Thermal and non-thermal traces of AGN feedback: results from cosmological AMR simulations

We investigate the observable effects of feedback from Active Galactic Nuclei (AGN) on non-thermal 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 gamma-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 gamma-ray luminosity resulting from secondary cosmic rays that is about 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.Comment: 24 pages, 20 figures. MNRAS accepted. A version of the paper with higher quality figures can be found at this url: http://www.ira.inaf.it/~vazza/papers/feedback_vazza.pd

On the amplification of magnetic fields in cosmic filaments and galaxy clusters

The amplification of primordial magnetic fields via a small-scale turbulent dynamo during structure formation might be able to explain the observed magnetic fields in galaxy clusters. The magnetisation of more tenuous large-scale structures such as cosmic filaments is more uncertain, as it is challenging for numerical simulations to achieve the required dynamical range. In this work, we present magneto-hydrodynamical cosmological simulations on large uniform grids to study the amplification of primordial seed fields in the intracluster medium (ICM) and in the warm-hot-intergalactic medium (WHIM). In the ICM, we confirm that turbulence caused by structure formation can produce a significant dynamo amplification, even if the amplification is smaller than what is reported in other papers. In the WHIM inside filaments, we do not observe significant dynamo amplification, even though we achieve Reynolds numbers of $R_{\rm e} \sim 200-300$. The maximal amplification for large filaments is of the order of $\sim 100$ for the magnetic energy, corresponding to a typical field of a few $\sim \rm nG$ starting from a primordial weak field of $10^{-10}$ G (comoving). In order to start a small-scale dynamo, we found that a minimum of $\sim 10^2$ resolution elements across the virial radius of galaxy clusters was necessary. In filaments we could not find a minimum resolution to set off a dynamo. This stems from the inefficiency of supersonic motions in the WHIM in triggering solenoidal modes and small-scale twisting of magnetic field structures. Magnetic fields this small will make it hard to detect filaments in radio observations.Comment: MNRAS accepted, in press. 18 pages, 18 Figures. New version to match with the one published in MNRAS. Updated publication list and footnote added to the title as obituary notic

Forecasts for the detection of the magnetised cosmic web from cosmological simulations

The cosmic web contains a large fraction of the total gas mass in the universe but is difficult to detect at most wavelengths. Synchrotron emission from shock-accelerated electrons may offer the chance of imaging the cosmic web at radio wavelengths. In this work we use 3D cosmological ENZO-MHD simulations (combined with a post-processing renormalisation of the magnetic field to bracket for missing physical ingredients and resolution effects) to produce models of the radio emission from the cosmic web. In post-processing we study the capabilities of 13 large radio surveys to detect this emission. We find that surveys by LOFAR, SKA1-LOW and MWA have a chance of detecting the cosmic web, provided that the magnetisation level of the tenuous medium in filaments is of the order of 1% of the thermal gas energy.Comment: 19 pages, 18 figures. A&A accepted, in press. The public repository of radio maps for the full volumes studied in this work is available at http://www.hs.uni-hamburg.de/DE/Ins/Per/Vazza/projects/Public_data.htm

Convolutional deep denoising autoencoders for radio astronomical images

We 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

Detecting shocked intergalactic gas with X-ray and radio observations

Detecting the thermal and non-thermal emission from the shocked cosmic gas surrounding large-scale structures represents a challenge for observations, as well as a unique window into the physics of the warm-hot intergalactic medium. In this work, we present synthetic radio and X-ray surveys of large cosmological simulations in order to assess the chances of jointly detecting the cosmic web in both frequency ranges. We then propose best observing strategies tailored for existing (LOFAR, MWA and XMM) or future instruments (SKA-LOW and SKA-MID, ATHENA and eROSITA). We find that the most promising targets are the extreme peripheries of galaxy clusters in an early merging stage, where the merger causes the fast compression of warm-hot gas onto the virial region. By taking advantage of a detection in the radio band, future deep X-ray observations will probe this gas in emission, and help us to study plasma conditions in the dynamic warm-hot intergalactic medium with unprecedented detail.Comment: 22 pages, 25 Figures. A\&A accepted, in press. Moderate revision compared to version 1, with a few new figure

European actions for High-Performance Computing: PRACE, DEISA and HPC-Europa

Between e-Infrastructures, ESFRI has identified in FP7 High- Performance Computing a strategic priority for Europe. In order to have the highest return from the associated massive economical and political commitment, HPC resources must be exploited at the highest level. Their access must be effective and capillary, their services must allow more and more people to use the resources, regardless their geographical location. Projects like PRACE, DEISA and HPC-Europa have been supported by the EU to cope with such issues providing the best solutions for the European research community

The turbulent pressure support in galaxy clusters revisited

Due to their late formation in cosmic history, clusters of galaxies are not fully in hydrostatic equilibrium and the gravitational pull of their mass at a given radius is expected not to be entirely balanced by the thermal gas pressure. Turbulence may supply additional pressure, and recent (X-ray and SZ) hydrostatic mass reconstructions claim a pressure support of $\sim 5-15\%$ of the total pressure at $R_{\rm 200}$. In this work we show that, after carefully disentangling bulk from small-scale turbulent motions in high-resolution simulations of galaxy clusters, we can constrain which fraction of the gas kinetic energy effectively provides pressure support in the cluster's gravitational potential. While the ubiquitous presence of radial inflows in the cluster can lead to significant bias in the estimate of the non-thermal pressure support, we report that only a part of this energy effectively acts as a source of pressure, providing a support of the order of $\sim 10\%$ of the total pressure at $R_{\rm 200}$.Comment: 5 pages, 5 pages, accepted, to appear in MNRAS Letter

Visualization, Exploration and Data Analysis of Complex Astrophysical Data

In this paper we show how advanced visualization tools can help the researcher in investigating and extracting information from data. The focus is on VisIVO, a novel open source graphics application, which blends high performance multidimensional visualization techniques and up-to-date technologies to cooperate with other applications and to access remote, distributed data archives. VisIVO supports the standards defined by the International Virtual Observatory Alliance in order to make it interoperable with VO data repositories. The paper describes the basic technical details and features of the software and it dedicates a large section to show how VisIVO can be used in several scientific cases.Comment: 32 pages, 15 figures, accepted by PAS