Information Architecture Automatization for the Semantic Web

Brunetti, Josep Maria; Garcı́a, Roberto

doi:10.1007/978-3-642-23768-3_45

Cited by 35 publications

(41 citation statements)

References 5 publications

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“…We note, however, that the re-acceleration model proposed in that work is due to Alfen modes, while more recent works indicate that the re-acceleration is due to MHD modes at very small scales (see e.g Brunetti & Lazarian 2011…”

mentioning

confidence: 55%

A non-ideal magnetohydrodynamic gadget: simulating massive galaxy clusters

Bonafede¹,

Dolag²,

Stasyszyn³

et al. 2011

Monthly Notices of the Royal Astronomical Society

118

144

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Magnetic fields in the intra‐cluster medium (ICM) of galaxy clusters have been studied in the past through different methods. So far, our understanding of the origin of these magnetic fields, as well as their role in the process of structure formation and their interplay with the other constituents of the ICM, is still limited. In the coming years, the up‐coming generation of radio telescopes is going to provide new data that will have the potential of setting constraints on the properties of magnetic fields in galaxy clusters. Here, we present zoomed‐in simulations for a set of massive galaxy clusters (Mv ≥ 1015 h−1 M⊙). This is an ideal sample to study the evolution of the magnetic field during the process of structure formation in detail. Turbulent motions of the gas within the ICM will manifest themselves in a macroscopic magnetic resistivity ηm, which has to be taken explicitly into account, especially at scales below the resolution limit. We have adapted the magnetohydrodynamic (MHD) gadget code by Dolag & Stasyszyn to include the treatment of the magnetic resistivity, and for the first time we have included non‐ideal MHD equations to better follow the evolution of the magnetic field within the galaxy clusters. We investigate which value of the magnetic resistivity ηm is required to match the magnetic field profile derived from radio observations. We find that a value of ηm∼ 6 × 1027 cm2 s−1 is necessary to recover the shape of the magnetic field profile inferred from radio observations of the Coma cluster. This value agrees well with the expected level of turbulent motions within the ICM at our resolution limit. The magnetic field profiles of the simulated clusters can be fitted by a β‐model‐like profile, with small dispersion of the parameters. We also find that the temperature, density and entropy profiles of the clusters depend on the magnetic resistivity constant, having flatter profiles in the inner regions when the magnetic resistivity increases.

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mentioning

confidence: 55%

A non-ideal magnetohydrodynamic gadget: simulating massive galaxy clusters

Bonafede¹,

Dolag²,

Stasyszyn³

et al. 2011

Monthly Notices of the Royal Astronomical Society

118

144

View full text Add to dashboard Cite

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“…However, Re scales linearly with the characteristic length of the flow, and large-scale eddies should be captured. We expect that turbulence injection in the ICM happens at scales well above our grid size (L ≈ 100-400 kpc) (Brunetti & Lazarian 2011). What we do capture in this calculation is the kinetic energy associated with bulk random motions of the ICM gas at and above the grid scale of the simulation.…”

Section: Turbulence Kinetic Energymentioning

confidence: 76%

Structure and turbulence in simulated galaxy clusters and the implications for the formation of radio haloes

Hallman¹,

Jeltema²

2011

Monthly Notices of the Royal Astronomical Society

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We track the histories of massive clusters of galaxies formed within a cosmological hydrodynamic simulation. Specifically, we track the time evolution of the energy in random bulk motions of the intracluster medium and X‐ray measures of cluster structure and their relationship to cluster mergers. We aim to assess the viability of the turbulent re‐acceleration model for the generation of giant radio haloes by comparing the level of turbulent kinetic energy in simulated clusters with the observed properties of radio halo clusters, giving particular attention to the association of radio haloes to clusters with disturbed X‐ray structures. The evolution of X‐ray cluster structure and turbulence kinetic energy, k, in simulations can then inform us about the expected lifetime of radio haloes and the fraction of clusters as a function of redshift expected to host them. We find strong statistical correlation of disturbed structure measures and the presence of enhancements in k. Specifically, quantitatively ‘disturbed’, radio halo‐like X‐ray morphology in our sample indicates a 92 per cent chance of the cluster in question having k elevated to more than twice its minimum value over the cluster’s life. The typical lifetime of episodes of elevated turbulence is on the order of 1 Gyr, though these periods can last 5 Gyr or more. This variation reflects the wide range of cluster histories; while some clusters undergo complex and repeated mergers spending a majority of their time in elevated k states, other clusters are relaxed over nearly their entire history. We do not find a bimodal relationship between cluster X‐ray luminosity and the total energy in turbulence that might account directly for a bimodal LX–P1.4 GHz relation. However, our result may be consistent with the observed bimodality, as here we are not including a full treatment of cosmic ray sources and magnetic fields.

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“…In the last decade, observational evidence suggests that they are caused by the continuous acceleration of electrons in turbulent gas (Brunetti et al 2001; Petrosian 2001, Brunetti & Lazarian 2007. In addition, continuous injection of secondary particles through proton-proton collisions (Dennison 1980, Enßlin et al 2011 can also be re-accelerated together with the primary electrons (Brunetti & Lazarian 2011, Pinzke et al 2017) in these regions and may play a role in the generation of radio halos. However, lack of gamma ray detection puts constraints on such a mechanism (e.g., Brunetti et al 2017 and references therein).…”

Section: Introductionmentioning

confidence: 99%

Revived fossil plasma sources in galaxy clusters

Mandal

Intema

Weeren

et al. 2020

A&A

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It is well established that particle acceleration by shocks and turbulence in the intra-cluster medium can produce cluster-scale synchrotron emitting sources. However, the detailed physics of these particle acceleration processes is still not well understood. One of the main open questions is the role of fossil relativistic electrons that have been deposited in the intra-cluster medium by radio galaxies. These synchrotron-emitting electrons are very difficult to study, as their radiative life time is only tens of Myrs at GHz frequencies, and are therefore a relatively unexplored population. Despite the typical steep radio spectrum due to synchrotron losses, these fossil electrons are barely visible even at radio frequencies well below a GHz. However, when a pocket of fossil radio plasma is compressed, it boosts the visibility at sub-GHz frequencies, creating so-called radio phoenices. This compression can be the result of bulk motion and shocks in the ICM due to merger activity. In this paper, we demonstrate the discovery potential of low frequency radio sky surveys to find and study revived fossil plasma sources in galaxy clusters. We used the 150 MHz TGSS and 1.4 GHz NVSS sky surveys to identify candidate radio phoenices. A subset of three candidates were studied in detail using deep multi-band radio observations (LOFAR and GMRT), X-ray (Chandra or XMM-Newton) and archival optical observations. Two of the three sources are new discoveries. Using these observations, we identified common observational properties (radio morphology, ultra-steep spectrum, X-ray luminosity, dynamical state) that will enable us to identify this class of sources more easily, and helps to understand the physical origin of these sources.

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Information Architecture Automatization for the Semantic Web

Abstract: Our proposal is to develop generic Information Architecture components to facilitate publishing and browsing semantic data in the web, improving its usability and accessibility.

Cited by 35 publications

References 5 publications

A non-ideal magnetohydrodynamic gadget: simulating massive galaxy clusters

A non-ideal magnetohydrodynamic gadget: simulating massive galaxy clusters

Structure and turbulence in simulated galaxy clusters and the implications for the formation of radio haloes

Revived fossil plasma sources in galaxy clusters

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