A luminosity constraint on the origin of unidentified high energy sources

TL;DR

This paper introduces a luminosity constraint method using M31 as a Milky Way proxy to evaluate the Galactic origin of unidentified high-energy sources, providing a new tool to distinguish between Galactic and extragalactic populations.

Contribution

The authors propose a novel luminosity constraint approach that assesses the likelihood of Galactic origin for high-energy sources based on galaxy similarities, complementing existing identification methods.

Findings

Unlikely that most unidentified sources are Galactic halo objects.

Current data cannot exclude all sources being Galactic if in disk/bulge.

Method can be applied to future Fermi data to exclude more Galactic associations.

Abstract

The identification of point sources poses a great challenge for the high energy community. We present a new approach to evaluate the likelihood of a set of sources being a Galactic population based on the simple assumption that galaxies similar to the Milky Way host comparable populations of gamma-ray emitters. We propose a luminosity constraint on Galactic source populations which complements existing approaches by constraining the abundance and spatial distribution of any objects of Galactic origin, rather than focusing on the properties of a specific candidate emitter. We use M31 as a proxy for the Milky Way, and demonstrate this technique by applying it to the unidentified EGRET sources. We find that it is highly improbable that the majority of the unidentified EGRET sources are members of a Galactic halo population (e.g., dark matter subhalos), but that current observations do not provide any constraints on all of these sources being Galactic objects if they reside entirely in the disk and bulge. Applying this method to upcoming observations by the Fermi Gamma-ray Space Telescope has the potential to exclude association of an even larger number of unidentified sources with any Galactic source class.