Accurate cosmology from upcoming weak lensing surveys relies on knowledge of the total matter power spectrum at percent level at scales k < 10 h/Mpc, for which modelling the impact of baryonic physics is crucial. We compare measurements of the total matter power spectrum from the Horizon cosmological hydrodynamical simulations: a dark matter-only run, one with full baryonic physics, and another lacking Active Galactic Nuclei (AGN) feedback. Baryons cause a suppression of power at k ≃ 10 h/Mpc of < 15% at z = 0, and an enhancement of a factor of a few at smaller scales due to the more efficient cooling and star formation. The results are sensitive to the presence of the highest mass haloes in the simulation and the distribution of dark matter is also impacted up to a few percent. The redshift evolution of the effect is non-monotonic throughout z = 0 − 5 due to an interplay between AGN feedback and gas pressure, and the growth of structure. We investigate the effectiveness of an analytic "baryonic correction model" in describing our results. We require a different redshift evolution and propose an alternative fitting function with 4 free parameters that reproduces our results within 5%. Compared to other simulations, we find the impact of baryonic processes on the total matter power spectrum to be smaller at z = 0. Correspondingly, our results suggest that AGN feedback is not strong enough in the simulation. Total matter power spectra from the Horizon simulations are made publicly available at https://www.horizon-simulation.org/catalogues.html.

We present the first spectroscopic measurements of the [O iii] 5007Å line in two z ∼ 3.1 Lymanalpha emitting galaxies (LAEs) using the new near-infrared instrument LUCIFER1 on the 8.4m Large Binocular Telescope (LBT). We also describe the optical imaging and spectroscopic observations used to identify these Ly-α emitting galaxies. Using the [O iii] line we have measured accurate systemic redshifts for these two galaxies, and discovered a velocity offset between the [O iii] and Ly-α lines in both, with the Ly-α line peaking 342 and 125 km s −1 redward of the systemic velocity. These velocity offsets imply that there are powerful outflows in high-redshift LAEs. They also ease the transmission of Ly-α photons through the interstellar medium and intergalactic medium around the galaxies. By measuring these offsets directly, we can refine both Ly-α-based tests for reionization, and Ly-α luminosity function measurements where the Ly-α forest affects the blue wing of the line. Our work also provides the first direct constraints on the strength of the [O iii] line in high-redshift LAEs. We find [O iii] fluxes of 7 and 36 ×10 −17 erg s −1 cm −2 in two z ∼ 3.1 LAEs. These lines are strong enough to dominate broad-band flux measurements that include the line (in this case, K s band photometry). Spectral energy distribution fits that do not account for the lines would therefore overestimate the 4000Å (and/or Balmer) break strength in such galaxies, and hence also the ages and stellar masses of such high-z galaxies. Subject headings: galaxies: high redshift -intergalactic medium 1 The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system;

The observed massive end of the galaxy stellar mass function is steeper than its predicted dark matter halo counterpart in the standard ΛCDM paradigm. In this paper, we investigate the impact of active galactic nuclei (AGN) feedback on star formation in massive galaxies. We isolate the impact of AGNs by comparing two simulations from the HORIZON suite, which are identical except that one also includes super massive black holes (SMBH), and related feedback models. This allows us to cross-identify individual galaxies between simulations and quantify the effect of AGN feedback on their properties, including stellar mass and gas outflows. We find that massive galaxies (M * ≥ 10 11 M ) are quenched by AGN feedback to the extent that their stellar masses decrease by up to 80% at z = 0. SMBHs affect their host halo through a combination of outflows that reduce their baryonic mass, particularly for galaxies in the mass range 10 9 M ≤ M * ≤ 10 11 M , and a disruption of central gas inflows, which limits in-situ star formation. As a result, net gas inflows onto massive galaxies, M * ≥ 10 11 M , drop by up to 70%. We measure a redshift evolution in the stellar mass ratio of twin galaxies with and without AGN feedback, with galaxies of a given stellar mass showing stronger signs of quenching earlier on. This evolution is driven by a progressive flattening of the M SMBH − M * relation with redshift, particularly for galaxies with M * ≤ 10 10 M . M SMBH /M * ratios decrease over time, as falling average gas densities in galaxies curb SMBH growth.

The first objects to arise in a cold dark matter universe present a daunting challenge for models of structure formation. In the ultra small-scale limit, CDM structures form nearly simultaneously across a wide range of scales. Hierarchical clustering no longer provides a guiding principle for theoretical analyses and the computation time required to carry out credible simulations becomes prohibitively high. To gain insight into this problem, we perform high-resolution (N=720^3 - 1584^3) simulations of an Einstein-de Sitter cosmology where the initial power spectrum is P(k) propto k^n, with -2.5 < n < -1. Self-similar scaling is established for n=-1 and n=-2 more convincingly than in previous, lower-resolution simulations and for the first time, self-similar scaling is established for an n=-2.25 simulation. However, finite box-size effects induce departures from self-similar scaling in our n=-2.5 simulation. We compare our results with the predictions for the power spectrum from (one-loop) perturbation theory and demonstrate that the renormalization group approach suggested by McDonald improves perturbation theory's ability to predict the power spectrum in the quasilinear regime. In the nonlinear regime, our power spectra differ significantly from the widely used fitting formulae of Peacock & Dodds and Smith et al. and a new fitting formula is presented. Implications of our results for the stable clustering hypothesis vs. halo model debate are discussed. Our power spectra are inconsistent with predictions of the stable clustering hypothesis in the high-k limit and lend credence to the halo model. Nevertheless, the fitting formula advocated in this paper is purely empirical and not derived from a specific formulation of the halo model.Comment: 30 pages including 10 figures; accepted for publication in MNRA