K. Dolag

The Astronomical Observatory of Brera, Merate, Lombardy, Italy

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Publications (286)980.04 Total impact

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    ABSTRACT: Giant Radio Halos (RH) are diffuse, Mpc-sized, synchrotron radio sources observed in a fraction of merging galaxy clusters. The current scenario for the origin of RHs assumes that turbulence generated during cluster mergers re-accelerates pre-existing fossil and/or secondary electrons in the intra-cluster-medium (ICM) to the energies necessary to produce the observed radio emission. Moreover, more relaxed clusters could host diffuse "off state" halos produced by secondary electrons. In this Chapter we use Monte Carlo simulations, that combine turbulent-acceleration physics and the generation of secondaries in the ICM, to calculate the occurrence of RHs in the Universe, their spectral properties and connection with properties of the hosting clusters. Predictions for SKA1 surveys are presented at low (100-300 MHz) and mid (1-2 GHz) frequencies assuming the expected sensitivities and spatial resolutions of SKA1. SKA1 will step into an unexplored territory allowing us to study the formation and evolution of RHs in a totally new range of cluster masses and redshift, allowing firm tests of the current theoretical hypothesis. In particular, the combination of SKA1-LOW and SUR will allow the discovery of ~1000 ultrasteep- spectrum halos and to detect for the very first time "off state" RHs. We expect that at least ~2500 giant RHs will be discovered by SKA1-LOW surveys up to z~0.6. Remarkably these surveys will be sensitive to RHs in a cluster mass range (down to ~10^14 solar masses) and redshifts (up to ~1) that are unexplored by current observations. SKA1 surveys will be highly competitive with present and future SZ-surveys in the detection of high-redshift massive objects.
    12/2014;
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    ABSTRACT: We present constraints on the origins of fast radio bursts (FRBs) using one of the largest currently available cosmological hydrodynamic simulations. We use these simulations to calculate contributions to the dispersion measures (DMs) of FRBs from the Milky Way, from the local Universe out to ~100Mpc, from cosmological large-scale structure and from potential FRB host galaxies, and we then compare the results of these simulations to the DMs for observed FRBs. We find that the foreground Milky Way contribution has previously been underestimated by a factor of ~2, and that the the distribution of foreground-subtracted DMs is consistent with a cosmological origin, corresponding to a population of sources observable out to a maximum redshift z~0.6-0.9. We consider models for the spatial distribution and occurrence of FRBs in which they are randomly distributed in the Universe, track the star-formation rate of their host galaxies, track total stellar mass, or require the presence of a central supermassive black hole. While the current data (nine extragalactic FRBs) do not allow us to distinguish between these possibilities, we show that the predicted distributions of DM for these different models will differ considerably once we begin detecting significant fractions of FRBs at higher DMs and higher redshifts. We additionally consider the distribution of fluences for observed FRBs, and show that the observations are consistent with the hypothesis that FRBs are standard candles, each burst producing the same radiated isotropic energy. Comparing the combined DM and fluence distributions with our cosmological model, we find that the data are consistent with a constant isotropic burst energy of ~4e40 erg if FRBs are embedded in host galaxies, or two times higher if FRBs are randomly distributed over the cosmic volume. (abridged)
    12/2014;
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    ABSTRACT: We present results of cosmological simulations of disk galaxies carried out with the GADGET-3 TreePM+SPH code, where star formation and stellar feedback are described using our MUlti Phase Particle Integrator (MUPPI) model. This description is based on simple multi-phase 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 SNe 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 over-production of stars. We use two sets of zoomed-in initial conditions of isolated cosmological halos with masses (2-3) * 10^{12} Msun, both available at several resolution levels. In all cases we obtain spiral galaxies with small bulge-over-total stellar mass ratios (B/T \approx 0.2), extended stellar and gas disks, 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 disk 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. (2010) at a 3 sigma level, thus indicating that our stellar disks 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.
    11/2014; 447(1).
