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We present predictions for cosmic evolution of populations of supermassive black holes (SMBHs) forming from Population III.1 seeds, i.e. early, metal-free dark matter minihaloes forming far from other sources, parametrized by isolation distance, d iso. Extending previous work that explored this scenario to z  = 10, we follow evolution of a |$(60\, {\rm {Mpc}})^3$| volume to z  = 0. We focus on evolution of SMBH comoving number densities, halo occupation fractions, angular clustering, and 3D clustering, exploring a range of d iso constrained by observed local number densities of SMBHs. We also compute synthetic projected observational fields, in particular, a case comparable to the Hubble Ultra Deep Field. We compare Pop III.1 seeding to a simple halo mass threshold model, commonly adopted in cosmological simulations of galaxy formation. Major predictions of the Pop III.1 model include that all SMBHs form by z ∼ 25, after which their comoving number densities are near-constant, with low merger rates. Occupation fractions evolve to concentrate SMBHs in the most massive haloes by z  = 0, but with rare cases of SMBHs in haloes down to |$\sim 10^8\, M_\odot$|⁠. The d iso scale at epoch of formation, e.g. |$100\,$| kpc-proper at z ∼ 30, i.e. |$\sim 3\,$| Mpc-comoving, is imprinted in the SMBH two-point angular correlation function, remaining discernible as a low-amplitude feature to z ∼ 1. The SMBH 3D two-point correlation function at z  = 0 also shows lower amplitude compared to equivalently massive haloes. We discuss prospects for testing these predictions with observational surveys of SMBH populations. [ABSTRACT FROM AUTHOR]

We present the merging of the Particle-Mesh (PM) relativistic gevolution code with the TreePM gadget-4 code, with the aim of studying general relativity effects in cosmology. Our code, called grgadget , is able to track the evolution of metric perturbations in the weak field limit by using gevolution 's implementation of a relativistic PM in the Poisson gauge. To achieve this, starting from gevolution , we have written a c++ library called libgevolution , which allows a code to access and use the same abstractions and resources that gevolution uses for its PM-only N -body simulations. The code works under the assumption that particle interactions at short distances can be approximated as Newtonian, so that we can combine the forces computed with a Newtonian Tree with those computed with a relativistic PM. The result is a TreePM simulation code that represents metric perturbations at the scales where they are relevant while resolving non-linear structures. We validate our code by closely matching gadget-4 forces, computed with the Tree switched off, with those computed with libgevolution in the Newtonian limit. With grgadget , we obtain a matter power spectrum that is compatible with Newtonian gadget-4 at small scales and contains GR features at large scales that are consistent with results obtained with gevolution. We demonstrate that, due to the better resolution of the highly non-linear regime, the representation of the relativistic fields sampled on the mesh improves with respect to the PM-only simulations. [ABSTRACT FROM AUTHOR]

The generation of simulated convergence maps is of key importance in fully exploiting weak lensing by large-scale structure (LSS) from which cosmological parameters can be derived. In this paper, we present an extension of the pinocchio code that produces catalogues of dark matter haloes so that it is capable of simulating weak lensing by Modify LSS into Large Scale Structures (LSS). Like wl-moka , the method starts with a random realization of cosmological initial conditions, creates a halo catalogue and projects it on to the past light-cone, and paints in haloes assuming parametric models for the mass density distribution within them. Large-scale modes that are not accounted for by the haloes are constructed using linear theory. We discuss the systematic errors affecting the convergence power spectra when Lagrangian perturbation theory at increasing order is used to displace the haloes within pinocchio , and how they depend on the grid resolution. Our approximate method is shown to be very fast when compared to full ray-tracing simulations from an N -body run and able to recover the weak lensing signal, at different redshifts, with a few percent accuracy. It also allows for quickly constructing weak lensing covariance matrices, complementing pinocchio 's ability of generating the cluster mass function and galaxy clustering covariances and thus paving the way for calculating cross-covariances between the different probes. This work advances these approximate methods as tools for simulating and analysing survey data for cosmological purposes. [ABSTRACT FROM AUTHOR]

