Suite of hydrodynamical simulations for the            Lyman-α          forest with massive neutrinos

International audienceThe signature left in quasar spectra by neutral hydrogen in the Universe allows          constraining the sum of the neutrino masses with a better sensitivity than laboratory          experiments and may shed new light on the neutrino mass hierarchy and the absolute          mass-scale of neutrinos. Constraints on cosmological parameters and on the dark energy          equation of state can also be derived from a joint parameter estimation procedure.          However, this requires a detailed modeling of the line-of-sight power spectrum of the          transmitted flux in the Lyman-α (Lyα) forest on scales ranging from a few to hundreds          of megaparsecs, which in turn demands the inclusion and careful treatment of cosmological          neutrinos. To this end, we present here a suite of state-of-the-art hydrodynamical          simulations with cold dark matter (CDM), baryons and massive neutrinos, specifically          targeted for modeling the low-density regions of the intergalactic medium (IGM) as probed          by the Lyα          forest at high-redshift. The simulations span volumes ranging from (25 h-1            Mpc)3 to (100              h-1 Mpc)3, and were made using          either 3 × 1923 ≃            21 million or 3 ×              7683 ≃ 1.4 billion particles. The resolution of the          various runs was further enhanced, so that we reached the equivalent of 3 × 30723 ≃ 87 billion particles          in a (100 h-1              Mpc)3 box size. The chosen cosmological parameters are          compatible with the latest Planck 2013 results, although we also explored          the effect of slight variations in the main cosmological and astrophysical parameters. We          adopted a particle-type implementation of massive neutrinos, and consider three degenerate          species with masses ∑                mν =              0.1,0.2,0.3,0.4,          and 0.8 eV, respectively. We          improved on previous studies in several ways, in particular with updated routines for IGM          radiative cooling and heating processes, and initial conditions based on second-order          Lagrangian perturbation theory (2LPT) rather than the Zel’dovich approximation. This          allowed us to safely start our runs at relatively low redshift (z = 30), which reduced the          shot-noise contamination in the neutrino component and the CPU consumption. In addition to          providing technical details on the simulations, we present the first analysis of the          nonlinear three- and one-dimensional matter and flux power spectra from these models, and          characterize the statistics of the transmitted flux in the Lyα forest including the          effect of massive neutrinos. In synergy with recent data from the Baryon Acoustic          Spectroscopic Survey (BOSS) and the Planck satellite, and with a grid of          corresponding neutrino-less simulations, our realizations will allow us to constrain          cosmological parameters and neutrino masses directly from the Lyα forest with improved          sensitivity. In addition, our simulations can be useful for a broader variety of          cosmological and astrophysical applications, ranging from the three-dimensional modeling          of the Lyα          forest to cross-correlations between different probes, studying the expansion history of          the Universe including massive neutrinos, and particle-physics related topics. Moreover,          while our simulations have been specifically designed to meet the requirements of the BOSS          survey, they can also be used for upcoming or future experiments – such as eBOSS and          DESI