The $\gamma$-ray Milky Way above 10 GeV: Distinguishing Sources from Diffuse Emission

TL;DR

This paper introduces a new image-analysis method to distinguish between point source and diffuse gamma-ray emissions in the Milky Way using Fermi-LAT data, improving understanding of their spatial distribution at energies above 10 GeV.

Contribution

A simple, effective image-analysis technique is developed to separate source and diffuse gamma-ray emissions in the Galactic plane, tested against models with known emission fractions.

Findings

Method successfully separates source and diffuse emissions.

Effective at energies from 10 GeV to 500 GeV.

Provides insights into the spatial distribution of gamma-ray sources.

Abstract

One of the most prominent features of the $\gamma$-ray sky is the emission from our own Galaxy. The Galactic plane has been observed by Fermi-LAT in GeV and H.E.S.S. in TeV light. Fermi has modeled the Galactic emission as the sum of a complex 'diffuse' emission model with the predominately point source catalogs of 1FHL and 2FGL, while H.E.S.S. has primarily detected extended TeV sources. At GeV energies, Galactic diffuse emission dominates the $\gamma$-ray Milky Way but, as sources have hard spectra, it is likely their emission dominates at TeV energies. Generally the spatial shape and fraction of source emission compared to diffuse emission in the Galactic plane is not well known and is dependent on the source detection method, threshold and diffuse emission modeling methods used. We present a simple image-analysis based method applied to Fermi-LAT data from 10 GeV to 500 GeV, covering a region of +/- 5 degrees in Galactic latitude and +/- 100 degrees in Galactic longitude, to separate source and diffuse emission. This method involves elongated filter smoothing, combined with significance clipping to exclude sources. We test the method against models based on the 1FHL catalog and very simple model Galaxies to evaluate the response for an input of known fraction and shape of diffuse and source emission.