We present predictions of spectral energy distributions (SEDs), from the UV to the FIR, of simulated galaxies at z = 0. These were obtained by post-processing the results of an N-body+hydro simulation of a cosmological box of side 25 Mpc, which uses the Multi-Phase Particle Integrator (MUPPI) for star formation and stellar feedback, with the GRASIL-3D radiative transfer code that includes reprocessing of UV light by dust. Physical properties of our sample of ~500 galaxies resemble observed ones, though with some tension at small and large stellar masses. Comparing predicted SEDs of simulated galaxies with different samples of local galaxies, we find that these resemble observed ones, when normalized at 3.6 µm. A comparison with the Herschel Reference Survey shows that the average SEDs of galaxies, divided in bins of star formation rate (SFR), are reproduced in shape and absolute normalization to within a factor of ~2, while average SEDs of galaxies divided in bins of stellar mass show tensions that are an effect of the difference of simulated and observed galaxies in the stellar mass-SFR plane. We use our sample to investigate the correlation of IR luminosity in Spitzer and Herschel bands with several galaxy properties. SFR is the quantity that best correlates with IR light up to 160 µm, while at longer wavelengths better correlations are found with molecular mass and, at 500 μm, with dust mass. However, using the position of the FIR peak as a proxy for cold dust temperature, we assess that heating of cold dust is mostly determined by SFR, with stellar mass giving only a minor contribution. We finally show how our sample of simulated galaxies can be used as a guide to understand the physical properties and selection biases of observed samples. [ABSTRACT FROM AUTHOR]

We present the latest version of pinocchio, a code that generates catalogues of dark matter haloes in an approximate but fast way with respect to an N-body simulation. This code version implements a new on-the-fly production of halo catalogue on the past light cone with continuous time sampling, and the computation of particle and halo displacements are extended up to third-order Lagrangian perturbation theory (LPT), in contrast with previous versions that used Zel'dovich approximation. We run pinocchio on the same initial configuration of a reference N-body simulation, so that the comparison extends to the object-by-object level. We consider haloes at redshifts 0 and 1, using different LPT orders either for halo construction or to compute halo final positions. We compare the clustering properties of pinocchio haloes with those from the simulation by computing the power spectrum and two-point correlation function in real and redshift space (monopole and quadrupole), the bispectrum and the phase difference of halo distributions. We find that 2LPT and 3LPT give noticeable improvement. 3LPT provides the best agreement with N-body when it is used to displace haloes, while 2LPT gives better results for constructing haloes. At the highest orders, linear bias is typically recovered at a few per cent level. In Fourier space and using 3LPT for halo displacements, the halo power spectrum is recovered to within 10 per cent up to kmax ~0.5 h Mpc-1. The results presented in this paper have interesting implications for the generation of large ensemble of mock surveys for the scientific exploitation of data from big surveys. [ABSTRACT FROM AUTHOR]

Recent inspections of local available data suggest that the almost linear relation between the stellar mass of spheroids (Msph) and the mass of the super massive black holes (BHs), residing at their centres, shows a break below Msph ~ 1010M⊙, with a steeper, about quadratic relation at smaller masses. We investigate the physical mechanisms responsible for the change in slope of this relation, by comparing data with the results of the semi-analytic model of galaxy formation MORGANA, which already predicted such a break in its original formulation. We find that the change of slope is mostly induced by effective stellar feedback in star-forming bulges. The shape of the relation is instead quite insensitive to other physical mechanisms connected to BH accretion such as disc instabilities, galaxy mergers, active galactic nucleus (AGN) feedback, or even the exact modelling of accretion on to the BH, direct or through a reservoir of low angular momentum gas. Our results support a scenario where most stars form in the disc component of galaxies and are carried to bulges through mergers and disc instabilities, while accretion on to BHs is connected to star formation in the spheroidal component. Therefore, a model of stellar feedback that produces stronger outflows in star-forming bulges than in discs will naturally produce a break in the scaling relation. Our results point to a form of co-evolution especially at lower masses, below the putative break, mainly driven by stellar feedback rather than AGN feedback. [ABSTRACT FROM AUTHOR]

