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 D 3 PO 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 D 3 PO 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.

Galactic dark matter search via phenomenological astrophysics modeling

“…The "bubble-like" component showed prominently the Fermi-bubbles, as well as an puffed up version of the Galactic disc. This morphology, as well as the harder, power-law like spectrum indicates that this component is mostly due to inverse Compton up-scattering of photons by CR electrons, which predominantly occurs in the volume-dominating hot and dilute part of the ISM [41]. The Fermi bubbles are then just two giant outflows driven by the hot ISM and in particular the light CR content of it, as a number of authors already suggested [46,50].…”

“…The result of this analysis showed "cloud-like" gamma-ray emission with a spatial morphology closely resembling that of Galactic dust maps derived from completely independent microwave [48] or far-infrared [49] observations. This, as well as the steep spectrum with a hint of a bump at GeV as typical for γ-rays from the decay of π 0 s indicates that the "cloud-like" component is mostly due to hadronic CR proton interactions in the denser parts of the ISM [41]. The "bubble-like" component showed prominently the Fermi-bubbles, as well as an puffed up version of the Galactic disc.…”

“…An important observation of Selig et al [41] was that more than 90% of the DGE at all sky locations and all investigated energies could be accounted for by a simple, phenomenologically constructed two component model: The γ-ray spectra of a molecular cloud complex in the Galactic anti-center and that of the southern tip of the southern Fermi bubble [45][46][47] served as spectral templates in a point-to-point spectral fitting of the nine D 3 PO maps at different energies. The result of this analysis showed "cloud-like" gamma-ray emission with a spatial morphology closely resembling that of Galactic dust maps derived from completely independent microwave [48] or far-infrared [49] observations.…”

“…Our DGE model is based on the recent re-analysis of the Fermi γ-ray data in terms of diffuse flux and point sources by Selig et al [41]. Selig et al [41] used the D 3 PO algorithm [42] to produce noise-and point source-cleaned maps of the diffuse γ-ray emission at nine logarithmically spaced energy bands ranging from just below 1 GeV to 300 GeV. D 3 PO stands for "Denoising, deconvolving, and decomposing photon observations" and is an imaging algorithms for high energy photons.…”

“…In contrast to this, the analysis by Selig et al [41] takes marginally detected point sources into account probabilistically. Only populations of even weaker, individually unresolved point sources would be missed by D 3 PO as well.…”