Journal Article

The Gunn—Peterson effect and the Lyman alpha forest

Sergei A. Levshakov and Wilhelm H. Kegel

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 301, issue 2, pages 323-327
Published in print December 1998 | ISSN: 0035-8711
Published online December 1998 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1046/j.1365-8711.1998.01722.x
The Gunn—Peterson effect and the Lyman alpha forest

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Abstract

We show that spatial correlations in a stochastic large-scale velocity field in an otherwise smooth intergalactic medium (homogeneous comoving density) superposed on the general Hubble flow may cause a ‘line-like’ structure in QSO spectra similar to the population of unsaturated Lyα forest lines which usually are attributed to individual clouds with 1011NHi 5 × 1013 cm−2. Therefore there is no clear observational distinction between a diffuse intergalactic medium and discrete intergalactic clouds. It follows that the H i density in the diffuse intergalactic medium might be substantially underestimated if it is determined from the observed intensity distribution near the apparent continuum in high-resolution spectra of QSOs. Our tentative estimate implies a diffuse neutral hydrogen opacity τGP ∼ 0.3 at z ∼ 3 and a current baryon density ΩIGM ≃ 0.08, assuming a Hubble constant H0 = 70 km s−1 Mpc−1.

Keywords: line: formation; line: profiles; quasars: absorption lines

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

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