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    ABSTRACT: The ESA's Planck satellite, dedicated to studying the early Universe and its subsequent evolution, was launched 14 May 2009 and has been scanning the microwave and submillimetre sky continuously since 12 August 2009. This paper gives an overview of the mission and its performance, the processing, analysis, and characteristics of the data, the scientific results, and the science data products and papers in the release. The science products include maps of the CMB and diffuse extragalactic foregrounds, a catalogue of compact Galactic and extragalactic sources, and a list of sources detected through the SZ effect. The likelihood code used to assess cosmological models against the Planck data and a lensing likelihood are described. Scientific results include robust support for the standard six-parameter LCDM model of cosmology and improved measurements of its parameters, including a highly significant deviation from scale invariance of the primordial power spectrum. The Planck values for these parameters and others derived from them are significantly different from those previously determined. Several large-scale anomalies in the temperature distribution of the CMB, first detected by WMAP, are confirmed with higher confidence. Planck sets new limits on the number and mass of neutrinos, and has measured gravitational lensing of CMB anisotropies at greater than 25 sigma. Planck finds no evidence for non-Gaussianity in the CMB. Planck's results agree well with results from the measurements of baryon acoustic oscillations. Planck finds a lower Hubble constant than found in some more local measures. Some tension is also present between the amplitude of matter fluctuations derived from CMB data and that derived from SZ data. The Planck and WMAP power spectra are offset from each other by an average level of about 2% around the first acoustic peak.
    Astronomy and Astrophysics 11/2014; 571(A1):1. · 5.08 Impact Factor
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    ABSTRACT: The polarized thermal emission from Galactic dust is the main foreground present in measurements of the polarization of the cosmic microwave background (CMB) at frequencies above 100GHz. We exploit the Planck HFI polarization data from 100 to 353GHz to measure the dust angular power spectra $C_\ell^{EE,BB}$ over the range $40<\ell<600$. These will bring new insights into interstellar dust physics and a precise determination of the level of contamination for CMB polarization experiments. We show that statistical properties of the emission can be characterized over large fractions of the sky using $C_\ell$. For the dust, they are well described by power laws in $\ell$ with exponents $\alpha^{EE,BB}=-2.42\pm0.02$. The amplitudes of the polarization $C_\ell$ vary with the average brightness in a way similar to the intensity ones. The dust polarization frequency dependence is consistent with modified blackbody emission with $\beta_d=1.59$ and $T_d=19.6$K. We find a systematic ratio between the amplitudes of the Galactic $B$- and $E$-modes of 0.5. We show that even in the faintest dust-emitting regions there are no "clean" windows where primordial CMB $B$-mode polarization could be measured without subtraction of dust emission. Finally, we investigate the level of dust polarization in the BICEP2 experiment field. Extrapolation of the Planck 353GHz data to 150GHz gives a dust power $\ell(\ell+1)C_\ell^{BB}/(2\pi)$ of $1.32\times10^{-2}\mu$K$_{CMB}^2$ over the $40<\ell<120$ range; the statistical uncertainty is $\pm0.29$ and there is an additional uncertainty (+0.28,-0.24) from the extrapolation, both in the same units. This is the same magnitude as reported by BICEP2 over this $\ell$ range, which highlights the need for assessment of the polarized dust signal. The present uncertainties will be reduced through an ongoing, joint analysis of the Planck and BICEP2 data sets.
    09/2014;
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    ABSTRACT: We present a new prescription for the small-scale magnetic field of the Milky Way and complement existing models for the total Galactic magnetic field. In particular, we extend the random and striated magnetic field components of the Jansson & Farrar (JF12) model and investigate the characteristics of random magnetic fluctuations. Thereby the small-scale magnetic field is modelled by Gaussian random fields using a random magnetic field power spectrum. We update the spatial distribution of Galactic cosmic ray electron density by a recent GALPROP model. We derive full-sky projections of the total and polarized synchrotron intensity as well as the Faraday rotation measure distribution of our model and compare to real data. We obtain good agreement to the WMAP7 22 GHz polarized and total intensity emission maps and we retrieve improved fits to Galactic foreground rotation measure maps and power spectra of Oppermann et al. Our new prescription significantly complements previous models of the GMF and reveals implications for future studies on the deflection of ultra high energy cosmic rays (UHECR).
