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Astron. Astrophys. 329, 30-38 (1998)

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Evolution of the Lyman [FORMULA] forest from high to low redshift

Rüdiger Riediger 1, Patrick Petitjean 2, 3 and Jan P. Mücket 1

1 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
2 Institut d'Astrophysique de Paris - CNRS, 98bis Boulevard Arago, F-75014 Paris, France
3 UA CNRS 173- DAEC, Observatoire de Paris-Meudon, F-92195 Meudon Principal Cedex, France

Received 30 January 1997 / Accepted 12 September 1997


We study the evolution with redshift, from [FORMULA] to [FORMULA], of the Lyman [FORMULA] forest in a CDM model using numerical simulations including collisionless particles only. The baryonic component is assumed to follow the dark matter distribution.

We distinguish between two populations of particles: Population [FORMULA] traces the filamentary structures of the dark matter, evolves slowly with redshift and, for [FORMULA], dominates the number density of lines at [FORMULA] ; most of population [FORMULA] is located in underdense regions and for the same column densities, disappears rapidly at high redshift.

We generate synthetic spectra from the simulation and show that the redshift evolution of the Lyman [FORMULA] forest (decrement, [FORMULA] distribution) is well reproduced over the whole redshift range for [FORMULA] and [FORMULA] at [FORMULA] where [FORMULA] is the UV background flux intensity in units of [FORMULA] erg cm-2 s-1 Hz-1 sr-1.

The total number of lines with [FORMULA] remains approximately constant from [FORMULA] to [FORMULA]. At [FORMULA], the number density of lines per unit redshift with [FORMULA] is of the order of 400, 100, and 20 respectively. Therefore, at low redshift, if most of the strong ( [FORMULA] ) lines are expected to be associated with galaxies, the bulk of the Lyman [FORMULA] forest however should have lower equivalent width and should not be tightly correlated with galaxies.

Key words: large-scale structure – intergalactic medium – quasars: absorption lines

Send offprint requests to: R. Riediger

© European Southern Observatory (ESO) 1998

Online publication: November 24, 1997