1998A&A...329...30R

We study the evolution with redshift, from z∼5 to z=0, of the Lymanα 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 P_s traces the filamentary structures of the dark matter, evolves slowly with redshift and, for N(HI)>10¹⁴cm^–2, dominates the number density of lines at z<3; most of population P_u 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 Lymanα forest (decrement, N(HI) distribution) is well reproduced over the whole redshift range for {OMEGA}_bh²∼0.0125 and J_–21≃0.1 at z∼3 where J_–21 is the UV background flux intensity in units of 10^–21erg/cm²/s/Hz/sr. The total number of lines with N(HI)>10¹²cm^–2 remains approximately constant from z∼4 to z=1. At z∼0, the number density of lines per unit redshift with logN(HI)>12, 13, 14 is of the order of 400, 100, and 20 respectively. Therefore, at low redshift, if most of the strong (w_r>0.3Å) lines are expected to be associated with galaxies, the bulk of the Lymanα forest however should have lower equivalent width and should not be tightly correlated with galaxies.