Open AccessThe Gunn–Peterson effect and the Lyman alpha forest
Author(s) -
Levshakov Sergei A.,
Kegel Wilhelm H.
Publication year - 1998
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1998.01722.x
Subject(s) - physics , intergalactic travel , lyman alpha forest , astrophysics , qsos , intergalactic medium , opacity , spectral line , population , astronomy , quasar , galaxy , redshift , quantum mechanics , demography , sociology
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 10 11 ≲ N H i 5 × 10 13 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 τ GP ∼ 0.3 at z ∼ 3 and a current baryon density Ω IGM ≃ 0.08, assuming a Hubble constant H 0 = 70 km s −1 Mpc −1 .