Contribution of Gamma-Ray-loud Radio Galaxies' Core Emissions to the Cosmic MeV and GeV Gamma-Ray Background Radiation
Abstract
The Fermi gamma-ray satellite has recently detected gamma-ray emissions from radio galaxy cores. From these samples, we first examine the correlation between the luminosities at 5 GHz, L 5 GHz, and at 0.1-10 GeV, L γ, of gamma-ray-loud radio galaxies. We find that the correlation is significant with L γvpropL 1.16 5 GHz based on a partial correlation analysis. Using this correlation and the radio luminosity function (RLF) of radio galaxies, we explore the contribution of gamma-ray-loud radio galaxies to the unresolved extragalactic gamma-ray background (EGRB). The gamma-ray luminosity function is obtained by normalizing the RLF to reproduce the source-count distribution of the Fermi gamma-ray-loud radio galaxies. We find that gamma-ray-loud radio galaxies can explain ~25% of the unresolved Fermi EGRB flux above 100 MeV and will also make a significant contribution to the EGRB in the 1-30 MeV energy band. Since blazars explain 22% of the EGRB above 100 MeV, radio-loud active galactic nucleus populations explain ~47% of the unresolved EGRB. We further make an interpretation on the origin of the EGRB. The observed EGRB spectrum at 0.2-100 GeV does not show an absorption signature by the extragalactic background light. Thus, the dominant population of the origin of EGRB at very high energy (>30 GeV) might be either nearby gamma-ray-emitting sources or sources with very hard gamma-ray spectra.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2011
- DOI:
- 10.1088/0004-637X/733/1/66
- arXiv:
- arXiv:1103.3946
- Bibcode:
- 2011ApJ...733...66I
- Keywords:
-
- diffuse radiation;
- galaxies: active;
- gamma rays: diffuse background;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 9 pages, accepted for publication in ApJ