We present a quantification of the properties of bars in two N-body+ smoothed particle hydrodynamics cosmological simulations of spiral galaxies, named GA and AqC. The initial conditions were obtained using the zoom-in technique and represent two dark matter haloes of 2-3 x 1012 M⊙, available at two different resolutions. The resulting galaxies are presented in the companion paper of Murante et al. We find that the GA galaxy has a bar of length 8.8 kpc, present at the two resolution levels even though with a slightly different strength. Classical bar signatures (e.g. pattern of streaming motions, high m = 2 Fourier mode with roughly constant phase) are consistently found at both resolutions. Though a close encounter with a merging satellite at z ~ 0.6 (mass ratio 1: 50) causes a strong, transient spiral pattern and some heating of the disc, we find that bar instability is due to secular process, caused by a low Toomre parameter Q ≲ 1 due to accumulation of mass in the disc. The AqC galaxy has a slightly different history: it suffers a similar tidal disturbance due to a merging satellite at z ~ 0.5 but with a mass ratio of 1: 32, that triggers a bar in the high-resolution simulation, while at low resolution the merging is found to take place at a later time, so that both secular evolution and merging are plausible triggers for bar instability. [ABSTRACT FROM AUTHOR]

We measure and quantify properties of galactic outflows and diffuse gas at z ≥ 1 in cosmological hydrodynamical simulations. Our novel subresolution model, Multi-Phase Particle Integrator (MUPPI), implements supernova feedback using fully local gas properties, where the wind velocity and mass loading are not given as input. We find the following trends at z = 2 by analysing central galaxies having a stellar mass higher than 109M⊙. The outflow velocity and mass outflow rate (Ṁout) exhibit positive correlations with galaxy mass and with the star formation rate (SFR). However, most of the relations present a large scatter. The outflow mass loading factor (η) is between 0.2 and 10. The comparison effective model generates a constant outflow velocity, and a negative correlation of η with halo mass. The number fraction of galaxies where outflow is detected decreases at lower redshifts, but remains more than 80 per cent over z = 1-5. The outflow velocity correlation with SFR becomes flatter at z = 1, and η displays a negative correlation with halo mass in massive galaxies. Our study demonstrates that both the MUPPI and effective models produce significant outflows at ~1/10 of the virial radius; at the same time shows that the properties of outflows generated can be different from the input speed and mass loading in the effective model. Our MUPPI model, using local properties of gas in the subresolution recipe, is able to develop galactic outflows whose properties correlate with global galaxy properties, and consistent with observations. [ABSTRACT FROM AUTHOR]

We present results of cosmological simulations of disc galaxies carried out with the gadget-3 TreePM+SPH code, where star formation and stellar feedback are described using our MUlti Phase Particle Integrator model. This description is based on a simple multiphase model of the interstellar medium at unresolved scales, where mass and energy flows among the components are explicitly followed by solving a system of ordinary differential equations. Thermal energy from supernovae is injected into the local hot phase, so as to avoid that it is promptly radiated away. A kinetic feedback prescription generates the massive outflows needed to avoid the overproduction of stars. We use two sets of zoomed-in initial conditions of isolated cosmological haloes with masses (2-3) × 1012M⊙, both available at several resolution levels. In all cases we obtain spiral galaxies with small bulge-over-total stellar mass ratios (B/T ~ 0.2), extended stellar and gas discs, flat rotation curves and realistic values of stellar masses. Gas profiles are relatively flat, molecular gas is found to dominate at the centre of galaxies, with star formation rates following the observed Schmidt-Kennicutt relation. Stars kinematically belonging to the bulge form early, while disc stars show a clear inside-out formation pattern and mostly form after redshift z = 2. However, the baryon conversion efficiencies in our simulations differ from the relation given by Moster et al. at a 3σ level, thus indicating that our stellar discs are still too massive for the dark matter halo in which they reside. Results are found to be remarkably stable against resolution. This further demonstrates the feasibility of carrying out simulations producing a realistic population of galaxies within representative cosmological volumes, at a relatively modest resolution. [ABSTRACT FROM AUTHOR]

