The Denoised, Deconvolved, and Decomposed Fermi gamma-ray sky

Abstract

We analyze the 6.5 year all-sky data from the Fermi Large Area Telescope in the energy range 0.6–307.2 GeV. Raw count maps show a superposition of diffuse and point-like emission structures and are subject to shot noise and instrumental artifacts. Using the Denoising, Deconvolving, and Decomposing Photon Observations D3PO algorithm, we modeled the observed photon counts as the sum of a diffuse and a point-like photon flux, convolved with the instrumental beam and subject to Poissonian shot noise, without the use of spatial or spectral templates. The D3PO algorithm performs a Bayesian inference and yields separate estimates for the two flux components. We show that the diffuse γ-ray flux can be described phenomenologically by only two distinct components: a soft component, presumably dominated by hadronic processes, tracing the dense, cold interstellar medium, and a hard component, presumably dominated by leptonic interactions,following the hot and dilute medium and outflows such as the Fermi bubbles.