Can giant radio halos probe the merging rate of galaxy clusters?

Radio and X-ray observations of galaxy clusters probe a direct link between cluster mergers and giant radio halos (RH), suggesting that these sources can be used as probes of the cluster merging rate with cosmic time. In this paper we carry out an explorative study that combines the observed fractions of merging clusters (fm) and RH (fRH) with the merging rate predicted by cosmological simulations and attempt to infer constraints on merger properties of clusters that appear disturbed in X-rays and of clusters with RH. We use morphological parameters to identify merging systems and analyze the currently largest sample of clusters with radio and X-ray data (M500>6d14 Msun, and 0.2<z<0.33, from the Planck SZ cluster catalogue). We found that in this sample fm~62-67% while fRH~44-51%. The comparison of the theoretical f_m with the observed one allows to constrain the combination (xi_m,tau_m), where xi_m and tau_m are the minimum merger mass ratio and the timescale of merger-induced disturbance. Assuming tau_m~ 2-3 Gyr, as constrained by simulations, we find that the observed f_m matches the theoretical one for xi_m~0.1-0.18. This is consistent with optical and near-IR observations of clusters in the sample (xi_m~0.14-0.16). The fact that RH are found only in a fraction of merging clusters may suggest that merger events generating RH are characterized by larger mass ratio; this seems supported by optical/near-IR observations of RH clusters in the sample (xi_min~0.2-0.25). Alternatively, RH may be generated in all mergers but their lifetime is shorter than \tau_m (by ~ fRH/fm). This is an explorative study, however it suggests that follow up studies using the forthcoming radio surveys and adequate numerical simulations have the potential to derive quantitative constraints on the link between cluster merging rate and RH at different cosmic epochs and for different cluster masses.Comment: 10 pages, 3 figures, accepted for publication in A&

A Novel Broadband Measurement Method for the Magnetoimpedance of Ribbons and Thin Films

A novel broad-band measurement method of the MI in thin films and ribbons is presented. It is based on the automated measurement of the reflection coefficient of a cell loaded with the sample. Illustrative results obtained with a permalloy multilayer thin film are presented and discussed.Comment: Paper submitted to International Conference on Magnetism (Rome 2003

SUSTAINABILITY OF POULTRY PRODUCTION USING THE EMERGY APPROACH: COMPARISON OF CONVENTIONAL AND ORGANIC REARING SYSTEMS

The organic production system is an important strategy, compatible with sustainable agriculture, avoiding the use of chemical compounds,limiting the intensity of production and providing controls along the entire chain of production. The aim of this study is to compare conventional and organic poultry production in terms of emergy analysis. The main differences in the two systems were the emergy cost for poultry feed and for cleaning/sanitization of the buildings between successive productive cycles. In both production systems the poultry feed represented more than 50% of the emergy flow. Regarding the agronomic phase, it was shown that almost all the organic crops, avoiding chemical fertilizers and pesticides, saved around 60% emergy. The emergetic costs for housing of the birds were very similar in both systems. Relating the emergy results with productive performance it is possible to show that, although the annual productive performance was much lower in organic than in conventional (206%), transformity of organic poultry was around 10% lower. Comparison of the organic poultry system with a conventional one from the viewpoint of sustainability showed that all the emergy-based indicators are in favour of the organic farming system with a higher efficiency in transforming the available inputs in the final product, a higher level of renewable inputs, a higher level of local inputs and a lower density of energy and matter flows

The mystery of the 'Kite' radio source in Abell 2626: insights from new Chandra observations

We present the results of a new Chandra study of the galaxy cluster A2626. The radio emission of the cluster shows a complex system of four symmetric arcs without known correlations with the X-ray emission. The mirror symmetry of the radio arcs toward the center and the presence of two optical cores in the central galaxy suggested that they may be created by pairs of precessing radio jets powered by dual AGNs inside the cD galaxy. However, previous observations failed to observe the second jetted AGN and the spectral trend due to radiative age along the radio arcs, thus challenging this interpretation. The new Chandra observation had several scientific objectives, including the search for the second AGN that would support the jet precession model. We focus here on the detailed study of the local properties of the thermal and non-thermal emission in the proximity of the radio arcs, in order to get more insights into their origin. We performed a standard data reduction of the Chandra dataset deriving the radial profiles of temperature, density, pressure and cooling time of the intra-cluster medium. We further analyzed the 2D distribution of the gas temperature, discovering that the south-western junction of the radio arcs surrounds the cool core of the cluster. We studied the X-ray SB and spectral profiles across the junction, finding a cold front spatially coincident with the radio arcs. This may suggest a connection between the sloshing of the thermal gas and the nature of the radio filaments, raising new scenarios for their origin. A possibility is that the radio arcs trace the projection of a complex surface connecting the sites where electrons are most efficiently reaccelerated by the turbulence that is generated by the gas sloshing. In this case, diffuse emission embedded by the arcs and with extremely steep spectrum should be most visible at very low radio frequencies.Comment: 7 pages, 7 figures. Accepted for publication on A&

Radio Lobes of Pictor A: an X-ray spatially resolved Study

A new XMM observation has made possible a detailed study of both lobes of the radio galaxy Pictor A. Their X-ray emission is of non thermal origin and due to Inverse Compton scattering of the microwave background photons by relativistic electrons in the lobes, as previously found. In both lobes, the equipartition magnetic field (Beq) is bigger than the Inverse Compton value (Bic), calculated from the radio and X-ray flux ratio. The Beq/Bic ratio never gets below 2, in spite of the large number of reasonable assumptions tested to calculate Beq, suggesting a lobe energetic dominated by particles. The X-ray data quality is good enough to allow a spatially resolved analysis. Our study shows that Bic varies through the lobes. It appears to increase behind the hot spots. On the contrary, a rather uniform distribution of the particles is observed. As a consequence, the radio flux density variation along the lobes appears to be mainly driven by magnetic field changes.Comment: 15 pages, 3 figures, ApJ accepte

Optical Stark Effect and Dressed Excitonic States in a Mn-doped Quantum Dot

We report on the observation of spin dependent optically dressed states and optical Stark effect on an individual Mn spin in a semiconductor quantum dot. The vacuum-to-exciton or the exciton-to-biexciton transitions in a Mn-doped quantum dot are optically dressed by a strong laser field and the resulting spectral signature is measured in photoluminescence. We demonstrate that the energy of any spin state of a Mn atom can be independently tuned using the optical Stark effect induced by a control laser. High resolution spectroscopy reveals a power, polarization and detuning dependent Autler-Townes splitting of each optical transition of the Mn-doped quantum dot. This experiment demonstrates a complete optical resonant control of the exciton-Mn system

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

The Population ageing in Italy: facts and impact on household portfolios

This paper aims to assess the impact of ageing on household portfolios in Italy and hence ultimately on financial markets. To this end, the analysis is carried out in two steps. First, the dimension of population ageing in Italy is assessed by means of both historical and forecast data on the structure of Italian population. Second, based on data taken from the Bank of Italy Survey of Household Income and Wealth (SHIW) over the last decade, we analyse the average household portfolio in relation to demographic characteristics. The main findings are: first, Italy turns out to be one of the countries most affected by ageing; second, financial choices of Italian households are sensibly affected by age. Thus, the exceptional ageing in Italy might have relevant consequences on the Italian financial market