COLLISIONAL VERSUS COLLISIONLESS MATTER: A ONE-DIMENSIONAL ANALYSIS OF GRAVITATIONAL CLUSTERING

We 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 $P(k) \propto k^n$ are assumed. We analyse the distribution of density fluctuations and thermodynamical quantities for different spectral indices $n$ and discuss the statistical properties of clustering in the corresponding simulations. At large scales the final distribution of the two components is very similar while at small scales the dark matter presents a lumpiness which is not found in the baryonic matter. The amplitude of density fluctuations in each component depends on the spectral index $n$ and only for $n=-1$ the amplitude of baryonic density fluctuations is larger than that in the dark component. This result is also confirmed by the behaviour of the bias factor, defined as the ratio between the r.m.s of baryonic and dark matter fluctuations at different scales: while for $n=1,\ 3$ it is always less than unity except at very large scales where it tends to one, for $n=-1$ it is above 1.4 at all scales. All simulations show also that there is not an exact correspondence between the positions of largest peaks in dark and baryonic components, as confirmed by a cross-correlation analysis. The final temperatures depend on the initial spectral index: the highest values are obtained for $n=-1$ and are in proximity of high density regions.Comment: 7 pages Latex (MN style) + 10 figures in postscript files, uuencoded submitted to MNRA

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

Le contexte sociopolitique du Projet de paix perpétuelle d’Emmanuel Kant

Comprendre que le contexte sociopolitique dans lequel Kant a élaboré son Projet de paix perpétuelle était marqué par l’existence d’une pluralité de formes de souveraineté permet de mieux saisir la nature de son républicanisme. En retour, cela permet de définir plus adéquatement les angles morts des catégories avec lesquelles il a pensé la modernité naissante. Après avoir mis en relief le chronofétichisme de la thèse contemporaine de la paix démocratique, l’article propose une réinterprétation du projet kantien fondée sur l’examen du contexte sociopolitique européen de la fin du 18e siècle. Il conclut en esquissant certaines pistes de réflexion pour une conceptualisation alternative de la paix démocratique qui prenne en compte le développement inégal et combiné du capitalisme au 19e siècle.To understand that the socio-political context in which Kant developed his “Perpetual Peace” was marked by the existence a plurality of forms of sovereignty and social property regimes can lead to a more rigorous understanding of the nature of his republicanism. In turn, it allows us to identify certain blind spots in Kant’s theorization of nascent modernity. After having pointed to the chrono-fetishism of contemporary democratic peace theory, this article proposes a reinterpretation of the Kantian project based on the examination of the socio- political of the late 18th century. The conclusion outlines a tentative theorization of an alternative conceptualization of the democratic peace that takes into account the uneven and combined development of capitalism during the 19th century

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

Project Hetura: Reflections on an International Local Government Partnership

The objective of this paper is to provide an overview of the Townsville/Port Moresby partnership activities and explore the challenges and benefits to both Councils from the perspective of a Townsville City Council employee associated with the program.Since 2002, Townsville City Council has been engaged in a capacity building project with the National Capital District Commission (NCDC) in Port Moresby, Papua New Guinea. The project, named Hetura, means mateship or friendship in Moto, the predominant language group in Port Moresby. Project Hetura is coordinated through the Commonwealth Local Government Forum’ (CLGF) Good Practice Scheme with funding from AusAID. Townsville City Council provides in-kind support through the contribution of staff time and participation while the National Capital District Commission provides a budget allocation for the project.The overarching goal of Project Hetura is to strengthen management, planning, and governance within the NCDC and to improve the capacity of the organisation to deliver efficient, responsive, accountable services to the community. Rather than engaging in a traditional consultancy, the approach by participants of Project Hetura has been that of a partnership built through a relationship of trust and good-will developed over time between the two organisations. Within this partnership, the skills and contributions of all parties are valued, and team members work together to develop sustainable solutions to identified problems

Properties of Cosmological Filaments extracted from Eulerian Simulations

Using a new parallel algorithm implemented within the VisIt framework, we analysed large cosmological grid simulations to study the properties of baryons in filaments. The procedure allows us to build large catalogues with up to $\sim 3 \cdot 10^4$ filaments per simulated volume and to investigate the properties of cosmic filaments for very large volumes at high resolution (up to $300^3 ~\rm Mpc^3$ simulated with $2048^3$ cells). We determined scaling relations for the mass, volume, length and temperature of filaments and compared them to those of galaxy clusters. The longest filaments have a total length of about $200 ~\rm Mpc$ with a mass of several $10^{15} M_{\odot}$. We also investigated the effects of different gas physics. Radiative cooling significantly modifies the thermal properties of the warm-hot-intergalactic medium of filaments, mainly by lowering their mean temperature via line cooling. On the other hand, powerful feedback from active galactic nuclei in surrounding halos can heat up the gas in filaments. The impact of shock-accelerated cosmic rays from diffusive shock acceleration on filaments is small and the ratio of between cosmic ray and gas pressure within filaments is of the order of $\sim 10-20$ percent.Comment: 27 pages, 24 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journa

Geopolitics, State-Formation and Economic Development in Quebec and Ontario

This dissertation challenges the prevailing periodization of Quebec and Ontario’s economic development in Canadian historiography by contrasting the specificity of capitalist social relations with the non-capitalist forms of social reproduction belonging to French Canadian peasants and Upper Canadian farmers in the colonial period. With a few notable exceptions, existing historical interpretations assume that capitalism was there, at least in embryo, from the colony’s very beginning in the guise of the fur trade, manufacturing, or a local bourgeoisie. By contrast, this thesis brings together, through a comparative perspective, different pieces of the interconnected histories of France, Britain, the United States, Ontario, and Quebec in order to show that capitalism did not arrive on the shores of the St. Lawrence River with the first settlers. The dissertation also brings together pieces of the uneven intra-regional histories of these regions, and provides a general reflection on how to systematically integrate the geopolitical dimension of social change into historical sociology, political economy, and comparative politics. As such, the question with which the thesis is concerned is not exclusively that of the transition to capitalism in Quebec or in Ontario, but more broadly the interrelated questions of state-formation and ‘late development’ in north-eastern North America. One of the main findings of the dissertation is that only with the development of industrial capitalism in the north-eastern United States were the conditions for the emergence of capital-intensive types of agriculture in rural areas of Quebec and Ontario put in place. American breakthroughs toward industrial capitalism irrevocably transformed the system-wide conditions under which subsequent agricultural evolution took place in neighbouring regions, generating a new geopolitical configuration in which customary peasant production continued to persist in Quebec alongside petty-commodity farmers in Upper Canada and the development of industrial capitalism in urban areas such as Montreal. These findings bring to the fore the need to directly address the ‘peasant question’ in order to understand the impact of the continued existence of a large peasantry on state-formation and the long-term economic development of Quebec during the period when industrial capitalism was emerging as a dominant feature of the North American economy

GPU Accelerated Particle Visualization with Splotch

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 for data transfers, computations and memory access, 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 optimized data organisation and classification of particles. We deploy a reference 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 emerging technologies.Comment: 25 pages, 9 figures. Astronomy and Computing (2014

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