Semi-analytic modelling of the extragalactic background light and consequences for extragalactic gamma-ray spectra

Abstract

Attenuation of high-energy gamma-rays by pair production with ultraviolet, optical and infrared (IR) extragalactic background light (EBL) photons provides a link between the history of galaxy formation and high-energy astrophysics. We present results from our latest semi-analytic models (SAMs), which employ the main ingredients thought to be important to galaxy formation and evolution, as well as an improved model for reprocessing of starlight by dust to mid- and far-IR wavelengths. These SAMs are based upon a Λ cold dark matter hierarchical structural formation scenario, and are successful in reproducing a large variety of observational constraints such as number counts, luminosity and mass functions and colour bimodality. Our fiducial model is based upon a Wilkinson Microwave Anisotropy Probe 5-year cosmology, and treats dust emission using empirical templates. This model predicts a background flux considerably lower than optical and near-IR measurements that rely on subtraction of zodiacal and galactic foregrounds, and near the lower bounds set by number counts of resolvable sources at a large number of wavelengths. We also show the results of varying cosmological parameters and dust attenuation model used in our SAM. For each EBL prediction, we show how the optical depth due to electron-positron pair production is affected by redshift and gamma-ray energy, and the effect of gamma-ray absorption on the spectra of a variety of extragalactic sources. We conclude with a discussion of the implications of our work, comparisons to other models and key measurements of the EBL and a discussion of how the burgeoning science of gamma-ray astronomy will continue to help constrain cosmology. The low EBL flux predicted by our fiducial model suggests an optimistic future for further studies of distant gamma-ray sources.Ministerio de Educación y Ciencia FIS2008-04189Fondo Europeo de Desarrollo Regional CSD2007-00042Junta de Andalucía P07-FQM-0289

EBL constraints using a sample of TeV gamma-ray emitters measured with the MAGIC telescopes

“…The method used is similar to [4,5] and [16]. The EBL model used here is from [12] and similar results are obtained when using models of [10,11] and [13]. Our result on the EBL scaling factor is α = 0.99(+0.10)(−0.12), statistical errors only and α = 0.99(+0.15)(−0.56) when adding systematic uncertainties.…”

“…The recent models of [10,11,12,13] can reproduce well the EBL spectrum seen at redshift z=0 and have in general good agreement among each other as well as with the indirect constraints and detections using VHE γ-ray sources. The latter suggests that there are not many unresolved sources of EBL out there.…”

NEW HIGH-z FERMI BL LACS WITH THE PHOTOMETRIC DROPOUT TECHNIQUE

“…Moreover, the properties of these objects are in agreement with the blazar sequence and wereexamined using the various parameters as illustrated in . Three of these new objects were reported in the 2FHL catalog, from which the highest energy photons (E>50 GeV) coupled with the redshift measurements were utilized to test the consistency with the currently known EBL models, e.g., Finke (2010), Domínguez et al (2011), andGilmore et al (2011. Detecting high-z BL Lacs with asubstantial amount of >50 GeV emission allowed us to constrain the EBL in a region where there are not, as yet, measurements of the optical depth.…”

Very high-energyγ-ray emission from high-redshift blazars

“…Gamma-ray emission from distant blazars is suppressed by the effect of pair production through interactions of these γ rays with the low-energy photons forming the extragalactic background light (EBL; Gould & Schreder 1967;Kneiske et al 2004;Stecker et al 2006;Mazin & Raue 2007;Franceschini et al 2008;Gilmore et al 2012). This prevents observations of highredshift sources using the technique of imaging the Cherenkov emission produced through γ-ray-induced air showers, used by the ground-based Cherenkov telescopes HESS, MAGIC, and VERITAS (Aharonian et al 2008).…”

“…Measurement of the effect of suppression of the VHE γ-ray flux from low-redshift blazars is commonly used for the estimation of the density of the EBL in the local Universe (Kneiske et al 2004;Stecker et al 2006;Mazin & Raue 2007;Franceschini et al 2008;Gilmore et al 2012). Constraints on the EBL density and spectral characteristics, extracted from the VHE blazar observations, are useful for understanding the cosmological evolution of galaxies.…”