We compare predictions of cooled masses and cooling rates from three stripped-down semi-analytic models (SAMs) of galaxy formation with the results of N-body+Smoothed Particle Hydrodynamics (SPH) simulations with gas particle mass of 3.9 × 106 h−1 M⊙, where radiative cooling of a gas of primordial composition is implemented. We also run a simulation where cooling is switched on at redshift ∼2, in order to test cooling models in a regime in which their approximations are expected to be valid. We confirm that cooling models implemented in SAMs are able to predict the amount of cooled mass at z = 0 to within ∼20 per cent. However, some relevant discrepancies are found. (i) When the contribution from poorly resolved haloes is subtracted out, SAMs tend to underpredict by ∼30 per cent the mass that cools in the infall-dominated regime. (ii) At large halo masses, SAMs tend to overpredict cooling rates, though the numerical result may be affected by the use of a standard version of SPH. (iii) As found in our previous work, cooling rates are found to be significantly affected by model details: simulations disfavour models with large cores and with quenching of cooling at major mergers. (iv) When cooling is switched on at z ∼ 2, cold gas accumulates very quickly in the simulated haloes. This accumulation is reproduced by SAMs with varying degrees of accuracy. [ABSTRACT FROM AUTHOR]

We present a perturbative treatment of non-linear galaxy clustering in the context of the cubic Galileon modified gravity model, in terms of second-order Lagrangian Perturbation theory and an extension of ellipsoidal collapse that includes Vainshtein screening. We numerically implement such prescriptions in the approximate pinocchio code, and use it to generate realizations of the matter density field and halo catalogues with different prescriptions for ellipsoidal collapse. We investigate the impact of three different approximations in the computation of collapse times on the halo mass function, halo bias, and matter power spectrum. In the halo mass function, both the modified gravity effect and the screening effect are significant in the high-mass end, similar to what is found for other MG models. We perform a comparison with N -body simulations to assess the validity of our approach, and show that we can reproduce the same trend observed in simulations for all quantities considered. With a simple modification to the grouping algorithm of pinocchio to take into account the gravity modification, and without the need to re-calibrate the algorithm, we show that we can reproduce the linear halo bias and the mildly non-linear matter power spectrum of simulations with good accuracy, especially for the implementation with Vainshtein screening. We stress that, while approximate, our method is orders of magnitude faster than a full N -body simulation, making it an optimal tool for the quick generation of large sets of halo catalogues for cosmological observables. [ABSTRACT FROM AUTHOR]

We calculate cosmic distributions in space and time of the formation sites of the first, 'Pop III.1' stars, exploring a model in which these are the progenitors of all supermassive black holes (SMBHs), seen in the centres of most large galaxies. Pop III.1 stars are defined to form from primordial composition gas in dark matter minihaloes with |${\sim }10^6\, \mathrm{M}_\odot$| that are isolated from neighbouring astrophysical sources by a given isolation distance, d iso. We assume Pop III.1 sources are seeds of SMBHs, based on protostellar support by dark matter annihilation heating that allows them to accrete a large fraction of their minihalo gas, i.e. |${\sim }10^5\, \mathrm{M}_\odot$|⁠. Exploring d iso from 10 to |$100\, \rm {kpc}$| (proper distances), we predict the redshift evolution of Pop III.1 source and SMBH remnant number densities. The local, |$z$|  = 0 density of SMBHs constrains |$d_{\rm {iso}}\lesssim 100\, \rm {kpc}$| (i.e. |$3\, \rm {Mpc}$| comoving distance at |$z$| ≃ 30). In our simulated (⁠|${\sim }60\, \rm {Mpc})^3$| comoving volume, Pop III.1 stars start forming just after |$z$|  = 40. Their formation is largely complete by |$z$| ≃ 25–20 for d iso = 100– |$50\, \rm {kpc}$|⁠. We follow source evolution to |$z$|  = 10, by which point most SMBHs reside in haloes with |${\gtrsim }10^8\, \mathrm{M}_\odot$|⁠. Over this period, there is relatively limited merging of SMBHs for these values of d iso. We also predict SMBH clustering properties at |$z$|  = 10: feedback suppression of neighbouring sources leads to relatively flat angular correlation functions. [ABSTRACT FROM AUTHOR]

We compare the measurements of the bispectrum and the estimate of its covariance obtained from a set of different methods for the efficient generation of approximate dark matter halo catalogues to the same quantities obtained from full N -body simulations. To this purpose we employ a large set of 300 realizations of the same cosmology for each method, run with matching initial conditions in order to reduce the contribution of cosmic variance to the comparison. In addition, we compare how the error on cosmological parameters such as linear and non-linear bias parameters depends on the approximate method used for the determination of the bispectrum variance. As general result, most methods provide errors within 10 per cent of the errors estimated from N -body simulations. Exceptions are those methods requiring calibration of the clustering amplitude but restrict this to 2-point statistics. Finally we test how our results are affected by being limited to a few hundreds measurements from N -body simulation by comparing with a larger set of several thousands of realizations performed with one approximate method. [ABSTRACT FROM AUTHOR]

