We present the Model for the Rise of Galaxies and Active Nuclei (MORGANA), a new code for the formation and evolution of galaxies and active galactic nuclei (AGNs). Starting from the merger trees of dark matter (DM) haloes and a model for the evolution of substructure within the haloes, the complex physics of baryons is modelled with a set of state-of-the-art models that describe the mass, metal and energy flows between the various components (baryonic halo, bulge, disc) and phases (cold and hot gas, stars) of a galaxy. These flows are then numerically integrated to produce predictions for the evolution of galaxies. The processes of shock-heating and cooling, star formation, feedback, galactic winds and superwinds, accretion on to black holes and AGN feedback are described by new models. In particular, the evolution of the halo gas explicitly follows the thermal and kinetic energies of the hot and cold phases, while star formation and feedback follow the results of the multiphase model recently proposed by Monaco. The increased level of sophistication of these models allows to move from a phenomenological description of gas physics, based on simple scalings with the depth of the DM halo potential, towards a fully physically motivated one. We deem that this is fully justified by the level of maturity and rough convergence reached by the latest versions of numerical and semi-analytic models of galaxy formation. The comparison of the predictions of MORGANA with a basic set of galactic data reveals from the one hand an overall rough agreement, and from the other hand highlights a number of well-or less-known problems: (i) producing the cut-off of the luminosity function requires to force the quenching of the late cooling flows by AGN feedback, (ii) the normalization of the Tully-Fisher relation of local spirals cannot be recovered unless the DM haloes are assumed to have a very low concentration, (iii) the mass function of H I gas is not easily fitted at small masses, unless a similarly low concentration is assumed, (iv) there is an excess of small elliptical galaxies at z = 0. These discrepancies, more than the points of agreement with data, give important clues on the missing ingredients of galaxy formation.
We study the evolution of dark matter satellites orbiting inside more massive haloes using semi-analytical tools coupled with high-resolution N-body simulations. We select initial satellite sizes, masses, orbital energies, and eccentricities as predicted by hierarchical models of structure formation. Both the satellite (of initial mass M s,0 ) and the main halo (of mass M h ) are described by a Navarro, Frenk & White density profile with various concentrations.We explore the interplay between dynamic friction and tidal mass loss/evaporation in determining the final fate of the satellite. We provide a user-friendly expression for the dynamic friction time-scale τ df,live and for the disruption time for a live (i.e. mass-losing) satellite. This can be easily implemented into existing semi-analytical models of galaxy formation improving considerably the way they describe the evolution of satellites.Massive satellites (M s,0 > 0.1M h ) starting from typical cosmological orbits sink rapidly (irrespective of the initial circularity) toward the centre of the main halo where they merge after a time τ df,rig , as if they were rigid. Satellites of intermediate mass (0.01M h < M s,0 < 0.1M h ) suffer severe tidal mass losses as dynamic friction reduces their pericentre distance. In this case, mass loss increases substantially their decay time with respect to a rigid satellite. The final fate depends on the concentration of the satellite, c s , relative to that of the main halo, c h . Only in the unlikely case where c s /c h 1 are satellites disrupted. In this mass range, τ df,live gives a measure of the merging time. Among the satellites whose orbits decay significantly, those that survive must have been moving preferentially on more circular orbits since the beginning as dynamical friction does not induce circularization. Lighter satellites (M s,0 < 0.01M h ) do not suffer significant orbital decay and tidal mass loss stabilizes the orbit even further. Their orbits should map those at the time of entrance into the main halo.After more than a Hubble time satellites have masses M s ∼ 1-10 per cent M s,0 , typically, implying M s < 0.001M h for the remnants. In a Milky-Way-like halo, light satellites should be present even after several orbital times with their baryonic components experimenting morphological changes due to tidal stirring.They coexist with the remnants of more massive satellites depleted in their dark matter content by the tidal field, which should move preferentially on tightly bound orbits.