    09/2014;
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    ABSTRACT: In large scale cosmological hydrodynamic simulations simplified sub-grid models for gas accretion onto black holes and AGN feedback are commonly used. Such models typically depend on various free parameters, which are not well constrained. We present a new advanced model containing a more detailed description of AGN feedback, where those parameters reflect the results of recent observations. The model takes the dependency of these parameters on the black hole properties into account and describes a continuous transition between the feedback processes acting in the so-called radio-mode and quasar-mode. In addition, we implement a more detailed description of the accretion of gas onto black holes by distinguishing between hot and cold gas accretion. Our new implementations prevent black holes from gaining too much mass, particularly at low redshifts so that our simulations are now very successful in reproducing the observed present-day black hole mass function. Our new model also suppresses star formation in massive galaxies more efficiently than many state-of-the-art models. Therefore, the simulations that include our new implementations produce a more realistic population of quiescent and star-forming galaxies compared to recent observations, even if some discrepancies remain. In addition, the baryon conversion efficiencies in our simulation are consistent with observations presented in literature over the mass range resolved by our simulations. Finally, we discuss the significant impact of the feedback model on the low-luminous end of the AGN luminosity function.
    09/2014;
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    ABSTRACT: Analyses of cosmological hydrodynamic simulations of galaxy clusters suggest that X-ray masses can be underestimated by 10%-30%. The largest bias originates from both violation of hydrostatic equilibrium (HE) and an additional temperature bias caused by inhomogeneities in the X-ray-emitting intracluster medium (ICM). To elucidate this large dispersion among theoretical predictions, we evaluate the degree of temperature structures in cluster sets simulated either with smoothed-particle hydrodynamics (SPH) or adaptive-mesh refinement (AMR) codes. We find that the SPH simulations produce larger temperature variations connected to the persistence of both substructures and their stripped cold gas. This difference is more evident in nonradiative simulations, whereas it is reduced in the presence of radiative cooling. We also find that the temperature variation in radiative cluster simulations is generally in agreement with that observed in the central regions of clusters. Around R 500 the temperature inhomogeneities of the SPH simulations can generate twice the typical HE mass bias of the AMR sample. We emphasize that a detailed understanding of the physical processes responsible for the complex thermal structure in ICM requires improved resolution and high-sensitivity observations in order to extend the analysis to higher temperature systems and larger cluster-centric radii.
    The Astrophysical Journal 07/2014; 791(2):96. · 6.73 Impact Factor
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    Conference Paper: Splotch on the Xeon Phi
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    ABSTRACT: The management and analysis of modern large-scale datasets generated by scientific experiments (observations or numerical simulations) can be very challenging due to continuously increasing sizes and complexity. Traditional data mining and analysis methods can be expensive if applied to large-scale datasets. Visual exploration and discovery can represent invaluable tools providing scientists with prompt and intuitive insights, enabling them to identify characteristics and manageable regions of interest for applying time consuming methods. They can also be effective means for communicating scientific results not only to researchers but also to members of the general public. Splotch [1] is a rendering algorithm for large-scale datasets exploiting modern High Performance Computing (HPC) architectures. Parallelism on HPC systems is achieved by deploying the MPI [2], OpenMP and CUDA paradigms [3]. In order to address emerging technologies and exploit all potential hardware within a HPC environment the algorithm is extended, building upon the MPI and OpenMP implementations, to create an offloading model exploiting Intel’s Xeon Phi using the new Many Integrated Core (MIC) architecture and the provided C++ offload extensions.
