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Very high energy (VHE, energy >= 100 GeV) γ-rays from cosmological sources are attenuated due to the interaction with photons of the extragalactic background light (EBL) in the ultraviolet to infrared wavelength bands. The EBL, thus, leaves an imprint on the observed energy spectra of these objects. In the last four years, the number of extragalactic VHE sources discovered with imaging atmospheric Cherenkov telescopes (IACTs), such as MAGIC, H.E.S.S., and VERITAS, has doubled. Furthermore, the measurements with the Fermi satellite brought new insights into the intrinsic spectra of the sources at GeV energies. Here, we present upper limits on the EBL intensity that are derived by considering the most extensive VHE source sample ever used in this context. This is accomplished by constructing a large number of generic EBL shapes and combining spectral information from Fermi and IACTs together with minimal assumptions about the source physics at high and very high gamma-ray energies. In addition to previous studies, the evolution of the EBL with redshift is accounted for and the possibility of the formation of an electromagnetic cascade and the implications on the upper limits are explored. The EBL density at z = 0 is constrained over more than two orders of magnitude in wavelength, i.e., between 0.4 and 100 μm. The resulting upper limits constitute the strongest ever reported over such a broad wavelength range. [ABSTRACT FROM AUTHOR]

γ-rays undergo pair production with photons of the extragalactic background light (EBL) in the ultra-violet to infrared wavelength band and, thus, the intrinsic photon flux is attenuated. For sources at cosmological distances, the absorption can be significant above 10 GeV, i.e., within the energy range of the large area telescope (LAT) on board the Fermi satellite. Here, photons in the first 39 months of Fermi-LAT data are analyzed which are associated with extragalactic sources with known redshift. Under the assumption of different EBL models, the expected number of photons is compared with the observed number at large optical depth. The background of unassociated photons is self-consistently derived from the Fermi-LAT data. As a result, the predictions for three recent EBL models are in conflict with the data at a 3 to 4σ level, which indicates a lower opacity of the Universe for high energy γ-rays than previously thought. [ABSTRACT FROM AUTHOR]

The cosmic star formation rate density (SFRD) is one of the fundamental quantities of cosmology. The SFRD is intimately connected with the extragalactic background light (EBL), i.e., the diffuse meta-galactic photon field in the ultraviolet to infrared, which is dominated by the emission from stars in galaxies. Directly measuring the EBL is difficult due to dominant foreground emission in our solar system and galaxy. However, stringent upper limits on its density are derived from observations of distant sources of very high energy (VHE; E>100 GeV) gamma-rays. Here, recent strong limits on the EBL density are used derive constraints on the SFRD. The stellar EBL contribution is modeled using detailed spectra from simple stellar population modeling. Dust attenuation and re-emission are included. A wide range of values for the different model parameters is investigated and their impact on the resulting EBL is studied. The EBL modeling is then compared with EBL constraints to derive limits on the SFRD. Here, results from this study are reported and implications for the SFRD are discussed. [ABSTRACT FROM AUTHOR]