pinocchio (PINpointing Orbit‐Crossing Collapsed HIerarchical Objects) is a new algorithm proposed recently by Monaco et al. (Paper I) for identifying dark matter haloes in a given numerical realization of the linear density field in a hierarchical universe. Mass elements are assumed to have collapsed after undergoing orbit crossing, as computed using perturbation theory. It is shown that Lagrangian perturbation theory, and in particular its ellipsoidal truncation, is able to predict accurately the collapse, in the orbit‐crossing sense, of generic mass elements. Collapsed points are grouped into haloes using an algorithm that mimics the hierarchical growth of structure through accretion and mergers. Some points that have undergone orbit crossing are assigned to the network of filaments and sheets that connects the haloes; it is demonstrated that this network resembles closely that found in N‐body simulations. The code generates a catalogue of dark matter haloes with known mass, position, velocity, merging history and angular momentum. It is shown that the predictions of the code are very accurate when compared with the results of large N‐body simulations that cover a range of cosmological models, box sizes and numerical resolutions. The mass function is recovered with an accuracy of better than 10 per cent in number density for haloes with at least 30–50 particles. A similar accuracy is reached in the estimate of the correlation length r0. The good agreement is still valid on the object‐by‐object level, with 70–100 per cent of the objects with more than 50 particles in the simulations also identified by our algorithm. For these objects the masses are recovered with an error of 20–40 per cent, and positions and velocities with a root mean square error of ∼1–2 Mpc (0.5–2 grid lengths) and ∼100 km s−1, respectively. The recovery of the angular momentum of haloes is considerably noisier, and accuracy at the statistical level is achieved only by introducing free parameters. The algorithm requires negligible computer time as compared with performing a numerical N‐body simulation.
We present a new algorithm (PINOCCHIO, PINpointing Orbit-Crossing Collapsed HIerarchical objects) to predict accurately the formation and evolution of individual dark matter haloes in a given realization of an initial linear density field. Compared with the halo population formed in a large (360 3 particles) collisionless simulation of a CDM universe, our method is able to predict to better than 10 per cent statistical quantities such as the mass function, two-point correlation function and progenitor mass function of the haloes. Masses of individual haloes are estimated accurately as well, with errors typically of order 30 per cent in the mass range well resolved by the numerical simulation. These results show that the hierarchical formation of dark matter haloes can be accurately predicted using local approximations to the dynamics when the correlations in the initial density field are properly taken into account. The approach allows one to automatically generate a large ensemble of accurate merging histories of haloes with complete knowledge of their spatial distribution. The construction of the full merger tree for a 256 3 realisation requires a few hours of CPU-time on a personal computer, orders of magnitude faster than the corresponding N -body simulation would take, and without needing any extensive post-processing. The technique can be efficiently used, for instance, for generating the input for galaxy formation modeling.
We study the ability of PINOCCHIO (PINpointing Orbit-Crossing Collapsed HIerarchical Objects) to predict the merging histories of dark matter (DM) haloes, comparing the PINOCCHIO predictions with the results of two large N-body simulations run from the same set of initial conditions. We focus our attention on quantities most relevant to galaxy formation and large-scale structure studies. PINOCCHIO is able to predict the statistics of merger trees with a typical accuracy of 20 per cent. Its validity extends to higher-order moments of the distribution of progenitors. The agreement is valid also at the object-by-object level, with 70-90 per cent of the progenitors cleanly recognised when the parent halo is cleanly recognised itself. Predictions are presented also for quantities that are usually not reproduced by semi-analytic codes, such as the two-point correlation function of the progenitors of massive haloes and the distribution of initial orbital parameters of merging haloes. For the accuracy of the prediction and for the facility with which merger histories are produced, PINOCCHIO provides a means to generate catalogues of DM haloes which is extremely competitive to large-scale N-body simulations, making it a suitable tool for galaxy formation and large-scale structure studies.Comment: 12 pages, 10 eps figures included, submitted to MNRAS. PINOCCHIO is available at http://www.daut.univ.trieste.it/pinocchi
