ALBERT

Description: 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 k max ~ 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.

Description: Achieving a robust determination of the gas density profile in the outskirts of clusters is a crucial step for measuring their baryonic content and using them as cosmological probes. The difficulty in obtaining this measurement lies not only in the low surface brightness of the intracluster medium (ICM), but also in the inhomogeneities of the gas associated with clumps, asymmetries and accretion patterns. Using a set of hydrodynamical simulations of 62 galaxy clusters and groups we study these kinds of inhomogeneities, focusing on the ones on large scales, which, unlike clumps, are difficult to identify. For this purpose we introduce the concept of the residual clumpiness , C R , which quantifies the large-scale inhomogeneity of the ICM. After showing that this quantity can be robustly defined for relaxed systems, we characterize how it varies with radius, and with the mass and dynamical state of the halo. Most importantly, we observe that it introduces an overestimate in the determination of the density profile from the X-ray emission, which translates into a systematic overestimate of 6 (12) per cent in the measurement of M gas at R 200 for our relaxed (perturbed) cluster sample. At the same time, the increase of C R with radius introduces a ~2 per cent systematic underestimate in the measurement of the hydrostatic-equilibrium mass ( M he ), which adds to the previous one, generating a systematic overestimate of ~8.5 per cent in f gas in our relaxed sample. Because the residual clumpiness of the ICM is not directly observable, we study its correlation with the azimuthal scatter in the X-ray surface brightness of the halo, a quantity that is well constrained by current measurements, and in the y -parameter profiles, which will be obtained in the forthcoming Sunyaev–Zeldovich (SZ) experiments. We find that their correlation is highly significant ( r S  = 0.6–0.7), allowing us to define the azimuthal scatter measured in the X-ray surface brightness profile and in the y -parameter as robust proxies of C R . After providing a function that connects the two quantities, we find that correcting the observed gas density profiles using the azimuthal scatter eliminates the bias in the measurement of M gas for relaxed objects, which becomes 0 ± 2 per cent up to 2 R 200 , and reduces it by a factor of 3 for perturbed ones. This method also allows us to eliminate the systematics on the measurements of M he and f gas , although a significant halo-to-halo scatter remains.

Description: We carry out an analysis of a set of cosmological smoothed particle hydrodynamics (SPH) hydrodynamical simulations of galaxy clusters and groups aimed at studying the total baryon budget in clusters, and how this budget is shared between the hot diffuse component and the stellar component. Using the TreePM+SPH gadget-3 code, we carried out one set of non-radiative simulations, and two sets of simulations including radiative cooling, star formation and feedback from supernovae (SNe), one of which also accounting for the effect of feedback from active galactic nuclei (AGN). The analysis is carried out with the twofold aim of studying the implication of stellar and hot gas content on the relative role played by SNe and AGN feedback, and to calibrate the cluster baryon fraction and its evolution as a cosmological tool. With respect to previous similar analysis, the simulations used in this study provide us with a sufficient statistics of massive objects and including an efficient AGN feedback. We find that both radiative simulation sets predict a trend of stellar mass fraction with cluster mass that tends to be weaker than the observed one. However this tension depends on the particular set of observational data considered. Including the effect of AGN feedback alleviates this tension on the stellar mass and predicts values of the hot gas mass fraction and total baryon fraction to be in closer agreement with observational results. We further compute the ratio between the cluster baryon content and the cosmic baryon fraction, Y b , as a function of clustercentric radius and redshift. At R 500 we find for massive clusters with M 500  〉 2  x 10 14 h –1 M that Y b is nearly independent of the physical processes included and characterized by a negligible redshift evolution: Y b, 500  = 0.85 ± 0.03 with the error accounting for the intrinsic rms scatter within the set of simulated clusters. At smaller radii, R 2500 , the typical value of Y b slightly decreases, by an amount that depends on the physics included in the simulations, while its scatter increases by about a factor of 2. These results have interesting implications for the cosmological applications of the baryon fraction in clusters.

