2002/07/11 by Vasiliki Pavlidou, Brian D. Fields · 2 citations
Physics and Astronomy · #Active galactic nucleus #Astrophysics and Cosmic Phenomena #Dark Matter and Cosmic Phenomena #Flux (metallurgy) #Galaxy #Interstellar medium #Neutrino Physics Research #Spectral line #Star formation #Stars #Supernova #astro-ph #hep-ph
paper · pdf · doi:10.1086/342670
published as Astrophys.J. 575 (2002) L5-L8 · 11 pages, 1 figure, uses AASTeX. To appear in ApJL
arxiv created 2002/07/11 · openalex publication_date 2002/08/10 · arxiv updated 2009/11/30 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The diffuse extragalactic gamma-ray background (EGRB) above 100 MeV encodes unique information about high-energy processes in the universe. Numerous sources for the EGRB have been proposed, but the two systems that are certain to make some contribution are active galaxies (blazars) as well as normal galaxies. In this Letter we evaluate the contribution to the background from both sources. The active galaxy contribution arises from unresolved blazars. We compute this contribution using the Stecker-Salamon model. For normal galaxies, the emission is due to cosmic-ray interactions with diffuse gas. Our key assumption here is that the cosmic-ray flux in a galaxy is proportional to the supernova rate and thus the massive star formation rate, quantified observationally by the cosmic star formation rate (CSFR). In addition, the existence of stars today requires a considerably higher interstellar medium mass in the past. Using the CSFR to compute both these effects, we find that normal galaxies are responsible for a significant portion (~ ) of the EGRB near 1 GeV but make a smaller contribution at other energies. Finally, we present a "minimal" two-component model that includes contributions from both normal galaxies and blazars. We show that the spectrum of the diffuse radiation is a key constraint on this model: while neither the blazar spectra nor the galactic spectra are separately optimal fits to the observed spectrum, the combined emission provides an excellent fit. We close by noting key observational tests of this two-component model, which can be probed by future gamma-ray observatories, such as the Gamma-ray Large Area Space Telescope .