Aims. We studied the star formation rate (SFR) in cosmological hydrodynamical simulations of galaxy (proto-)clusters in the redshift range 0 < z < 4, comparing them to recent observational studies; we also investigated the effect of varying the parameters of the star formation model on galaxy properties such as SFR, star-formation efficiency, and gas fraction. Methods. We analyse a set of zoom-in cosmological hydrodynamical simulations centred on 12 clusters. The simulations are carried out with the GADGET-3 Tree-PM smoothed-particle hydro-dynamics code which includes various subgrid models to treat unresolved baryonic physics, including AGN feedback. Results. Simulations do not reproduce the high values of SFR observed within protocluster cores, where the values of SFR are underpredicted by a factor ≳4 both at z ∼ 2 and z ∼ 4. The difference arises as simulations are unable to reproduce the observed starburst population and is greater at z ∼ 2 because simulations underpredict the normalisation of the main sequence (MS) of star forming galaxies (i.e. the correlation between stellar mass and SFR) by a factor of ∼3. As the low normalisation of the MS seems to be driven by an underestimated gas fraction, it remains unclear whether numerical simulations miss starburst galaxies due to overly underpredicted gas fractions or overly low star formation efficiencies. Our results are stable against varying several parameters of the star formation subgrid model and do not depend on the details of AGN feedback. Conclusions. The subgrid model for star formation, introduced to reproduce the self-regulated evolution of quiescent galaxies, is not suitable to describe violent events like high-redshift starbursts. We find that this conclusion holds, independently of the parameter choice for the star formation and AGN models. The increasing number of multi-wavelength high-redshift observations will help to improve the current star formation model, which is needed to fully recover the observed star formation history of galaxy clusters.
ExaNest is one of three European projects that support a ground-breaking computing architecture for exascale-class systems built upon power-efficient 64-bit ARM processors. This group of projects share an 'everything-close' and 'share-anything' paradigm, which trims down the power consumption - by shortening the distance of signals for most data transfers - as well as the cost and footprint area of the installation - by reducing the number of devices needed to meet performance targets. In ExaNeSt, we will design and implement: (i) a physical rack prototype and its liquid-cooling subsystem providing ultra-dense compute packaging, (ii) a storage architecture with distributed (in-node) non-volatile memory (NVM) devices, (iii) a unified, low-latency interconnect, designed to efficiently uphold desired Quality-of-Service guarantees for a mix of storage with inter-processor flows, and (iv) efficient rack-level memory sharing, where each page is cacheable at only a single node . Our target is to test alternative storage and interconnect options on actual hardware, using real-world HPC applications. The ExaNeSt consortium brings together technology, skills, and knowledge across the entire value chain, from computing IP, packaging, and system deployment, all the way up to operating systems, storage, HPC, big data frameworks, and cutting-edge applications
Context. The correlations between the properties of the brightest cluster galaxy (BCG) and the mass of its central super-massive black hole (SMBH) have been extensively studied from a theoretical and observational angle. More recently, relations connecting the SMBH mass and global properties of the hosting cluster, such as temperature and mass, were observed. Aims. We investigate the correlation between SMBH mass and cluster mass and temperature, their establishment and evolution. We compare their scatter to that of the classical M BH − M BCG relation. Moreover, we study how gas accretion and BH-BH mergers contribute to SMBH growth across cosmic time. Methods. We employed 135 groups and clusters with a mass range 1.4 × 10 13 M − 2.5 × 10 15 M extracted from a set of 29 zoom-in cosmological hydro-dynamical simulations where the baryonic physics is treated with various sub-grid models, including feedback by active galactic nuclei. Results. In our simulations we find that M BH correlates well with M 500 and T 500 , with the scatter around these relations compatible within 2σ with the scatter around M BH − M BCG at z = 0. The M BH − M 500 relation evolves with time, becoming shallower at lower redshift as a direct consequence of hierarchical structure formation. On average, in our simulations the contribution of gas accretion to the total SMBH mass dominates for the majority of the cosmic time (z > 0.4), while in the last 2 Gyr the BH-BH mergers become a larger contributor. During this last process, substructures hosting SMBHs are disrupted in the merger process with the BCG and the unbound stars enrich the diffuse stellar component rather than increase BCG mass. Conclusions. From the results obtained in our simulations with simple sub-grid models we conclude that the scatter around the M BH − T 500 relation is comparable to the scatter around the M BH − M BCG relation and that, given the observational difficulties related to the estimation of the BCG mass, clusters temperature and mass can be a useful proxy for the SMBHs mass, especially at high redshift.
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