1996A&A...308...17M

We study the evolution with redshift of the number density of Lyα clouds in a CDM model using numerical simulations including photo-ionization and cooling of the baryonic component. The photo-ionizing flux is consistently taken as proportional to the rate at which material cools below 5000K in the simulation. The number density of lines with N(HI)>10¹⁴cm^–2 given by the simulation can be approximated as dn/dz∼16.8(1+z)^0.8+0.687(1+z)^2.5 which fits well the data at any redshift. The number of weaker lines is reproduced within a factor of two and does not decrease with time as fast as the number of strong lines. For N(HI)>10¹³cm^–2, we find dn/dz∝(1+z)^0.7. At z=0, the two-point correlation function for Lymanα clouds with N(HI)>10¹³ and >10¹⁴cm^–2 has a slope ~-1.75 comparable to the slope of the two point correlation function for the galaxy distribution. The signal is higher for stronger lines for separations smaller than 1 Mpc. Part of the Lymanα forest is indeed associated with galaxies however the overall picture is that Lyα absorption lines originate in the warm gas that traces the potential wells of filamentary structures defined by the dark matter.