Stefano Borgani

Chemical enrichment of galaxy clusters from hydrodynamical simulations

We present cosmological hydrodynamical simulations of galaxy clusters aimed at studying the process of metal enrichment of the intra-cluster medium (ICM). These simulations have been performed by implementing a detailed model of chemical evolution in the TREE-PM+SPM GADGET-2 code. This model allows us to follow the metal release from Type II supernovae (SNII), Type Ia supernovae (SNIa) and asymptotic giant branch (AGB) stars by properly accounting for the lifetimes of stars of different mass, as well as to change the stellar initial mass function (IMF), the lifetime function and the stellar yields. As such, our implementation of chemical evolution represents a powerful instrument to follow the cosmic history of metal production. The simulations presented here have been performed with the twofold aim of checking numerical effects, as well as the impact of changing the model of chemical evolution and the efficiency of stellar feedback. In general, we find that the distribution of metals produced by SNII is more clumpy than for the product of low-mass stars, as a consequence of the different time-scales over which they are released. Using a standard Salpeter IMF produces a radial profile of iron abundance which is in fairly good agreement with observations available out to ≃0.6R 500 . This result holds almost independent of the numerical scheme adopted to distribute metals around star-forming regions. The mean age of enrichment of the ICM corresponds to redshift z ∼ 0.5, which progressively increases outside the virial region. Increasing resolution, we improve the description of a diffuse high-redshift enrichment of the inter-galactic medium (IGM). This turns into a progressively more efficient enrichment of the cluster outskirts, while having a smaller impact at R ≤ 0.5R 500 . As for the effect of the model of chemical evolution, we find that changing the IMF has the strongest impact. Using an IMF, which is top-heavier than the Salpeter one, provides a larger iron abundance, possibly in excess of the observed level, also significantly increasing the [O/Fe] relative abundance. Our simulations always show an excess of low-redshift star formation and, therefore, of the abundance of oxygen in central cluster regions, at variance with observations. This problem is not significantly ameliorated by increasing the efficiency of the stellar feedback.

Minkowski functionals of Abell/ACO clusters

We determine the Minkowski functionals for a sample of Abell/ACO clusters, 401 with measured and 16 with estimated redshifts. The four Minkowski functionals (including the void probability function and the mean genus) deliver a global description of the spatial distribution of clusters on scales from

Scaling in the Universe

10

Constraining cosmological models with cluster power spectra

to

The history of chemical enrichment in the intracluster medium from cosmological simulations

60\hMpc

Non-linear clustering in the cold plus hot dark matter model

with a clear geometric interpretation. Comparisons with mock catalogues of N--body simulations using different variants of the CDM model demonstrate the discriminative power of the description. The standard CDM model and the model with tilted perturbation spectrum cannot generate the Minkowski functionals of the cluster data, while a model with a cosmological constant and a model with breaking of the scale invariance of perturbations (BSI) yield compatible results.

The Epoch of Structure Formation in Blue Mixed Dark Matter Models

Abstract The aim of this review article is to give a comprehensive description of the scaling properties detected for the distribution of cosmic structures, like galaxies and galaxy clusters. I will also discuss the more popular theoretical models, which have been proposed to account for the huge body of observational data. Due to the great variety of statistical methods, developed in the last twenty years to statistically describe the large-scale structure of the Universe, I will mainly concentrate on those methods which reveal remarkable regularities and scaling in the structure of the Universe. Although in most cases I prefer not to enter into the technical aspects of how implementing such methods, more details will be furnished about the description of galaxy clustering in terms of fractal concepts. Statistical methods based on fractal analyses have been recently employed in cosmological context. Despite recent claims for a Universe, which behaves like a fractal at arbitrarily large scales, I will show that the fractal language can be usefully employed to disprove this picture. The emerging scenario is that of a Universe, which behaves like a self-similar structure at small scales, where fractality is dynamically generated by non-linear gravitational clustering, while preserving large-scale homogeneity. Nevertheless, even at scales /s> 10h−1Mpc, where gravity still acts linearly, the distribution of galaxy clusters shows remarkable scale-invariant features, which could give precise hints about the initial conditions for the evolution of the large-scale structure of the Universe.

Large-Scale Structure in Mixed Dark Matter Models with a Nonthermal Volatile Component

Abstract Using extensive N-body simulations we estimate redshift space power spectra of clusters of galaxies for different cosmological models (SCDM, TCDM, CHDM, ΛCDM, OCDM, BSI, τCDM) and compare the results with observational data for Abell–ACO clusters. Our mock samples of galaxy clusters have the same geometry and selection functions as the observational sample which contains 417 clusters of galaxies in a double cone of galactic latitude |b|>30° up to a depth of 240 h −1 Mpc . The power spectrum has been estimated for wave numbers k in the range 0.03≲k≲0.2 h Mpc −1 . For k>k max ≃0.05 h Mpc −1 the power spectrum of the Abell–ACO clusters has a power-law shape, P(k)∝kn, with n≈−1.9, while it changes sharply to a positive slope at k Ω 0 =0.35 are rejected. Better agreement with observation can be found for the ΛCDM model with Ω 0 =0.35 and h=0.7 and the CHDM model with two degenerate neutrinos and Ω HDM =0.2 as well as for a CDM model with broken scale invariance (BSI) and the τCDM model. As for the peak in the Abell–ACO cluster power spectrum, we find that it does not represent a very unusual finding within the set of mock samples extracted from our simulations.

Mass Segregation in Dark Matter Models

The distribution of metals in the intracluster medium (ICM) of galaxy clusters provides valuable information on their formation and evolution, on the connection with the cosmic star formation and on the effects of different gas processes. By analysing a sample of simulated galaxy clusters, we study the chemical enrichment of the ICM, its evolution, and its relation with the physical processes included in the simulation and with the thermal properties of the core. These simulations, consisting of re-simulations of 29 Lagrangian regions performed with an upgraded version of the smoothed particle hydrodynamics (SPH) GADGET-3 code, have been run including two different sets of baryonic physics: one accounts for radiative cooling, star formation, metal enrichment and supernova (SN) feedback, and the other one further includes the effects of feedback from active galactic nuclei (AGN). In agreement with observations, we find an anti-correlation between entropy and metallicity in cluster cores, and similar radial distributions of heavy-element abundances and abundance ratios out to large clustercentric distances (similar to R-180). In the outskirts, namely outside of similar to 0.2 R-180, we find a remarkably homogeneous metallicity distribution, with almost flat profiles of the elements produced by either SNIa or SNII. We investigated the origin of this phenomenon and discovered that it is due to the widespread displacement of metal-rich gas by early (z > 2-3) AGN powerful bursts, acting on small high-redshift haloes. Our results also indicate that the intrinsic metallicity of the hot gas for this sample is on average consistent with no evolution between z = 2 and z = 0, across the entire radial range.

The angular distribution of clusters in skewed CDM models

We use high resolution PM N-body simulations to follow the development of non-linear clustering in a flat Universe, dominated by Cold + Hot Dark Matter (CHDM) with 60% of CDM, 30% of HDM and 10% of baryons; a simulation box of 100 Mpc a side (