The stellar contribution to the extra-galactic background light and absorption of high-energy gamma-rays

TL;DR

This paper models the stellar contribution to the extragalactic background light (EBL) using galaxy data and star formation history, and assesses its impact on high-energy gamma-ray absorption.

Contribution

It introduces a new EBL model based on stellar initial mass functions and star formation history, fitting observational data and calculating gamma-ray absorption implications.

Findings

Best-fit models use modified Salpeter A IMF with specific star formation histories.

Calculated EBL models serve as lower limits in the 0.1-1 eV range.

Results inform gamma-ray observations by Fermi and Cherenkov telescopes.

Abstract

TeV gamma rays from distant astrophysical sources are attenuated due to electron-positron pair creation by interacting with ultraviolet/optical to infrared photons which fill the universe and are collectively known as the extra-galactic background light (EBL). We model the ~0.1-10 eV starlight component of the EBL derived from expressions for the stellar initial mass function, star formation history of the universe, and wavelength-dependent absorption of a large sample of galaxies in the local universe. These models are simultaneously fitted to the EBL data as well as to the data on the stellar luminosity density in our local universe. We find that the models with modified Salpeter A initial mass function together with Cole et al. (2001) or Hopkins and Beacom (2006) star formation history best represent available data. Since no dust emission is included, our calculated EBL models can be interpreted as the lower limits in the ~0.1-1 eV range. We present simple analytic fits to the best-fit EBL model evolving with redshift. We then proceed to calculate gamma-ray opacities, and absorption of ~10-300 GeV gamma-rays coming from different redshifts. We discuss implications of our results for the Fermi Gamma Ray Space Telescope and ground-based Air Cherenkov Telescopes.