Resolving the Structure of Ionized Helium in the Intergalactic Medium with the Far Ultraviolet Spectroscopic Explorer

Preprint

9 August 2001

preprint
Published by arXiv in arXiv

https://doi.org/10.48550/arXiv.astro-ph/0108169

Abstract

The neutral hydrogen and the ionized helium absorption in the spectra of quasars are unique probes of structure in the early universe. We present Far-Ultraviolet Spectroscopic Explorer observations of the line of sight to the quasar HE2347-4342 in the 1000-1187 A band at a resolving power of 15,000. We resolve the He II Ly alpha absorption as a discrete forest of absorption lines in the redshift range 2.3 to 2.7. About 50 percent of these features have H I counterparts with column densities log N(HI) > 12.3 that account for most of the observed opacity in He II Ly alpha. The He II to H I column density ratio ranges from 1 to >1000 with an average of ~80. Ratios of 100 in many locations indicate additional contributions from starburst galaxies or heavily filtered quasar radiation. The presence of He II Ly alpha absorbers with no H I counterparts indicates that structure is present even in low-density regions, consistent with theoretical predictions of structure formation through gravitational instability.

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Version 1, 2001-08-09, ArXiv
Published version: Science, 293 (5532), 1112.

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