Extragalactic Background Light Inferred from AEGIS Galaxy SED-type Fractions

Abstract

The extragalactic background light (EBL) is of fundamental importance both for understanding the entire process of galaxy evolution and for γ-ray astronomy. However, the overall spectrum of the EBL between 0.1 and 1000 µm has never been determined directly neither from observed luminosity functions (LFs), over a wide redshift range, nor from any multiwavelength observation of galaxy spectral energy distributions (SEDs). The evolving, overall spectrum of the EBL is derived here utilizing a novel method based on observations only. The changing fractions of quiescent galaxies, star-forming galaxies, starburst galaxies and active galactic nucleus (AGN) galaxies from redshift 0.2 to 1 are estimated, and two alternative extrapolations of SED types to higher redshifts are considered. This allows calculation of the evolving EBL. The EBL uncertainties in our modelling based directly on the data are quantified, and their consequences for attenuation of very-high-energy γ-rays due to pair production on the EBL are discussed. It is concluded that the EBL seems well constrained from the UV to the mid-IR at an intensity level roughly matching galaxy count data. Independent efforts from IR and γ-ray astronomy are needed in order to reduce the uncertainties in the far-IR.

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.…”

Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory

“…The CMB has been extremely well characterized and has been shown to be a very isotropic pure black-body spectrum, at least to the accuracy relevant for UHECR propagation. The EBL, which comprises the radiation produced in the Universe since the formation of the first stars, is relatively less known: several models of EBL have been proposed [50][51][52][53][54][55][56], among which there are sizeable differences, especially in the far infrared and at high redshifts. Concerning the interactions of protons and nuclei in the extragalactic environment, the loss mechanisms and their relevance for the propagation were predicted by Greisen [7] and independently by Zatsepin and Kuzmin [8] soon after the discovery of the CMB.…”

“…Several approaches have been used to follow the interactions in the extragalactic environment, both analytically and using Monte Carlo codes. In this paper simulations based on CRPropa [13][14][15] and SimProp [16][17][18] will be used, along with the Gilmore [53] and Domínguez (fiducial) [54] models of EBL and the Puget, Stecker and Bredekamp (PSB) [58,59], TALYS [49,[60][61][62] and Geant4 [63] models of photo-disintegration in various combinations. A comparison between the Monte Carlo codes used here is beyond the scope of this paper, and has been discussed in [49].…”

“…To study the effects of uncertainties in the simulations of UHECR propagation, we repeated the fit using the combinations of Monte Carlo propagation code, photo-disintegration cross sections and EBL spectrum listed in table 7. In the present analysis EBL spectra and evolution are taken from [53] (Gilmore 2012) and [54] (Domínguez 2011). As for photodisintegration, here we use the cross sections from [50,51] (PSB), [61] (TALYS, as described in [49]), and Geant4 [63] total cross sections with TALYS branching ratios ( [49]).…”