We present cosmological zoom-in hydrodynamical simulations for the formation of disc galaxies, implementing dust evolution and dust promoted cooling of hot gas. We couple an improved version of our previous treatment of dust evolution, which adopts the two-size approximation to estimate the grain-size distribution, with the MUPPI star formation and feedback subresolution model. Our dust evolution model follows carbon and silicate dust separately. To distinguish differences induced by the chaotic behaviour of simulations from those genuinely due to different simulation set-up, we run each model six times, after introducing tiny perturbations in the initial conditions. With this method, we discuss the role of various dust-related physical processes and the effect of a few possible approximations adopted in the literature. Metal depletion and dust cooling affect the evolution of the system, causing substantial variations in its stellar, gas, and dust content. We discuss possible effects on the Spectral Energy Distribution of the significant variations of the size distribution and chemical composition of grains, as predicted by our simulations during the evolution of the galaxy. We compare dust surface density, dust-to-gas ratio, and small-to-large grain mass ratio as a function of galaxy radius and gas metallicity predicted by our fiducial run with recent observational estimates for three disc galaxies of different masses. The general agreement is good, in particular taking into account that we have not adjusted our model for this purpose. [ABSTRACT FROM AUTHOR]

We present a new implementation of the GAlaxy Evolution and Assembly (gaea) semi-analytic model, that features an improved modelling of the process of cold gas accretion on to supermassive black hole (SMBHs), derived from both analytic arguments and high-resolution simulations. We consider different scenarios for the loss of angular momentum required for the available cold gas to be accreted on to the central SMBHs, and we compare different combinations of triggering mechanisms, including galaxy mergers and disc instabilities in star-forming discs. We compare our predictions with the luminosity function (LF) observed for active galactic nuclei (AGNs) and we confirm that a non-instantaneous accretion time-scale (either in the form of a low-angular momentum reservoir or as an assumed light-curve evolution) is needed in order to reproduce the measured evolution of the AGN-LF and the so-called AGN-downsizing trend. Moreover, we also study the impact of AGN feedback, in the form of AGN-driven outflows, on the SF properties of model galaxies, using prescriptions derived both from empirical studies and from numerical experiments. We show that AGN-driven outflows are effective in suppressing the residual star formation rate in massive galaxies (>1011 M⊙) without changing their overall assembly history. These winds also affect the SFR of lower mass galaxies, resulting in a too large fraction of passive galaxies at <1010 M⊙. Finally, we study the Eddington ratio distribution as a function of SMBH mass, showing that only objects more massive than 108 M⊙ are already in a self-regulated state as inferred from observations. [ABSTRACT FROM AUTHOR]

We investigate the accuracy of weak lensing simulations by comparing the results of five independently developed lensing simulation codes run on the same input N -body simulation. Our comparison focuses on the lensing convergence maps produced by the codes, and in particular on the corresponding PDFs, power spectra, and peak counts. We find that the convergence power spectra of the lensing codes agree to |$\lesssim 2{{\ \rm per\ cent}}$| out to scales ℓ ≈ 4000. For lensing peak counts, the agreement is better than |$5{{\ \rm per\ cent}}$| for peaks with signal-to-noise ≲ 6. We also discuss the systematic errors due to the Born approximation, line-of-sight discretization, particle noise, and smoothing. The lensing codes tested deal in markedly different ways with these effects, but they none-the-less display a satisfactory level of agreement. Our results thus suggest that systematic errors due to the operation of existing lensing codes should be small. Moreover their impact on the convergence power spectra for a lensing simulation can be predicted given its numerical details, which may then serve as a validation test. [ABSTRACT FROM AUTHOR]