Description: We present an analysis of the properties of the intracluster medium (ICM) in an extended set of cosmological hydrodynamical simulations of galaxy clusters and groups performed with the treepm + sph gadget-3 code. Besides a set of non-radiative simulations, we carried out two sets of simulations including radiative cooling, star formation, metal enrichment and feedback from supernovae (SNe), one of which also accounts for the effect of feedback from active galactic nuclei (AGN) resulting from gas accretion on to supermassive black holes. These simulations are analysed with the aim of studying the relative role played by SN and AGN feedback on the general properties of the diffuse hot baryons in galaxy clusters and groups: scaling relations, temperature, entropy and pressure radial profiles, and ICM chemical enrichment. We find that simulations including AGN feedback produce scaling relations between X-ray observable quantities that are in good agreement with observations at all mass scales. Observed pressure profiles are also shown to be quite well reproduced in our radiative simulations, especially when AGN feedback is included. However, our simulations are not able to account for the observed diversity between cool-core and non-cool-core clusters, as revealed by X-ray observations: unlike for observations, we find that temperature and entropy profiles of relaxed and unrelaxed clusters are quite similar and resemble more the observed behaviour of non-cool-core clusters. As for the pattern of metal enrichment, we find that an enhanced level of iron abundance is produced by AGN feedback with respect to the case of purely SN feedback. As a result, while simulations including AGN produce values of iron abundance in groups in agreement with observations, they over-enrich the ICM in massive clusters. The efficiency of AGN feedback in displacing enriched gas from haloes into the intergalactic medium at high redshift also creates a widespread enrichment in the outskirts of clusters and produces profiles of iron abundance whose slope is in better agreement with observations. By analysing the pattern of the relative abundances of silicon and iron and the fraction of metals in the stellar phase, our results clearly show that different sources of energy feedback leave different imprints in the enrichment pattern of the hot ICM and stars. Our results confirm that including AGN feedback goes in the right direction of reconciling simulation predictions and observations for several observational ICM properties. Still a number of important discrepancies highlight that the model still needs to be improved to produce the correct interplay between cooling and feedback in central cluster regions.

Description: By means of zoom-in hydrodynamic simulations, we quantify the amount of neutral hydrogen (H i ) hosted by groups and clusters of galaxies. Our simulations, which are based on an improved formulation of smoothed particle hydrodynamics, include radiative cooling, star formation, metal enrichment and supernova feedback, and can be split into two different groups, depending on whether feedback from active galactic nuclei (AGN) is turned on or off. Simulations are analysed to account for H i self-shielding and the presence of molecular hydrogen. We find that the mass in neutral hydrogen of dark matter haloes monotonically increases with the halo mass and can be well described by a power law of the form $M_{\rm H\,\small {I}}(M,z)\propto M^{3/4}$ . Our results point out that AGN feedback reduces both the total halo mass and its H i mass, although it is more efficient in removing H i . We conclude that AGN feedback reduces the neutral hydrogen mass of a given halo by ~50 per cent, with a weak dependence on halo mass and redshift. The spatial distribution of neutral hydrogen within haloes is also affected by AGN feedback, whose effect is to decrease the fraction of H i that resides in the halo inner regions. By extrapolating our results to haloes not resolved in our simulations, we derive astrophysical implications from the measurements of $\Omega _{\rm H\,\small {I}}(z)$ : haloes with circular velocities larger than ~25 km s –1 are needed to host H i in order to reproduce observations. We find that only the model with AGN feedback is capable of reproducing the value of $\Omega _{\rm H\,\small {I}}b_{\rm H\,\small {I}}$ derived from available 21 cm intensity mapping observations.

Description: The large-scale distribution of galaxies and galaxy clusters in the universe can be described in the mathematical language of multifractal sets. A particularly significant aspect of this description is that it furnishes a natural explanation for the observed differences in clustering properties of objects of different density in terms of multiscaling, the generic consequence of the application of a local density threshold to a multifractal set. The multiscaling hypothesis suggests ways of improving upon the traditional statistical measures of clustering pattern (correlation functions) and exploring further the connection between clustering pattern and dynamics.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Martinez, V J -- Paredes, S -- Borgani, S -- Coles, P -- New York, N.Y. -- Science. 1995 Sep 1;269(5228):1245-7.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17732110" target="_blank"〉PubMed〈/a〉

