Journal
ASTROPHYSICAL JOURNAL
Volume 733, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/733/1/66
Keywords
diffuse radiation; galaxies: active; gamma rays: diffuse background
Categories
Funding
- Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan [19047003, 19740099]
- Japan Society for the Promotion of Science (JSPS)
- Grants-in-Aid for Scientific Research [19740099, 09J00878] Funding Source: KAKEN
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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-gamma, of gamma-ray-loud radio galaxies. We find that the correlation is significant with L-gamma alpha L-5 GHz(1.16) 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 similar to 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 similar to 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.
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