We present simulations of galaxy formation, based on the gadget -3 code, in which a sub-resolution model for star formation and stellar feedback is interfaced with a new model for active galactic nucleus (AGN) feedback. Our sub-resolution model describes a multiphase interstellar medium (ISM), accounting for hot and cold gas within the same resolution element: we exploit this feature to investigate the impact of coupling AGN feedback energy to the different phases of the ISM over cosmic time. Our fiducial model considers that AGN feedback energy coupling is driven by the covering factors of the hot and cold phases. We perform a suite of cosmological hydrodynamical simulations of disc galaxies (⁠|$M_{\rm halo,DM} \simeq 2 \times 10^{12}$|  M⊙, at z  = 0), to investigate: (i) the effect of different ways of coupling AGN feedback energy to the multiphase ISM; (ii) the impact of different prescriptions for gas accretion (i.e. only cold gas, both cold and hot gas, with the additional possibility of limiting gas accretion from cold gas with high angular momentum); (iii) how different models of gas accretion and coupling of AGN feedback energy affect the coevolution of supermassive black holes (BHs) and their host galaxy. We find that at least a share of the AGN feedback energy has to couple with the diffuse gas, in order to avoid an excessive growth of the BH mass. When the BH only accretes cold gas, it experiences a growth that is faster than in the case in which both cold and hot gas are accreted. If the accretion of cold gas with high angular momentum is reduced, the BH mass growth is delayed, the BH mass at z  = 0 is reduced by up to an order of magnitude, and the BH is prevented from accreting below z ≲ 2, when the galaxy disc forms. [ABSTRACT FROM AUTHOR]

We study the accuracy of several approximate methods for gravitational dynamics in terms of halo power spectrum multipoles and their estimated covariance matrix. We propagate the differences in covariances into parameter constraints related to growth rate of structure, Alcock–Paczynski distortions, and biasing. We consider seven methods in three broad categories: algorithms that solve for halo density evolution deterministically using Lagrangian trajectories (ICE–COLA, pinocchio, and peakpatch), methods that rely on halo assignment schemes on to dark matter overdensities calibrated with a target N-body run (halogen, patchy), and two standard assumptions about the full density probability distribution function (Gaussian and lognormal). We benchmark their performance against a set of three hundred N-body simulations, running similar sets of approximate simulations with matched initial conditions, for each method. We find that most methods reproduce the monopole to within |$5{{\ \rm per\ cent}}$|⁠, while residuals for the quadrupole are sometimes larger and scale dependent. The variance of the multipoles is typically reproduced within |$10{{\ \rm per\ cent}}$|⁠. Overall, we find that covariances built from approximate simulations yield errors on model parameters within |$10{{\ \rm per\ cent}}$| of those from the N-body-based covariance. [ABSTRACT FROM AUTHOR]

We perform a suite of cosmological hydrodynamical simulations of disc galaxies, with zoomed-in initial conditions leading to the formation of a halo of mass |$M_{\rm halo, \, DM} \simeq 2 \times 10^{12}$|  M⊙ at redshift z  = 0. These simulations aim at investigating the chemical evolution and the distribution of metals in a disc galaxy, and at quantifying the effect of (i) the assumed IMF, (ii) the adopted stellar yields, and (iii) the impact of binary systems originating SNe Ia on the process of chemical enrichment. We consider either a Kroupa, Tout & Gilmore (1993) or a more top-heavy Kroupa (2001) IMF, two sets of stellar yields and different values for the fraction of binary systems suitable to give rise to SNe Ia. We investigate stellar ages, SN rates, stellar and gas metallicity gradients, and stellar α-enhancement in simulations, and compare predictions with observations. We find that a Kroupa et al. (1993) IMF has to be preferred when modelling late-type galaxies in the local Universe. On the other hand, the comparison of stellar metallicity profiles and α-enhancement trends with observations of Milky Way stars shows a better agreement when a Kroupa (2001) IMF is assumed. Comparing the predicted SN rates and stellar α-enhancement with observations supports a value for the fraction of binary systems producing SNe Ia of 0.03, at least for late-type galaxies and for the considered IMFs. Adopted stellar yields are crucial in regulating cooling and star formation, and in determining patterns of chemical enrichment for stars, especially for those located in the galaxy bulge. [ABSTRACT FROM AUTHOR]

