Modeling the Extragalactic Background Light and the Cosmic Star Formation History

Abstract

We present an updated model for the extragalactic background light (EBL) from stars and dust, over wavelengths ≈ 0.1 µm to 1000 µm. This model uses accurate theoretical stellar spectra, and tracks the evolution of star formation, stellar mass density, metallicity, and interstellar dust extinction and emission in the universe with redshift. Dust emission components are treated self-consistently, with stellar light absorbed by dust reradiated in the infrared as three blackbody components. We fit our model, with free parameters associated with star formation rate and dust extinction and emission, to a wide variety of data: luminosity density, stellar mass density, and dust extinction data from galaxy surveys; and γ-ray absorption optical depth data from γ-ray telescopes. Our results strongly constraint the star formation rate density and dust photon escape fraction of the universe out to redshift z = 10, about 90% of the history of the universe. We find our model result is, in some cases, below lower limits on the z = 0 EBL intensity, and below some low-z γ-ray absorption measurements. Subject headings: diffuse radiation-gamma rays-gamma-ray sources-gamma-ray astronomyblazars producing electron-positron pairs and absorbing the γ-ray photon (e.g., Gould & Schréder 1967b). The cross section for this process is strongly peaked at an energy about a factor of 2 greater than the energy in Equation (1). In recent years, this has led to a number of attempts to measure the EBL with extragalactic γ-ray sources, primarily blazars, and a number of modeling efforts. Constraints on the EBL with γ rays have been found with ground-based imaging atmospheric telescopes (IACTs) such as MAGIC, H.E.S.S., and VERITAS; and with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space