    International Supercomputing Conference, Leipzig, Germany; 06/2014
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    ABSTRACT: Analyses of cosmological hydrodynamic simulations of galaxy clusters suggest that X-ray masses can be underestimated by 10% to 30%. The largest bias originates by both violation of hydrostatic equilibrium and an additional temperature bias caused by inhomogeneities in the X-ray emitting intra-cluster medium (ICM). To elucidate on this large dispersion among theoretical predictions, we evaluate the degree of temperature structures in cluster sets simulated either with smoothed-particle-hydrodynamics (SPH) and adaptive-mesh-refinement (AMR) codes. We find that the SPH simulations produce larger temperature variations connected to the persistence of both substructures and their stripped cold gas. This difference is more evident in no-radiative simulations, while it is reduced in the presence of radiative cooling. We also find that the temperature variation in radiative cluster simulations is generally in agreement with the observed one in the central regions of clusters. Around R_500 the temperature inhomogeneities of the SPH simulations can generate twice the typical hydrostatic-equilibrium mass bias of the AMR sample. We emphasize that a detailed understanding of the physical processes responsible for the complex thermal structure in ICM requires improved resolution and high sensitivity observations in order to extend the analysis to higher temperature systems and larger cluster-centric radii.
    06/2014;
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    ABSTRACT: Splotch is a rendering algorithm for exploration and visual discovery in particle-based datasets coming from astronomical observations or numerical simulations. The strengths of the approach are production of high quality imagery and support for very large-scale datasets through an effective mix of the OpenMP and MPI parallel programming paradigms. This article reports our experiences in re-designing Splotch for exploiting emerging HPC architectures nowadays increasingly populated with GPUs. A performance model is introduced to guide our re-factoring of Splotch. A number of parallelization issues are discussed, in particular relating to race conditions and workload balancing, towards achieving optimal performances. Our implementation was accomplished by using the CUDA programming paradigm. Our strategy is founded on novel schemes achieving optimised data organisation and classification of particles. We deploy a reference cosmological simulation to present performance results on acceleration gains and scalability. We finally outline our vision for future work developments including possibilities for further optimisations and exploitation of hybrid systems and emerging accelerators.
    Astronomy and Computing. 04/2014; 5:9-18.
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    ABSTRACT: A VLA Sky Survey of the extragalactic sky at S band (2-4 GHz) with polarization information can uniquely probe the magneto-ionic medium in a wide range of astrophysical environments over cosmic time. For a shallow all-sky survey, we expect to detect over 4 million sources in total intensity $>$ 0.45 mJy beam$^{-1}$ and over 2.2$\times$10$^5$ sources in polarized intensity. With these new observations, we expect to discover new classes of polarized radio sources in very turbulent astrophysical environments and those with extreme values of Faraday depth. Moreover, by determining reliable Faraday depths and by modeling depolarization effects, we can derive properties of the magneto-ionic medium associated with AGNs, absorption line systems and galaxies, addressing the following unresolved questions: (1) What is the covering fraction, the degree of turbulence and the origin of absorption line systems? (2) What is the thermal content in AGNs and radio galaxies? (3) How do AGNs and galaxies evolve over cosmic time? (4) What causes the increase in percentage polarization with decreasing flux densities at the low flux density end of the polarized source count? (5) What is the growth rate of large-scale magnetic fields in galaxies?
    01/2014;
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    ABSTRACT: We study the role of feedback from supernovae and black holes in the evolution of the star formation rate function (SFRF) of $z\sim4-7$ galaxies. We use a new set of cosmological hydrodynamic simulations, ANGUS (AustraliaN GADGET-3 early Universe Simulations), run with a modified and improved version of the parallel TreePM-smoothed particle hydrodynamics code GADGET-3 called P-GADGET3(XXL), that includes a self-consistent implementation of stellar evolution and metal enrichment. In our simulations both Supernova (SN) driven galactic winds and Active Galactic Nuclei (AGN) act simultaneously in a complex interplay. The SFRF is insensitive to feedback prescription at $z>5$, meaning that it cannot be used to discriminate between feedback models during reionisation. However, the SFRF is sensitive to the details of feedback prescription at lower redshift. By exploring different SN driven wind velocities and regimes for the AGN feedback, we find that the key factor for reproducing the observed SFRFs is a combination of "strong" SN winds and early AGN feedback in low mass galaxies. Conversely, we show that the choice of initial mass function and inclusion of metal cooling have less impact on the evolution of the SFRF. When variable winds are considered, we find that a non-aggressive wind scaling is needed to reproduce the SFRFs at $z\ge4$. Otherwise, the amount of objects with low SFRs is greatly suppressed and at the same time winds are not effective enough in the most massive systems.