Description: We present an implementation of smoothed particle hydrodynamics (SPH) with improved accuracy for simulations of galaxies and the large-scale structure. In particular, we implement and test a vast majority of SPH improvement in the developer version of gadget -3. We use the Wendland kernel functions, a particle wake-up time-step limiting mechanism and a time-dependent scheme for artificial viscosity including high-order gradient computation and shear flow limiter. Additionally, we include a novel prescription for time-dependent artificial conduction, which corrects for gravitationally induced pressure gradients and improves the SPH performance in capturing the development of gas-dynamical instabilities. We extensively test our new implementation in a wide range of hydrodynamical standard tests including weak and strong shocks as well as shear flows, turbulent spectra, gas mixing, hydrostatic equilibria and self-gravitating gas clouds. We jointly employ all modifications; however, when necessary we study the performance of individual code modules. We approximate hydrodynamical states more accurately and with significantly less noise than standard gadget -SPH. Furthermore, the new implementation promotes the mixing of entropy between different fluid phases, also within cosmological simulations. Finally, we study the performance of the hydrodynamical solver in the context of radiative galaxy formation and non-radiative galaxy cluster formation. We find galactic discs to be colder and more extended and galaxy clusters showing entropy cores instead of steadily declining entropy profiles. In summary, we demonstrate that our improved SPH implementation overcomes most of the undesirable limitations of standard gadget -SPH, thus becoming the core of an efficient code for large cosmological simulations.

Description: 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 (10 000 km s –1 ) increment. We perform hydrodynamical simulations of isolated cluster (total mass 10 14 h –1 M ), which is initially evolved to form a dense cool core, having central T ≤ 10 6  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 10 7 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 Myr.

Description: We present results from multifrequency radiative hydrodynamical chemistry simulations addressing primordial star formation and related stellar feedback from various populations of stars, stellar spectral energy distributions (SEDs) and initial mass functions. Spectra for massive stars, intermediate-mass stars and regular solar-like stars are adopted over a grid of 150 frequency bins and consistently coupled with hydrodynamics, heavy-element pollution and non-equilibrium species calculations. Powerful massive Population III stars are found to be able to largely ionize H and, subsequently, He and He + , causing an inversion of the equation of state and a boost of the Jeans masses in the early intergalactic medium. Radiative effects on star formation rates are between a factor of a few and 1 dex, depending on the SED. Radiative processes are responsible for gas heating and photoevaporation, although emission from soft SEDs has minor impacts. These findings have implications for cosmic gas preheating, primordial direct-collapse black holes, the build-up of ‘cosmic fossils’ such as low-mass dwarf galaxies, the role of active galactic nuclei during reionization, the early formation of extended discs and angular-momentum catastrophe.

Description: We have simulated the formation of a massive galaxy cluster ( $M_{200}^{\rm crit}$ = 1.1 x 10 15 h –1 M ) in a cold dark matter universe using 10 different codes ( ramses , 2 incarnations of arepo and 7 of gadget ), modelling hydrodynamics with full radiative subgrid physics. These codes include smoothed-particle hydrodynamics (SPH), spanning traditional and advanced SPH schemes, adaptive mesh and moving mesh codes. Our goal is to study the consistency between simulated clusters modelled with different radiative physical implementations – such as cooling, star formation and thermal active galactic nucleus (AGN) feedback. We compare images of the cluster at z = 0, global properties such as mass, and radial profiles of various dynamical and thermodynamical quantities. We find that, with respect to non-radiative simulations, dark matter is more centrally concentrated, the extent not simply depending on the presence/absence of AGN feedback. The scatter in global quantities is substantially higher than for non-radiative runs. Intriguingly, adding radiative physics seems to have washed away the marked code-based differences present in the entropy profile seen for non-radiative simulations in Sembolini et al.: radiative physics + classic SPH can produce entropy cores, at least in the case of non cool-core clusters. Furthermore, the inclusion/absence of AGN feedback is not the dividing line -as in the case of describing the stellar content – for whether a code produces an unrealistic temperature inversion and a falling central entropy profile. However, AGN feedback does strongly affect the overall stellar distribution, limiting the effect of overcooling and reducing sensibly the stellar fraction.