Extragalactic optical-infrared background radiation, its time evolution and the cosmic photon-photon opacity

By A. Franceschini, G. Rodighiero, Mattia Vaccari Astronomy Department, U. Padova. 2008

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Context. The background radiation in the optical and the infrared cause energy loss in the propagation of high energy particles through space. In particular, TeV observations with Cherenkov telescopes of extragalactic sources are influenced by the opacity effects due to the interaction of the very high-energy source photons with the background light. Aims. With the aim of assessing with the best possible detail these opacity terms, we have modelled the extragalactic optical and infrared backgounds using available information on cosmic sources in the universe from far-UV to sub-millimeter wavelengths over a wide range of cosmic epochs. Methods. We have exploited the relevant cosmological survey data – including number counts, redshift distributions, luminosity functions – from ground-based observatories in the optical, near-IR, and sub-millimeter, as well as multi-wavelength information coming from the HST, ISO and Spitzer space telescopes. Additional constraints have been used from direct measurements or upper limits on the extragalactic backgrounds by dedicated missions (COBE). All data were fitted and interpolated with a multi-wavelength backward evolutionary model, allowing us to estimate the background photon density and its redshift evolution. From the redshift-dependent background spectrum, the photon-photon opacities for sources of high-energy emission at any redshifts were then computed. The same results can also be used to compute the optical depths for any kind of processes in the intergalactic space involving interactions with background photons (like scattering of cosmic-ray particles). Results. We have applied our photon-photon opacity estimates to the analysis of spectral data at TeV energies on a few BLAZARs of particular interest. The opacity-corrected TeV spectra are entirely consistent with standard photon-generation processes and show photon indices steeper than Γintrinsic = 1.6. Contrary to some previous claims, but in agreement with other reports, we find no evidence for any truly diffuse background components in addition to those from resolved sources. We have tested in particular the effects of a photon background originating at very high redshifts, as would be the emissions by a primeval population of Population III stars around z ∼ 10. We could not identify any opacity features in our studied BLAZAR spectra consistent with such an emission and place a stringent limit on such a diffuse photon intensity of ∼ 6n W/m 2 /sr between 1 and 4 μm. Conclusions. TeV observations of BLAZARs are consistent with background radiation contributed by resolved galaxies in the optical and IR, and exclude prominent additional components from very high-z unresolved sources.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/19a65bf30931b2dccf9b79289b21c640dffdb3bf

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Citations in the corpus

EGMF Constraints from Simultaneous GeV-TeV Observations of Blazars (2011, methodology): “For these results and the results throughout this paper, the EBL model of Franceschini et al. (2008) is adopted, in which the evolution of the EBL with redshift is accounted for.”
THE EXTRAGALACTIC BACKGROUND LIGHT, THE HUBBLE CONSTANT, AND ANOMALIES: CONCLUSIONS FROM 20 YEARS OF TeV GAMMA-RAY OBSERVATIONS (2015, methodology): “A.1 EBL Evolution We compare, in Figure 11, gamma-ray optical depths published by Franceschini et al. (2008) and Gilmore et al. (2012) with optical depths derived from Equation (9), assuming the z = 0 specific intensities as given in each paper with a template evolution with f 1.7.evol = The…”
Semi-analytic modelling of the extragalactic background light and consequences for extragalactic gamma-ray spectra: Modelling of the EBL and gamma-ray spectra (2012, methodology): “…of a fairly low extragalactic background across the optical and near- to mid-IR, supported by convergence with alternative methods such as Franceschini et al. (2008) and D11 as well as new direct measurement techniques and recent limits from gamma-ray experiments in the optical to…”
A lower-limit flux for the extragalactic background light (2010, background): “…wavelength range (for the most recent ones: Chary & Elbaz 2001; Malkan & Stecker 2001; Totani & Takeuchi 2002; Lagache et al., 2003, 2004; Xu et al., 2003; King et al., 2003, Stecker et al., Send offprint requests to: T.M. Kneiske e-mail:tanja.kneiske@desy.de 2006; Franceschini et al., 2008).”
A hadronic origin for ultra-high-frequency-peaked BL Lac objects (2014, methodology): “• The absorption by the EBL is computed using the model by Franceschini et al. (2008), which agrees well with the latest constraints obtained by very-high-energy (VHE; E>100 GeV) observations (Aharonian et al. 2006; H.E.S.S. Collaboration et al. 2013).”
Mid- and far-infrared luminosity functions and galaxy evolution from multiwavelength Spitzer observations up to z ~ 2.5 (2009, result): “Also in comparison with model predictions by Franceschini et al. (2009, in preparation, but see also Franceschini et al. 2008), our results confirm the presence of a very rapid increase of the galaxy IR volume emissivity up toz ∼ 1 and the evidence for the existence of a population of very luminous…”
CONTRIBUTION OF GAMMA-RAY-LOUD RADIO GALAXIES’ CORE EMISSIONS TO THE COSMIC MeV AND GeV GAMMA-RAY BACKGROUND RADIATION (2011, background): “Here ω(Fγ [Lγ , z]) is the detection efficiency of Fermi at the photon flux Fγ , which corresponds to the flux from a source with a gamma-ray luminosity Lγ at redshift z. High-energy γ -rays ( 20 GeV) propagating through the universe are absorbed by the interaction with the extragalactic background ”
Extreme TeV blazars and the intergalactic magnetic field (2010, result): “In the range of wavelength interesting here,0.1 − 15 µm, several of recent EBL estimates converge: the recent models f Franceschini et al. (2008), Gilmore et al. (2009), Finke et al. (2010), Dominguez et al. (2010), agree well (but see Orr et al. 2011) and are consistent with the low level of the…”
Star-forming galaxies as the origin of diffuse high-energy backgrounds: gamma-ray and neutrino connections, and implications for starburst history (2014, methodology): “The remaining discrepancy of ∼ 2 can be explained by the fact that the EBL model [67] used in Ref.”
MODELING THE EXTRAGALACTIC BACKGROUND LIGHT FROM STARS AND DUST (2009, methodology): “Franceschini et al. (2008) consider the latter to be more likely, based on the fact that the galaxy counts are performed in fields with quite deep exposures.”
Measurement of the extragalactic background light imprint on the spectra of the brightest blazars observed with H.E.S.S. (2012, methodology): “The template chosen for the EBL density n is the model of Franceschini et al. (2008), hereafter FR08, which is representative of the current state of the art of EBL modelling and for which the optical depth is finely discretized in energy and redshift1.”