This paper is the first in a set that analyses the covariance matrices of clustering statistics obtained from several approximate methods for gravitational structure formation. We focus here on the covariance matrices of anisotropic two-point correlation function measurements. Our comparison includes seven approximate methods, which can be divided into three categories: predictive methods that follow the evolution of the linear density field deterministically (ice-cola, peak patch, and pinocchio), methods that require a calibration with N -body simulations (patchy and halogen), and simpler recipes based on assumptions regarding the shape of the probability distribution function (PDF) of density fluctuations (lognormal and Gaussian density fields). We analyse the impact of using covariance estimates obtained from these approximate methods on cosmological analyses of galaxy clustering measurements, using as a reference the covariances inferred from a set of full N -body simulations. We find that all approximate methods can accurately recover the mean parameter values inferred using the N -body covariances. The obtained parameter uncertainties typically agree with the corresponding N -body results within 5 per cent for our lower mass threshold and 10 per cent for our higher mass threshold. Furthermore, we find that the constraints for some methods can differ by up to 20 per cent depending on whether the halo samples used to define the covariance matrices are defined by matching the mass, number density, or clustering amplitude of the parent N -body samples. The results of our configuration-space analysis indicate that most approximate methods provide similar results, with no single method clearly outperforming the others. [ABSTRACT FROM AUTHOR]

We investigate the impact of galactic outflowmodelling on the formation and evolution of a disc galaxy, by performing a suite of cosmological simulations with zoomed-in initial conditions (ICs) of a Milky Way-sized halo. We verify how sensitive the general properties of the simulated galaxy are to the way in which stellar feedback triggered outflows are implemented, keeping ICs, simulation code and star formation (SF) model all fixed. We present simulations that are based on a version of the GADGET3 code where our sub-resolution model is coupled with an advanced implementation of smoothed particle hydrodynamics that ensures a more accurate fluid sampling and an improved description of gas mixing and hydrodynamical instabilities. We quantify the strong interplay between the adopted hydrodynamic scheme and the sub-resolution model describing SF and feedback. We consider four different galactic outflow models, including the one introduced by Dalla Vecchia & Schaye (2012) and a scheme that is inspired by the Springel & Hernquist (2003) model. We find that the sub-resolution prescriptions adopted to generate galactic outflows are the main shaping factor of the stellar disc component at low redshift. The key requirement that a feedback model must have to be successful in producing a disc-dominated galaxy is the ability to regulate the high-redshift SF (responsible for the formation of the bulge component), the cosmological infall of gas from the large-scale environment, and gas fall-back within the galactic radius at low redshift, in order to avoid a too high SF rate at z = 0. [ABSTRACT FROM AUTHOR]

We use a sample of 1669 quasars (r < 20.15, 3.6 < z < 4.0) from the Baryon Oscillation Spectroscopic Survey to study the intrinsic shape of their continuum and the Lyman continuum photon escape fraction (fesc,q), estimated as the ratio between the observed flux and the expected intrinsic flux (corrected for the intergalactic medium absorption) in the wavelength range 865-885 Å rest frame. Modelling the intrinsic quasar (QSO) continuum shape with a power law, Fλ ∝ λ-γ, we find a median γ = 1.30 (with a dispersion of 0.38, no dependence on the redshift and a mild intrinsic luminosity dependence) and a mean fesc,q = 0.75 (independent of the QSO luminosity and/or redshift). The fesc,q distribution shows a peak around zero and a long tail of higher values, with a resulting dispersion of 0.7. If we assume for the QSO continuum a double power-law shape (also compatible with the data) with a break located at λbr = 1000 Å and a softening Δγ = 0.72 at wavelengths shorter than λbr, the mean fesc,q rises to 0.82. Combining our γ and fesc,q estimates with the observed evolution of the active galactic nucleus (AGN) luminosity function (LF), we compute the AGN contribution to the UV ionizing background (UVB) as a function of redshift. AGN brighter than one-tenth of the characteristic luminosity of the LF are able to produce most of it up to z ~ 3, if the present sample is representative of their properties. At higher redshifts, a contribution of the galaxy population is required. Assuming an escape fraction of Lyman continuum photons from galaxies between 5.5 and 7.6 per cent, independent of the galaxy luminosity and/or redshift, a remarkably good fit to the observational UVB data up to z ~ 6 is obtained. At lower redshift, the extrapolation of our empirical estimate agrees well with recent UVB observations, dispelling the so-called Photon Underproduction Crisis. [ABSTRACT FROM AUTHOR]

