A Unified Fitting of H i and He ii Lyα Transmitted Flux of QSO HE 2347−4342 with ΛCDM Hydrodynamic Simulations

Abstract

Using cosmological hydrodynamic simulations of the boolean AND CDM model, we present a comparison between the simulation sample and real data sample of H (I) and He (II) Ly alpha transmitted flux in the absorption spectra of the QSO HE 2347-4342. The boolean AND CDM model is successful in simultaneously explaining the statistical features of both H (I) and He (II) Ly alpha transmitted flux. It includes the following features: (1) The power spectra of the transmitted flux of H (I) and He (II) can be well fitted on all scales >= 0.28 h(-1) Mpc for H and >= 1.1 h(-1) Mpc for He. (2) The Doppler parameters of absorption features of He (II) and H (I) are found to be turbulent broadening. (3) The ratio of He (II) to H (I) optical depths are substantially scattered, due to the significant effect of noise. A large part of the eta scatter is due to the noise in the He (II) flux. However, the real data contain more low-eta events than the simulation sample. This discrepancy may indicate that the mechanism leading extra fluctuations on the simulation data, such as a fluctuating UV radiation background, is needed. Yet models of these extra fluctuations should satisfy the following constraints: (1) If the fluctuations are Gaussian, they should be limited by the power spectra of observed H (I) and He (II) flux. (2) If the fluctuations are non-Gaussian, they should be limited by the observed non-Gaussian features of the H (I) and He (II) flux.