Gamma-Rays from Star Forming Activity Appear to Outshine Misaligned Active Galactic Nuclei

Abstract

The total extragalactic γ-ray flux provides a powerful probe into the origin and evolution of the highest energy processes in our universe. An important component of this emission is the isotropic γ-ray background (IGRB), composed of sources that cannot be individually resolved by current experiments. Previous studies have determined that the IGRB can be dominated by either misaligned active galactic nuclei (mAGN) or star-forming galaxies (SFGs). However, these analyses are limited, because they have utilized binary source classifications and examined only one source class at a time. We perform the first combined joint-likelihood analysis that simultaneously correlates the γ-ray luminosity of extragalactic objects with both star-formation and mAGN activity. We find that SFGs produce 48 +33 −20 % of the total IGRB at 1 GeV and 56 +40 −23 % of the total IGRB at 10 GeV. The contribution of mAGN is more uncertain, but can also be significant. Future work to quantify the radio and infrared properties of nearby galaxies could significantly improve these constraints.

High-energy Emission Component, Population, and Contribution to the Extragalactic Gamma-Ray Background of Gamma-Ray-emitting Radio Galaxies

“…Various studies estimated the contribution of radio galaxies to the EGB (Inoue 2011;Di Mauro et al 2014;Hooper et al 2016;Stecker et al 2019;Blanco & Linden 2021). Inoue (2011) estimated this contribution by using radio galaxies in the 1FGL, 3FGL, FL8Y (a precursor to 4FGL), and 4FGL.…”

High-Energy Extragalactic Neutrino Astrophysics

“…This could be achieved by hypernovae or other energetic transients, stronger magnetic fields, galactic winds, and AGN embedded in highly star-forming galaxies (43,180,181,182,183). Recent studies have showed that star-forming galaxies give a significant contribution to the isotropic diffuse gamma-ray background (184,185). However, the contribution to the all-sky neutrino flux is likely to be subdominant at least below 100 TeV, although they can still make a sizable contribution above 100 TeV given that the cosmic-ray spectrum is harder than ∝ E −2.2 .…”

High energy emission component, population, and contribution to the extragalactic gamma-ray background of gamma-ray emitting radio galaxies

“…Various studies estimated the contribution of radio galaxies to the EGB (Inoue 2011;Di Mauro et al 2014;Hooper et al 2016;Stecker et al 2019;Blanco & Linden 2021). Inoue (2011) estimated this contribution by using radio galaxies in the 1FGL, 3FGL.…”