Paper detail

The extragalactic background light from the measurements of the attenuation of high-energy gamma-ray spectrum

The attenuation of high-energy gamma-ray spectrum due to the electron-positron pair production against the extragalactic background light (EBL) provides an indirect method to measure the EBL of the universe. We use the measurements of the absorption features of the gamma-rays from blazars as seen by Fermi Gamma-ray Space Telescope to explore the EBL flux density and constrain the EBL spectrum, star formation rate density (SFRD) and photon escape fraction from galaxies out to z=6. Our results are basically consistent with the existing determinations of the quantities. We find a larger photon escape fraction at high redshifts, especially at z=3, compared to the result from the recent Ly-alpha measurements. Our SFRD result is consistent with the data from both gamma-ray burst and UV observations in 1-sigma level. However, the average SFRD we obtain at z>~3 matches the gamma-ray data better than the UV data. Thus our SFRD result at z>~6 favors that it is sufficiently high enough to reionize the universe.