First stars and the extragalactic background light: How recent γ-ray observations constrain the early universe

Details First stars and the extragalactic background light: How recent γ-ray observations constrain the early universe First stars and the extragalactic background light: How recent γ-ray observations constrain the early universe

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aipc.1085..490r&link_type=abstract

HIGH ENERGY GAMMA-RAY ASTRONOMY: Proceedings of the 4th International Meeting on High Energy Gamma-Ray Astronomy. AIP Conferenc

Astronomy and Astrophysics

Astronomy

Quasars, Active Or Peculiar Galaxies, Objects, And Systems, Gamma-Ray, Cosmology

Scientific paper

The end of the dark-ages of the universe-the epoch of reionization-is a one of the big open questions in cosmology. The first stars are commonly believed to be responsible for the reionization of the universe. They form in a pristine environment in clouds with zero (primordial) metallicity, where the cooling is dominated by H2 or H cooling. The first stars are hotter and (probably) more massive than the second generation stars, providing copious amounts of ionizing photons. Their formation has been extensively studied via numerical simulations, but a direct detection is still pending. Emission from the first stars is expected to contribute to the extragalactic background light (EBL) density in the optical to near-infrared wavelength region, possibly creating a unique spectral signature in the EBL. While difficult to access via direct measurements, lower limits on the optical to near-infrared EBL are derived from deep source counts. Recently, strong constraints on the EBL in near-infrared have been derived utilizing measured very high energy spectra together with assumptions about the source physics. These limits are compared with model calculations for the EBL resulting from the first stars. The model traces the evolving emissivity of an aging stellar population and takes into account the nebula emission from the dense clouds surrounding the sites of the first star formation. Different parameters of the first stars (star formation rate, stellar initial mass function, metallicity) are probed and limits on these parameters are presented.

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