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

Abstract

In this study, we systematically studied the X-ray to GeV gamma-ray spectra of 61 Fermi Large Area Telescope detected radio galaxies. We found an anticorrelation between peak frequency and peak luminosity in the high-energy spectral component of radio galaxies, similar to blazars. With this sample, we also constructed a gamma-ray luminosity function (GLF) of gamma-ray-loud radio galaxies. We found that blazar-like GLF shapes can reproduce their redshift and luminosity distribution, but the log N–log S relation prefers models with more low-z radio galaxies. Utilizing our latest GLF, the contribution of radio galaxies to the extragalactic gamma-ray background is found to be 1%–10%. We further investigated the nature of gamma-ray-loud radio galaxies. Compared to radio or X-ray flux-limited radio galaxy samples, the gamma-ray-selected sample tends to lack high radio power galaxies like FR II radio galaxies. We also found that only ∼10% of radio galaxies are GeV gamma-ray loud. Radio galaxies may contribute to the cosmic MeV gamma-ray background comparable to blazars if gamma-ray-quiet radio galaxies have X-ray to gamma-ray spectra like Cen A, with a small gamma-ray-to-X-ray flux ratio.

The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope: Data Release 3

“…FSRQs preferentially exhibit E pk IC below 1 GeV, while most BL Lac objects have E pk IC above this value, reflecting the dichotomy seen in the photon-index distributions (Figure 1). Most values of E pk IC obtained for the nine radio galaxies meeting the above condition are notably larger than those reported from a combined fit to the X-ray and gamma-ray data (see, e.g., Fukazawa et al 2022). An explanation for this discrepancy can be the presence of a prominent emission from the corona/accretion disk in the X-ray to soft gamma-ray bands, which drives down the fitted E pk IC value in the latter case.…”

Constraining the sources of ultra-high-energy cosmic rays across and above the ankle with the spectrum and composition data measured at the Pierre Auger Observatory

“…The case of no-evolution (m = 0) can be instead associated to the stellar-mass density [99], non-jetted AGN (low-luminosity Seyfert galaxies observed in X-rays [98]) and jetted AGN (intermediate-luminosity BL Lacs and FSRQs [97]). Negative evolutions (m = −3) can trace jetted AGN (low-luminosity BL Lacs observed in gamma rays [97]) or non-jetted AGN (radio-galaxies observed in gamma rays [100]), as well as the evolution with redshift of tidal disruption events (TDEs) [101]. At higher redshifts (z 1), the evolution of some of these classes of sources is uncertain.…”

ALMA Confirmation of Millimeter Time Variability in the Gamma-Ray Detected Seyfert Galaxy GRS 1734-292

“…It does not adhere to the established correlation between infrared and gamma-ray luminosity observed in starburst galaxies, thus ruling out starburst activity as the primary source (Ajello et al 2020). GRS 1734-292 also does not align the known correlation between the centimeter and gamma-ray luminosity of radio galaxies (Inoue 2011;Fukazawa et al 2022). Indeed, GRS 1734-292 exhibits a very bright gamma-ray luminosity compared to its 1.4 GHz radio flux of 63 mJy, which corresponds to a radio luminosity of L 1.4GHz = 7 × 10 22 W Hz −1 Marti et al (1998).…”

“…The Fermi Gamma-ray Space Telescope has cataloged 6658 gamma-ray objects thus far (Abdollahi et al 2022). Although blazars make up the majority of these detections, Fermi has also unveiled new gamma-ray emitting populations, including starburst galaxies and radio galaxies (Acciari et al 2019;Fukazawa et al 2022). Intriguingly, recent observations (Ackermann et al 2012;Wojaczyński et al 2015) have shown that gamma rays have been detected not only in starburst galaxies and radio galaxies but also in unjetted active galactic nuclei (AGNs) known as radio-quiet Seyfert galaxies (Seyfert 1943; Khachikian & Weedman 1974;Hills 1975).…”