Published in Physics Reports, Volume 598, p. 1-58, 2015.
For a PDF version of the article, click here.
https://arxiv.org/abs/1502.02866
Abstract: We review the current understanding of the diffuse gamma-ray background (DGRB). The DGRB is what remains of the total measured gamma-ray emission after the subtraction of the resolved sources and of the diffuse Galactic foregrounds. It is interpreted as the cumulative emission of sources that are not bright enough to be detected individually. Yet, its exact composition remains unveiled. Well-established astrophysical source populations (e.g. blazars, misaligned AGNs, star-forming galaxies and millisecond pulsars) all represent guaranteed contributors to the DGRB. More exotic scenarios, such as dark matter annihilation or decay, may contribute as well. In this review, we describe how these components have been modeled in the literature and how the DGRB can be used to provide valuable information on each of them. We summarize the observational information currently available on the DGRB, paying particular attention to the most recent measurement of its intensity energy spectrum by the Fermi LAT Collaboration. We also discuss the novel analyses of the auto-correlation angular power spectrum of the DGRB and of its cross-correlation with tracers of the large-scale structure of the Universe. New data sets already (or soon) available are expected to provide further insight on the nature of this emission. By summarizing where we stand on the current knowledge of the DGRB, this review is intended both as a useful reference for those interested in the topic and as a means to trigger new ideas for further research.
Table of Contents
Table of acronyms
| 1FGL | Fermi LAT First Source Catalog |
| 2FGL | Fermi LAT Second Source Catalog |
| 2FPC | Fermi LAT Second Catalog of gamma-ray pulsars |
| 2LAC | Fermi LAT Second Catalog of Active Galactic Nuclei |
| 2MASS | 2 Micron All-Sky Survey |
| 3FGL | Fermi LAT Third Source Catalog |
| AGN | Active Galactic Nucleus |
| APS | Angular Power Spectrum |
| CFHTLenS | Canada-France-Hawaii Telescope Lensing Survey |
| CMB | Cosmic Microwave Background |
| CR | Cosmic Ray |
| CTA | Cherenkov Telescope Array |
| DES | Dark Energy Survey |
| DESI | Dark Energy Spectroscopic Instrument |
| DGRB | Diffuse Gamma-Ray Background |
| DM | Dark Matter |
| eBOSS | extended Baryon Oscillation Spectroscopy Survey |
| EBL | Extragalactic Background Light |
| FRI | Fanaroff-Riley Class I |
| FRII | Fanaroff-Riley Class II |
| FSRQ | Flat-Spectrum Radio Quasar |
| HMF | Halo Mass Function |
| HOD | Halo Occupation Distribution |
| HSP | High-Synchrotron Peak |
| IC | Inverse Compton |
| IR | InfraRed |
| ISP | Intermediate-Synchrotron Peak |
| JWST | James Webb Space Telescope |
| LF | Luminosity Function |
| LOFAR | Low-Frequency Array |
| LSP | Low-Synchrotron Peak |
| LSS | Large-Scale Structure |
| MAGN | Misaligned Active Galactic Nucleus |
| MSP | MilliSecond Pulsar |
| MW | Milky Way |
| NFW | Navarro-Frenk-White |
| NuSTAR | Nuclear Spectroscopic Telescope Array |
| NVSS | NRAO VLA Sky Survey |
| Probability Distribution Function | |
| PSF | Point Spread Function |
| SDSS | Sloan Digital Sky Survey |
| SED | Spectral Energy Distribution |
| SFG | Star-Forming Galaxy |
| SFR | Star-Forming Rate |
| SKA | Square Kilometer Array |
| UHECR | Ultra-High-Energy Cosmic Ray |
| UV | UltraViolet |
| WIMP | Weakly Interacting Massive Particle |
| WISE | Wide-field Infrared Survey Explorer |
| WMAP | Wilkinson Microwave Anisotropy Probe |