The Sherwood simulation suite: overview and data comparisons with the Lyman α forest at redshifts 2 ≤ $\textit{z}$ ≤ 5

Abstract

We introduce a new set of large-scale, high-resolution hydrodynamical simulations of the intergalactic medium: the Sherwood simulation suite. These are performed in volumes of 10$^{3}$–160$^{3}$$\textit{h}$$^{-3}$ comoving Mpc$^{3}$, span almost four orders of magnitude in mass resolution with up to 17.2 billion particles, and employ a variety of physics variations including warm dark matter and galactic outflows. We undertake a detailed comparison of the simulations to high-resolution, high signal-to-noise observations of the Ly α forest over the redshift range 2 ≤ $\textit{z}$ ≤ 5. The simulations are in very good agreement with the observational data, lending further support to the paradigm that the Ly α forest is a natural consequence of the web-like distribution of matter arising in Λcold dark matter cosmological models. Only a small number of minor discrepancies remain with respect to the observational data. Saturated Ly α absorption lines with column densities $\textit{N}$$_{HI}$>10$^{14.5}$cm$^{-2}$ at 2 < $\textit{z}$ < 2.5 are underpredicted in the models. An uncertain correction for continuum placement bias is required to match the distribution and power spectrum of the transmitted flux, particularly at $\textit{z}$ > 4. Finally, the temperature of intergalactic gas in the simulations may be slightly too low at $\textit{z}$ = 2.7 and a flatter temperature–density relation is required at $\textit{z}$ = 2.4, consistent with the expected effects of non-equilibrium ionization during He $\tiny \text{II}$ reionization.