Gamma-ray sources at high latitudes (Extragalactic gamma-ray sources)

TL;DR

This review summarizes the properties, variability, and potential sources of high-latitude gamma-ray emissions, emphasizing active galactic nuclei and exploring other possible gamma-ray emitters for future observations.

Contribution

It provides a comprehensive overview of high-latitude gamma-ray sources, analyzing their statistical properties, variability, and potential origins, including new candidate sources for upcoming gamma-ray catalogs.

Findings

Active galactic nuclei dominate high-latitude gamma-ray sources.

Potential gamma-ray emitters include starburst galaxies, galaxy clusters, and molecular clouds.

Some unidentified sources may be related to nearby galaxies or other extragalactic objects.

Abstract

This Chapter provides a review of $\gamma$-ray sources lying at high Galactic latitudes. Their statistical properties and variability status, as well as studies involving cross correlations with lower frequency catalogs and multiwavelength observations, are summarized. The case for active galactic nuclei is analyzed with special emphasis, since they represent the largest population of high energy sources known to date. Other potential $\gamma$-ray emitters (including nearby starburst galaxies, normal galaxies, molecular clouds in the Galactic halo, galaxy clusters, and radio galaxies) that may appear in the next generation of $\gamma$-ray catalogs and, perhaps, that might have been already observed by EGRET as unidentified detections, are discussed.