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The Evolution of the Intergalactic Medium Transmission to Redshift Six

Antoinette Songaila
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Abstract

We have measured the transmission of the Lyman alpha forest produced by neutral hydrogen scattering in the intergalactic medium between redshifts 2 and 6.3 using high signal to noise, high resolution (R > 5000) observations of 50 quasars spread over the redshift range. We use a uniform set of 15 Angstrom intervals covering Lyman alpha, Lyman beta, and Lyman gamma absorption regions to tabulate the forest transmission as a function of redshift. The transmitted fractions show a relatively smooth evolution over the entire range of redshifts, which can be modelled with a smoothly decreasing ionization rate. Previous claims of an abrupt change at a redshift of approximately 6 appear in part to be a consequence of an incorrect conversion of Lyman beta to Lyman alpha optical depths. The tabulated transmissions can be used to calculate the colors of objects with a specified input spectrum as a function of redshift. We calculate the colors of a flat f_nu galaxy with a large intrinsic continuum break, as an important example.

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Antoinette Songaila. 2004-02-13. The Evolution of the Intergalactic Medium Transmission to Redshift Six. https://doi.org/10.1086/383561

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