    12/2013;
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    ABSTRACT: The adiabatic evolution of the temperature of the cosmic microwave background (CMB) is a key prediction of standard cosmology. We study deviations from the expected adiabatic evolution of the CMB temperature of the form $T(z) =T_0(1+z)^{1-\alpha}$ using measurements of the spectrum of the Sunyaev Zel'dovich Effect with the South Pole Telescope (SPT). We present a method for using the ratio of the Sunyaev Zel'dovich signal measured at 95 and 150 GHz in the SPT data to constrain the temperature of the CMB. We demonstrate that this approach provides unbiased results using mock observations of clusters from a new set of hydrodynamical simulations. We apply this method to a sample of 158 SPT-selected clusters, spanning the redshift range $0.05 < z < 1.35$, and measure $\alpha = 0.017^{+0.030}_{-0.028}$, consistent with the standard model prediction of $\alpha=0$. In combination with other published results, we constrain $\alpha = 0.011 \pm 0.016$, an improvement of $\sim 20\%$ over published constraints. This measurement also provides a strong constraint on the effective equation of state in models of decaying dark energy $w_\mathrm{eff} = -0.987^{+0.016}_{-0.017}$.
    Monthly Notices of the Royal Astronomical Society 12/2013; 440(3). · 5.52 Impact Factor
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    ABSTRACT: We study the role of feedback from supernovae and black holes in the evolution of the star formation rate function (SFRF) of z~4-7 galaxies. We use a new set of cosmological hydrodynamic simulations, ANGUS (AustraliaN GADGET-3 early Universe Simulations), run with a modified and improved version of the parallel TreePM-smoothed particle hydrodynamics code GADGET-3 called P-GADGET3(XXL), that includes a self-consistent implementation of stellar evolution and metal enrichment. In our simulations both Supernova (SN) driven galactic winds and Active Galactic Nuclei (AGN) act simultaneously in a complex interplay. The SFRF is insensitive to feedback prescription at z>5, meaning that it cannot be used to discriminate between feedback models during reionisation. However, the SFRF is sensitive to the details of feedback prescription at lower redshift. By exploring different SN driven wind velocities and regimes for the AGN feedback, we find that the key factor for reproducing the observed SFRFs is a combination of "strong" SN winds and early AGN feedback in low mass galaxies. Conversely, we show that the choice of initial mass function and inclusion of metal cooling have less impact on the evolution of the SFRF. When variable winds are considered, we find that a non-aggressive wind scaling is needed to reproduce the SFRFs at z>4. Otherwise, the amount of objects with low SFRs is greatly suppressed and at the same time winds are not effective enough in the most massive systems.
    12/2013; 438(4).
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    ABSTRACT: We present the first all-sky sample of galaxy clusters detected blindly by the Planck satellite through the Sunyaev-Zeldovich (SZ) effect from its six highest frequencies. This Early SZ (ESZ) sample of 189 candidates comprises high signal-to-noise clusters, from 6 to 29. Its high reliability (purity above 95%) is further insured by an extensive validation process based on Planck-internal quality assessments and external cross-identification and follow-up observations. Planck provides the first measured SZ signal for about 80% of the 169 ESZ known clusters. Planck further releases 30 new cluster candidates among which 20 are within the ESZ signal-to-noise selection criterion. Eleven of these 20 ESZ candidates are confirmed using XMM-Newton snapshot observations as new clusters, most of them with disturbed morphologies and low luminosities. The ESZ clusters are mostly at moderate redshifts (86% with z below 0.3) and span over a decade in mass, up to the rarest and most massive clusters with masses above 10^15 Msol.
