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

TL;DR

This paper enhances models of small-scale gamma-ray emission linked to interstellar H2 gas to better distinguish point sources from diffuse signals, impacting the understanding of the Galactic Center excess.

Contribution

It introduces improved H2 proxies for modeling gamma-ray discrete emission, aiding in more accurate separation of point sources and diffuse signals in Fermi-LAT data.

Findings

H2-related gamma-ray emission significantly contributes to the observed data.

Brightest gamma-ray features are associated with known Fermi-LAT sources.

Methodology validated by successful identification of known sources.

Abstract

The aim of this work is to improve models for the gamma-ray discrete or small-scale structure related to H2 interstellar gas. Reliably identifying this contribution is important to disentangle gamma-ray point sources from interstellar gas, and to better characterize extended gamma-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 H2-related gamma-ray discrete emission for a $50^\circ \times 1^\circ$ region along the Galactic plane via H2 proxies better suited to trace these features. We find that these are likely to contribute significantly to the gamma-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.