Semi analytic approach to understanding the distribution of neutral hydrogen in the Universe: comparison of simulations with observations

Abstract

Following Bi & Davidsen, we perform one-dimensional semianalytic simulations along the lines of sight to model the intergalactic medium (IGM). Since this procedure is computationally efficient in probing the parameter space-and reasonably accurate-we use it to recover the values of various parameters related to the IGM (for a fixed background cosmology) by comparing the model predictions with different observations. For the currently favored low-density cold dark matter model (Ω_m = 0.4, Ω_Λ = 0.6, and h = 0.65), we obtain, using statistics obtained from the transmitted flux, constraints on (1) the combination f = (Ω_Bh²)²/J_-12, where Ω_B is the baryonic density parameter and J_-12 is the total photoionization rate in units of 10^-12 s^-1, (2) temperature T₀ corresponding to the mean density, and (3) the slope ∨ of the effective equation of state of the IGM at a mean redshift z ⋍ 2.5. We find that 0.8 < T₀/ < (10⁴ Κ) < 2.5 and 1.3 < ∨ < 2.3, while the constraint obtained on ƒ is 0.020² < f < 0.032². A reliable lower bound on J_-12 can be used to put a lower bound on Ω_Bh², which can be compared with similar constraints obtained from big bang nucleosynthesis (BBN) and cosmic microwave background radiation studies. We find that if J_-12 > 1.2, the lower bound on Ω_Bh² is in violation of the BBN value.