Modeling the Extragalactic Background Light From Stars and Dust

Abstract

The extragalactic background light (EBL) from the far infrared through the visible and extending into the ultraviolet is thought to be dominated by starlight, either through direct emission or through absorption and reradiation by dust. This is the most important energy range for absorbing γ-rays from distant sources such as blazars and gamma-ray bursts and producing electron-positron pairs. In previous work we presented EBL models in the optical through ultraviolet by consistently taking into account the star formation rate (SFR), initial mass function (IMF) and dust extinction, and treating stars on the main sequence as blackbodies. This technique is extended to include post-main sequence stars and reprocessing of starlight by dust. In our simple model, the total energy absorbed by dust is assumed to be re-emitted as three blackbodies in the infrared, one at 40 K representing warm, large dust grains, one at 70 K representing hot, small dust grains, and one at 450 K representing polycyclic aromatic hydrocarbons. We find our best fit model combining the Hopkins and Beacom SFR using the Cole et al. parameterization with the Baldry and Glazebrook IMF agrees with available luminosity density data at a variety of redshifts. Our resulting EBL energy density is quite close to the lower limits from galaxy counts and in some cases below the lower limits, and agrees fairly well with other recent EBL models shortward of about 5 µm. Deabsorbing TeV γ-ray spectra of various blazars with our EBL model gives results consistent with simple shock acceleration theory. We also find that the universe should be optically thin to γ-rays with energies less than 20 GeV.

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.…”

Effects of spatial fluctuations in the extragalactic background light on hard gamma-ray spectra

“…Based on the cross section of the photon-photon inter- Razzaque et al (2009). The emission of the dust component, responsible for the two peaks at λ 8µm, is computed following Finke et al (2010). action and a model of the EBL density the optical depth (τ ) can be computed for VHE γ-ray sources at redshift z.…”