401 research outputs found
Advanced oxidation and adsorption technologies for organic micropollutant removal from lake water used as drinking-water supply
No full text
Potential genotoxic effects of surface drinking water treated with chlorine and alternative disinfectans
No full textA new sample of large angular size radio galaxies. III Statistics and evolution of the grown population
No full textParticle acceleration in cooling flow clusters of galaxies: The case of Abell 2626
No full textRecently a theoretical model has been proposed that accounts for the origin of radio mini-halos observed in some cooling flow clusters as related to electron re-acceleration by MHD turbulence (Gitti et al. [CITE]). The MHD turbulence is assumed to be frozen into the flow of the thermal ICM and thus amplified in the cooling flow region. Here we present the application of this model to a new mini-halo candidate, the cluster A2626, and compare the results with those obtained for the mini-halo in the Perseus cluster. We present VLA data at 330 MHz and 1.5 GHz of the diffuse radio emission observed in A2626, and we show that its main properties can be explained by the model. We find that the power necessary for the re-acceleration of the relic electron population is only a factor of ~0.7% of the maximum power that can be extracted from the cooling flow (as estimated on the basis of the standard model). We also discuss the observational properties of known mini-halos in connection with those of host clusters, showing that the radio power of mini-halos increases with the maximum power of cooling flows. This trend is expected in the framework of the model. Possible effects of new Chandra and XMM-Newton estimates of on this trend are considered: we conclude that even if earlier derived cooling rates were overestimated, cooling flow powers are still well above the radio powers emitted by mini-halo
The diffuse radio filament in the merging system ZwCl 2341.1+0000
No full textContext. In some clusters of galaxies, a diffuse non-thermal emission is
present, not obviously associated with any individual galaxy. These sources
have been identified as relics, mini-halos, and halos according to their
properties and position with respect to the cluster center. In a few
cases diffuse radio emission has been reported that cannot be
identified with a cluster, but with a large scale filamentary region.
Aims. We observe and analyze the diffuse radio emission
present in the complex merging structure of galaxies ZwCl 2341.1+0000.
Methods. We obtained VLA observations at 1.4 GHz to derive a deep radio image
of the diffuse emission.
Results. Low resolution VLA images detect diffuse radio emission associated with the
complex merging region
of size =2.2 Mpc at most. In addition to the previously reported
peripheral radio emission, classified as a double relic,
diffuse emission is detected along the optical filament of
galaxies.
Conclusions. The giant radio source discussed here shows that magnetic fields and
relativistic particles are also present in filamentary structures.
Possible alternate scenarios are: a giant radio halo in-between two
symmetric relics, or the merging of two clusters both hosting a central
radio halo
Multifrequency VLA radio observations of the X-ray cavity cluster of galaxies RBS797: evidence of differently oriented jets
No full textWe report on the peculiar activity of the radio source located at the center of the cooling flow cluster RBS 797 (z=0.35), the first distant cluster in which two pronounced X-ray cavities have been discovered. Our new multifrequency (1.4, 4.8, and 8.4 GHz) observations obtained with the Very Large Array clearly reveal the presence of radio emission on three different scales showing orientation in different directions, all of which indicates that RBS797 represents a very peculiar case. The lowest resolution images show large-scale radio emission characterized by amorphous morphology and a steep spectrum, extended on a scale of hundreds of kpc. On a scale of tens of kpc, there is evidence of 1.4 GHz radio emission elongated in the northeast-southwest direction exactly towards the holes detected in X-rays. The highest resolution image shows the details of the innermost 4.8 GHz radio jets on a kpc scale; they are remarkably oriented in a direction that is perpendicular to that of the extended structure detected at a lower resolution. We therefore find evidence of a strong interaction between the central radio source and the intra-cluster medium in RBS797. We suggest a scenario in which the 1.4 GHz emission filling the X-ray cavities consists of buoyant bubbles of radio emitting plasma that are created by twin jets in the past and whose expansion has displaced the thermal gas that was formerly in the X-ray holes, whereas the two jets visible at 4.8 GHz are related to the present nuclear activity that has restarted at a different position angle from the original outburst that created the outer radio lobes. The total radio luminosity is 10^42 erg s^-1, corresponding to a factor of a few thousand times less than the estimated cooling luminosity
Clusters of galaxies: observational properties of the diffuse radio emission
No full textClusters of galaxies, as the largest virialized systems in the Universe, are ideal laboratories to study the formation and evolution of cosmic structures. The luminous matter of clusters consists of galaxies and of an embedding intracluster medium (ICM), which has been heated to temperatures of tens of millions degrees, and thus is detected through its thermal emission in the soft X-ray regime. Most of the detailed knowledge of galaxy clusters has been obtained in recent years from the study of ICM through X-ray Astronomy. At the same time, radio observations have proved that the ICM is mixed with non-thermal components, i.e. highly relativistic particles and large-scale magnetic fields, detected through their synchrotron emission. The knowledge of the properties of these non-thermal ICM components has increased significantly, owing to sensitive radio images and to the development of theoretical models. Diffuse synchrotron radio emission in the central and peripheral cluster regions has been found in many clusters. Moreover large-scale magnetic fields appear to be present in all galaxy clusters, as derived from Rotation Measure (RM) studies. Non-thermal components are linked to the cluster X-ray properties, and to the cluster evolutionary stage, and are crucial for a comprehensive physical description of the intracluster medium. They play an important role in the cluster formation and evolution. We review here the observational properties of diffuse non-thermal sources detected in galaxy clusters: halos, relics and mini-halos. We discuss their classification and properties. We report published results up to date and obtain and discuss statistical properties. We present the properties of large-scale magnetic fields in clusters and in even larger structures: filaments connecting galaxy clusters. We summarize the current models of the origin of these cluster components, and outline the improvements that are expected in this area from future developments thanks to the new generation of radio telescopes
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