Evolution of the Lyman-alpha forest from high to low redshift

TL;DR

This study uses numerical simulations to analyze the evolution of the Lyman-alpha forest from high to low redshift, revealing how different gas populations contribute to absorption features over cosmic time.

Contribution

It introduces a model distinguishing two gas populations and demonstrates that simulations can accurately reproduce the observed evolution of the Lyman-alpha forest.

Findings

Number of lines with N(HI)>10^12 cm^-2 remains constant from z=4 to z=1.

At z=0, line densities are approximately 400, 100, and 20 for different column densities.

Most low-redshift lines are weak and not strongly correlated with galaxies.

Abstract

We study the evolution with redshift, from z=5 to z=0, of the Lyman-alpha 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)>10^14 cm^-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 Lyman-alpha forest (decrement, N(HI) distribution) is well reproduced over the whole redshift range for Omega_b*h^2=0.0125 and J_-21=0.1 at z=3 where J_-21 is the UV background flux intensity in units of 10^-21 erg cm^-2 s^-1 Hz^-1 sr^-1. The total number of lines with N(HI)>10^12 cm^-2 remains approximately constant from z=4 to z=1. At z=0, the number density of lines per unit redshift with log N(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>0.3 \AA) lines are expected to be associated with galaxies, the bulk of the Lyman-alpha forest however should have lower equivalent width and should not be tightly correlated with galaxies.