    11/2013;
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    ABSTRACT: The performance of the Planck instruments in space is enabled by their low operating temperatures, 20K for LFI and 0.1K for HFI, achieved through a combination of passive radiative cooling and three active mechanical coolers. Active coolers were chosen to minimize straylight on the detectors and to maximize lifetime. The scientific requirement for very broad frequency led to two detector technologies with widely different temperature and cooling needs. This made use of a helium cryostat, as used by previous cryogenic space missions (IRAS, COBE, ISO, SPITZER, AKARI), infeasible. Radiative cooling is provided by three V-groove radiators and a large telescope baffle. The active coolers are a hydrogen sorption cooler (<20K), a 4He Joule-Thomson cooler (4.7K), and a 3He-4He dilution cooler (1.4K and 0.1K). The flight system was at ambient temperature at launch and cooled in space to operating conditions. The bolometer plate of the High Frequency Instrument reached 93mK on 3 July 2009, 50 days after launch. The solar panel always faces the Sun, shadowing the rest of Planck, and operates at a mean temperature of 384K. At the other end of the spacecraft, the telescope baffle operates at 42.3K and the telescope primary mirror operates at 35.9K. The temperatures of key parts of the instruments are stabilized by both active and passive methods. Temperature fluctuations are driven by changes in the distance from the Sun, sorption cooler cycling and fluctuations in gas-liquid flow, and fluctuations in cosmic ray flux on the dilution and bolometer plates. These fluctuations do not compromise the science data.
    11/2013;
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    ABSTRACT: We present the XMM-Newton follow-up for validation of Planck cluster candidates. Twenty-five candidates have been observed to date using snapshot (~10 ksec) exposures: ten as part of a pilot programme to sample a low range of signal-to-noise ratios (45 candidates. The sensitivity and spatial resolution of XMM-Newton allows unambiguous discrimination between clusters and false candidates. A total of 21 candidates are confirmed as extended X-ray sources. Seventeen are single clusters, the majority of which are found to have highly irregular and disturbed morphologies. The remaining four sources are multiple systems, including the unexpected discovery of a supercluster at z=0.45. For most of the sources we are able to derive a redshift estimate from the X-ray Fe K line (albeit of variable quality). The new clusters span the redshift range 0.09 <~ z <~ 0.54 with a median redshift of z ~ 0.37. A first estimate is made of their X-ray properties including the characteristic size, which is used to improve the SZ Compton parameter estimate. The validation programme has helped to optimise the Planck candidate selection process. It has also provided a preview of the X-ray properties of these newly-discovered clusters, allowing comparison to their SZ properties, and to the X-ray and SZ properties of known clusters observed in the Planck survey. Our results suggest that Planck may have started to reveal a non-negligible population of massive dynamically perturbed objects that is under-represented in X-ray surveys. However, despite their particular properties, these new clusters appear to follow the Ysz-Yx relation established for X-ray selected objects.
    11/2013;
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    ABSTRACT: We present an analysis of the properties of the 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, one of which also accounts for the effect of feedback from AGN resulting from gas accretion onto super-massive 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 that are in good agreement with X-ray observations at all mass scales. However, our simulations are not able to account for the observed diversity between CC and NCC clusters: 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 NCC 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 halos into the inter-galactic 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.
    Monthly Notices of the Royal Astronomical Society 11/2013; · 5.52 Impact Factor

Publication Stats

5k Citations
980.04 Total Impact Points

Institutions

  • 2007–2014
    • The Astronomical Observatory of Brera
      Merate, Lombardy, Italy
  • 2013
    • Max Planck Institute for Extraterrestrial Physics
      Arching, Bavaria, Germany
  • 2012–2013
    • Ludwig-Maximilian-University of Munich
      • Department of Physics
      München, Bavaria, Germany
  • 2004–2012
    • Max Planck Institute for Astrophysics
      Arching, Bavaria, Germany
    • INFN - Istituto Nazionale di Fisica Nucleare
      Frascati, Latium, Italy
  • 2011
    • University of Turku
      Turku, Province of Western Finland, Finland
  • 2010
    • Stanford University
      Palo Alto, California, United States
  • 2008
    • University of California, Santa Cruz
      Santa Cruz, California, United States
  • 2003–2008
    • University of Padova
      Padua, Veneto, Italy
  • 2005
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2004–2005
    • University of Bologna
      • Department of Physics and Astronomy DIFA
      Bologna, Emilia-Romagna, Italy
  • 2002
    • University of Pennsylvania
      • Department of Physics and Astronomy
      Philadelphia, Pennsylvania, United States