Extragalactic background light

The understanding of the EBL is also fundamental for extragalactic very-high-energy (VHE, 30 GeV-30 TeV) astronomy. VHE photons coming from cosmological distances are attenuated by pair production with EBL photons. This interaction is dependent on the spectral energy distribution (SED) of the EBL. Therefore, it is necessary to know the SED of the EBL in order to study intrinsic properties of the emission in the VHE sources.

Observations

The direct measurement of the EBL is difficult mainly due to the contribution of zodiacal light that is orders of magnitude higher than the EBL. Different groups have claimed the detection of the EBL in the optical and near-infrared. However, it has been proposed that these analyses have been contaminated by zodiacal light. Recently, two independent groups using different technique have claimed the detection of the EBL in the optical with no contamination from zodiacal light.

There are also other techniques that set limits to the background. It is possible to set lower limits from deep galaxy surveys. On the other hand, VHE observations of extragalactic sources set upper limits to the EBL.

In November 2018, astronomers reported that the EBL amounted to 4 × 10⁸⁴ photons.