SkyFACT: High-dimensional modeling of gamma-ray emission with adaptive templates and penalized likelihoods

Abstract

We present SkyFACT (Sky Factorization with Adaptive Constrained Templates), a new approach for studying, modeling and decomposing diffuse gamma-ray emission. Like most previous analyses, the approach relies on predictions from cosmic-ray propagation codes like GALPROP and DRAGON. However, in contrast to previous approaches, we account for the fact that models are not perfect and allow for a very large number ($\gtrsim 10^5$) of nuisance parameters to parameterize these imperfections. We combine methods of image reconstruction and adaptive spatio-spectral template regression in one coherent hybrid approach. To this end, we use penalized Poisson likelihood regression, with regularization functions that are motivated by the maximum entropy method. We introduce methods to efficiently handle the high dimensionality of the convex optimization problem as well as the associated semi-sparse covariance matrix, using the L-BFGS-B algorithm and Cholesky factorization. We test the method both on synthetic data as well as on gamma-ray emission from the inner Galaxy, $|\ell |<90^{\circ }$ and $|b|<20^{\circ }$, as observed by the Fermi Large Area Telescope. We finally define a simple reference model that removes most of the residual emission from the inner Galaxy, based on conventional diffuse emission components as well as components for the Fermi bubbles, the Fermi Galactic center excess, and extended sources along the Galactic disk. Variants of this reference model can serve as basis for future studies of diffuse emission in and outside the Galactic disk.

arXiv comment45 pages, 31 figures. Version 2 updated to match published version

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Cited by in corpus (36)

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• The Fermi-LAT GeV Excess Traces Stellar Mass in the Galactic Bulge
• Dark Matter Strikes Back at the Galactic Center
• Foreground Mismodeling and the Point Source Explanation of the Fermi Galactic Center Excess
• Prospects for Heavy WIMP Dark Matter with CTA: the Wino and Higgsino
• 3D template-based $Fermi$-LAT constraints on the diffuse supernova axion-like particle background
• Gamma rays as probes of cosmic-ray propagation and interactions in galaxies
• A Search for Dark Matter Annihilation in the Milky Way Halo
• Galactic Binaries Can Explain the Fermi Galactic Center Excess and 511 keV Emission
• Dissecting the inner Galaxy with $\gamma$-ray pixel count statistics
• Les Houches Lectures on Indirect Detection of Dark Matter
• When models fail: an introduction to posterior predictive checks and model misspecification in gravitational-wave astronomy
• Analyzing γ-rays of the Galactic Center with Deep Learning
• On the progressive hardening of the cosmic-ray proton spectrum in the inner Galaxy
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• Maximum Entropy Estimation of the Galactic Bulge Morphology via the VVV Red Clump
• Indirect searches for dark matter bound state formation and level transitions
• Toward the ultimate reach of current imaging atmospheric Cherenkov telescopes and their sensitivity to TeV dark matter
• Cherenkov Telescope Array sensitivity to the putative millisecond pulsar population responsible for the Galactic center excess
• Robust inference of the Galactic centre gamma-ray excess spatial properties
• A Phantom Menace: On the Morphology of the Galactic Center Excess
• Implications on Spatial Models of Interstellar Gamma-Ray Inverse-Compton Emission from Synchrotron Emission Studies in Radio and Microwaves
• Inverse Compton emission from millisecond pulsars in the Galactic bulge
• What the Milky Way's Dwarfs tell us about the Galactic Center extended excess
• Gamma-ray image reconstruction of the Andromeda galaxy
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• The Andromeda Gamma-Ray Excess: Background Systematics of the Millisecond Pulsars and Dark Matter Interpretations
• Harnessing the Population Statistics of Subhalos to Search for Annihilating Dark Matter
• Multi-Component Imaging of the Fermi Gamma-ray Sky in the Spatio-spectral Domain
• Non-Parametric Density Reconstruction of the Galactic Bulge Area using Red Clump Stars in the VVV Survey
• Applying Simulation-Based Inference to Spectral and Spatial Information from the Galactic Center Gamma-Ray Excess
• How do the dynamics of the Milky Way -- Large Magellanic Cloud system affect gamma-ray constraints on particle dark matter?
• On the Gravitational Wave Counterpart to a Gamma-ray Galactic Center Signal from Millisecond Pulsars
• Extended Higgs-portal dark matter and the Fermi-LAT Galactic Center Excess
• On the Energy Distribution of the Galactic Center Excess' Sources