We implement novel numerical models of AGN feedback in the SPH code GADGET-3, where the energy from a supermassive black hole (BH) is coupled to the surrounding gas in the kinetic form. Gas particles lying inside a bi-conical volume around the BH are imparted a one-time velocity (10000 km s-1) increment. We perform hydrodynamical simulations of isolated cluster (total mass 1014 h-1 M⊙), which is initially evolved to form a dense cool core, having central T ≤ 106 K. A BH resides at the cluster centre, and ejects energy. The feedback-driven fast wind undergoes shock with the slower moving gas, which causes the imparted kinetic energy to be thermalized. Bipolar bubble-like outflows form propagating radially outward to a distance of a few 100 kpc. The radial profiles of median gas properties are influenced by BH feedback in the inner regions (r < 20-50 kpc). BH kinetic feedback, with a large value of the feedback efficiency, depletes the inner cool gas and reduces the hot gas content, such that the initial cool core of the cluster is heated up within a time 1.9 Gyr, whereby the core median temperature rises to above 107 K, and the central entropy flattens. Our implementation of BH thermal feedback (using the same efficiency as kinetic), within the star formation model, cannot do this heating, where the cool core remains. The inclusion of cold gas accretion in the simulations produces naturally a duty cycle of the AGN with a periodicity of 100 ofMyr. [ABSTRACT FROM AUTHOR]

We present a comparison of major methodologies of fast generating mock halo or galaxy catalogues. The comparison is done for two-point (power spectrum and two-point correlation function in real and redshift space), and the three-point clustering statistics (bispectrum and three-point correlation function). The reference catalogues are drawn from the BigMultiDark N-body simulation. Both friend-of-friends (including distinct haloes only) and spherical over-density (including distinct haloes and subhalos) catalogues have been used with the typical number density of a large volume galaxy surveys. We demonstrate that a proper biasing model is essential for reproducing the power spectrum at quasi-linear and even smaller scales. With respect to various clustering statistics, a methodology based on perturbation theory and a realistic biasing model leads to very good agreement with N-body simulations. However, for the quadrupole of the correlation function or the power spectrum, only the method based on semi-N-body simulation could reach high accuracy (1 per cent level) at small scales, i.e. r < 25 h-1 Mpc or k > 0.15 h Mpc-1. Full N-body solutions will remain indispensable to produce reference catalogues. Nevertheless, we have demonstrated that the more efficient approximate solvers can reach a few per cent accuracy in terms of clustering statistics at the scales interesting for the large-scale structure analysis. This makes them useful for massive production aimed at covariance studies, to scan large parameter spaces, and to estimate uncertainties in data analysis techniques, such as baryon acoustic oscillation reconstruction, redshift distortion measurements, etc. [ABSTRACT FROM AUTHOR]

We present a comparison of major methodologies of fast generating mock halo or galaxy catalogues. The comparison is done for two-point (power spectrum and two-point correlation function in real and redshift space), and the three-point clustering statistics (bispectrum and three-point correlation function). The reference catalogues are drawn from the BigMultiDark N-body simulation. Both friend-of-friends (including distinct haloes only) and spherical overdensity (including distinct haloes and subhalos) catalogues have been used with the typical number density of a large volume galaxy surveys. We demonstrate that a proper biasing model is essential for reproducing the power spectrum at quasi-linear and even smaller scales. With respect to various clustering statistics, a methodology based on perturbation theory and a realistic biasing model leads to very good agreement with N-body simulations. However, for the quadrupole of the correlation function or the power spectrum, only the method based on semi-N-body simulation could reach high accuracy (1 per cent level) at small scales, i.e. r < 25 h-1 Mpc or k > 0.15 h Mpc-1. Full N-body solutions will remain indispensable to produce reference catalogues. Nevertheless, we have demonstrated that the more efficient approximate solvers can reach a few per cent accuracy in terms of clustering statistics at the scales interesting for the large-scale structure analysis. This makes them useful for massive production aimed at covariance studies, to scan large parameter spaces, and to estimate uncertainties in data analysis techniques, such as baryon acoustic oscillation reconstruction, redshift distortion measurements, etc. [ABSTRACT FROM AUTHOR]