Improved Modeling of the Discrete Component of the Galactic Interstellar Gamma-ray Emission and Implications for the Fermi-LAT Galactic Center Excess

The aim of this work is to improve models for the γ -ray discrete or small-scale structure related to H 2 interstellar gas. Reliably identifying this contribution is important to disentangle γ -ray point sources from interstellar gas, and to better characterize extended γ -ray signals. Notably, the Fermi – LAT Galactic center (GC) excess, whose origin remains unclear, might be smooth or point-like. If the data contain a point-like contribution that is not adequately modeled, a smooth GC excess might be erroneously deemed to be point-like. We improve models for the H 2 -related γ -ray discrete emission for a 50 ◦ × 1 ◦ region along the Galactic plane via H 2 proxies better suited to trace these features. We find that these are likely to contribute significantly to the γ -ray Fermi –LAT data in this region, and the brightest ones are likely associated with detected Fermi –LAT sources, a compelling validation of this methodology. We discuss prospects to extend this methodology to other regions of the sky and implications for the characterization of the GC excess.

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