is the same, anisotropy is x greater on the right

Uncertainty II: The Cosmic Ray Spectrum and Intensity - Strong Dependence on Distance from SNR R=5 kpc, z=0 kpc R=5 kpc, z=1.5 kpc R=8.5 kpc, z=1.5 kpc

The Problem List For our galaxy: CR propagation model (Can it be done ?) Azimuthal angle dependent ISRF using more recent Sloan, Spitzer and 2MASS data To Pinpoint Dark Matter Consider: Deep GLAST pointings at edge on galaxies – still need to remove the IC component Of course, dwarf galaxies and clusters might remain the best place to identify dark matter Angular power spectrum of CGRB is likely to be dominated by unresolved blazars