Measuring Omega Baryon from the Helium Lyman-Alpha Forest
Abstract
A new method to extract Omegab from high redshift intergalactic absorption is described, based on the distribution of HeII Ly-alpha optical depths in the voids in the ionization zone of quasars. A preliminary estimate from recent HST-STIS spectra of PKS 1935-692 at z=3 gives Omegab h2 = 0.013+0.002-0.001 (1-sigma statistical errors, for a Lambda-CDM cosmology with additional systematic uncertainties) consistent with other estimates.
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