1,721,037 research outputs found
A survey of the thermal and non-thermal properties of cosmic filaments
Full text linkIn this paper, we exploit a large suite of ENZO cosmological magneto-hydrodynamical simula- tions adopting uniform mesh resolution, to investigate the properties of cosmic filaments under different baryonic physics and magnetogenesis scenarios. We exploit a isovolume based algo- rithm to identify filaments and determine their attributes from the continuous distribution of gas mass density in the simulated volumes. The global (e.g. mass, size, mean temperature and magnetic field strength, enclosed baryon fraction) and internal (e.g. density, temperature, ve- locity and magnetic field profiles) properties of filaments in our volume are calculated across almost four orders of magnitude in mass. The inclusion of variations in non-gravitational physical processes (radiative cooling, star formation, feedback from star forming regions and active galactic nuclei) as well as in the seeding scenarios for magnetic fields (early magnetisa- tion by primordial process vs later seeding by galaxies) allows us to study both the large-scale thermodynamics and the magnetic properties of the Warm-Hot Intergalactic Medium (WHIM) with an unprecedented detail. We show how the impact of non-gravitational physics on the global thermodynamical properties of filaments is modest, with the exception of the densest gas environment surrounding galaxies in filaments. Conversely, the magnetic properties of the WHIM in filament are found to dramatically vary as different seeding scenarios are con- sidered. We study the correlation between the properties of galaxy-sized halos and their host filaments, as well as between the halos and the local WHIM in which they lie. Significant general statistical trends are reported
Multiwavelength cross-correlation analysis of the simulated cosmic web
Full text linkWe used magnetohydrodynamical cosmological simulations to investigate the cross-correlation between different observables (i.e. X-ray emission, Sunyaev-Zeldovich (SZ) signal at 21 cm, HI temperature decrement, diffuse synchrotron emission, and Faraday Rotation) as a probe of the diffuse matter distribution in the cosmic web. We adopt a uniform and simplistic approach to produce synthetic observations at various wavelengths, and we compare the detection chances of different combinations of observables correlated with each other and with the underlying galaxy distribution in the volume. With presently available surveys of galaxies and existing instruments, the best chances to detect the diffuse gas in the cosmic web outside of haloes is by cross-correlating the distribution of galaxies with SZ observations. We also find that the cross-correlation between the galaxy network and the radio emission or the Faraday Rotation can already be used to limit the amplitude of extragalactic magnetic fields, well outside of the cluster volume usually explored by existing radio observations, and to probe the origin of cosmic magnetism with the future generation of radio surveys
Numerical Cosmology: Parallel Implementations of the HYDROPAD Code
No full textWe present the parallel implementation of the HYDROPAD code, an hydrodynamical cosmosmological code for cosmological simulations which uses the Piecewise Parabolic Method (PPM) to follow the dynamics of the gas component and a Particle-Mesh N-body algorithm for the evolution of the collisionless component
Convolutional deep denoising autoencoders for radio astronomical images
Full text linkWe apply a Machine Learning technique known as Convolutional Denoising Autoencoder to denoise synthetic images of state-of-the-art radio telescopes, with the goal of detecting the faint, diffused radio sources predicted to characterize the radio cosmic web. In our application, denoising is intended to address both the reduction of random instrumental noise and the minimization of additional spurious artefacts like the sidelobes, resulting from the aperture synthesis technique. The effectiveness and the accuracy of the method are analysed for different kinds of corrupted input images, together with its computational perfoance. Specific attention has been devoted to create realistic mock observations for the training, exploiting the outcomes of cosmological numerical silations, to generate images corresponding to LOFAR HBA 8 h observations at 150 MHz. Our autoencoder can effectively denoise complex images identifying and extracting faint objects at the limits of the instrumental sensitivity. The method can efficiently scale on large data sets, exploiting high-perfoance computing solutions, in a fully automated way (i.e. no human supervision is required after training). It can accurately perfo image segmentation, identifying low brightness outskirts of diffused sources, proving to be a viable solution for detecting challenging extended objects hidden in noisy radio observations
Simulations of cosmic rays in large-scale structures: Numerical and physical effects
No full textNon-thermal (relativistic) particles are injected into the cosmos by structure formation shock waves, active galactic nuclei and stellar explosions. We present a suite of unigrid cosmological simulations (up to 20483) using a two-fluid model in the grid code ENZO. The simulations include the dynamical effects of cosmic ray (CR) protons and cover a range of theoretically motivated acceleration efficiencies. For the bulk of the cosmic volume the modelling of CR processes is rather stable with respect to resolution, provided that a minimum (cell) resolution ofÌ100 kpc h-1 is employed. However, the results for the innermost cluster regions depend on the assumptions for the baryonic physics. Inside clusters, non-radiative runs at high resolution tend to produce an energy density of CRs that are below available upper limits from the Fermi satellite, while the radiative runs are found to produce a higher budget of CRs. We show that weak (M ⤠3-5) shocks and shock-re-acceleration are crucial to set the level of CRs in the innermost region of clusters, while in the outer regions the level of CR energy is mainly set via direct injection by stronger shocks, and is less sensitive to cooling and feedback from active galactic nuclei and supernovae. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society
One-Dimensional Hydrodynamical Simulations of Gravitational Clustering in an Expanding Background
No full textThe authors present the results of a series of one-dimensional N-body and hydrodynamical simulations which have been used for testing the different clustering properties of baryonic and dark matter in an expanding background. Initial Gaussian random density perturbations with a power-law spectrum are assumed. They analyse the distribution of density fluctuations and thermodynamical quantities for different spectral indices and discuss the statistical properties of clustering in the corresponding simulations
A Cosmological Hydrodynamic code based on the Piecewise Parabolic Method
No full textWe present a hydrodynamical code for cosmological simulations which uses the piecewise parabolic method (PPM) to follow the dynamics of the gas component and an N-body particle-mesh algorithm for the evolution of the collisionless component. The gravitational interaction between the two components is regulated by the Poisson equation, which is solved by a standard fast Fourier transform (FFT) procedure. In order to simulate cosmological flows, we have introduced several modifications to the original PPM scheme, which we describe in detail. Various tests of the code are presented, including adiabatic expansion, single and multiple pancake formation, and three-dimensional cosmological simulations with initial conditions based on the cold dark matter scenario
Thermal and non-thermal traces of agn feedback: Results from cosmological amr simulations
No full textWe investigate the observable effects of feedback from active galactic nuclei (AGN) on nonthermal components of the intracluster medium (ICM). We have modelled feedback from AGN in cosmological simulations with the adaptive mesh refinement code ENZO, investigating three types of feedback that are sometimes called quasar, jet and radio mode. Using a small set of galaxy clusters simulated at high resolution, we model the injection and evolution of cosmic rays, as well as their effects on the thermal plasma. By comparing both the profiles of thermal gas to observed profiles from the ACCEPT sample and the secondary Î3 -ray emission to the available upper limits from Fermi, we discuss how the combined analysis of these two observables can constrain the energetics and mechanisms of feedback models in clusters. Those modes of AGN feedback that provide a good match to X-ray observations yield a Î3 -ray luminosity resulting from secondary cosmic rays that is about 10 times below the available upper limits from Fermi. Moreover, we investigate the injection of turbulent motions into the ICM from AGN, and the detectability of these motions via the analysis of line broadening of the Fe XXIII line. In the near future, deeper observations/upper limits of non-thermal emissions from galaxy clusters will yield stringent constraints on the energetics and modes of AGN feedback, even at early cosmic epochs. © 2012 The Authors
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