Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981a%26a....94..359o&link_type=abstract
Astronomy and Astrophysics, Vol. 94, P. 359, 1981
Astronomy and Astrophysics
Astrophysics
81
Scientific paper
Superclusters with diameters up to 50 Mpc or more are the principal remaining features reflecting the structure of the early universe. They probably contain most of the rich clusters of galaxies and possibly the majority of all galaxies. Their flat or oblong shapes suggest that they have formed via dissipational processes, in the way discussed by Zeldovich and his collaborators. Galaxies and clusters are supposed to have formed and evolved only after the initial collapse of these "pancakes". The prevalence of flat superclusters is a consequence of the expansion of the universe, which makes initial irregularities generally collapse into flat or oblong structures.
The separation between major superclusters at z= 2.5 is of the same order as that between the strongest Lyman α absorption systems observed by Sargent et al. (1980a) in six quasars between z = 2.2 and 3.3. This suggests that the absorption systems may be due to pancake gas that has remained uncondensed. The H I column densities observed are shown to be compatible with this interpretation. This model receives further support from other observations by Sargent et al. viz., the apparent absence of carbon lines in the Lyman α systems, indicating that the gas is primeval, and the apparent lack of clustering in the Lyman α lines which, if it could be substantiated, would indicate that they do not originate in galaxies.
In one of the most interesting studies of the last quarter century Sargent et al. (1980) have investigated the unidentified absorption lines shortward of the Lα emission line in six distant quasars. They give convincing evidence that practically all these lines must be ascribed to Lα absorption in bodies of gas which are not connected with the quasars themselves, but lie randomly distributed over the intervening intergalactic space, with an average line-of-sight spacing of 150 Mpc when reduced to z=0 (with H0 = 100 km s-1 Mpc-1 and Ω0 = 0.1) =0.1). The average column density per Lα absorption system is ≃1014 at cm-2.
The authors suggest that these discrete absorption lines are due to a population of gas masses with diameters of the order of 1-10 kpc, which are roughly equally abundant as galaxies, but whose characteristics are different.
In this note I suggest that the lines might originate in super- clusters instead of in the unknown objects hypothesized by Sargent et al. A principal motivation for this idea is that the average line-of-sight separation between the absorbers is approximately that between the major superclusters of galaxies in our vicinity.
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