Radio galaxies and magnetic fields in A514

A514 contains six extended and polarized radio sources located at various projected distances from the cluster center. Here we present a detailed study of these six radio sources in total intensity and polarization using the Very Large Array at 3.6 and 6 cm. Since the radio sources sample different lines of sight across the cluster, an analysis of the Faraday Rotation Measures (RMs) provides information on the strength and the structure of the cluster magnetic field. These sources show a decreasing Faraday Rotation Measure with increasing distance from the cluster center. We estimate the strength of the magnetic field to be ~3-7 uG in the cluster center. From the RM structure across the stronger and more extended sources we estimate the coherence length of the magnetic field to be about 9 kpc at the cluster center.Comment: 16 pages, 18 ps figures accepted by A&

MRC B0319-454: Probing the large-scale structure with a giant radio galaxy

We present an investigation of the relationships between the radio properties of a giant radio galaxy MRC B0319-454 and the surrounding galaxy distribution with the aim of examining the influence of intergalactic gas and gravity associated with the large-scale structure on the evolution in the radio morphology. Our new radio continuum observations of the radio source, with high surface brightness sensitivity, images the asymmetries in the megaparsec-scale radio structure in total intensity and polarization. We compare these with the 3-D galaxy distribution derived from galaxy redshift surveys. Galaxy density gradients are observed along and perpendicular to the radio axis: the large-scale structure is consistent with a model wherein the galaxies trace the ambient intergalactic gas and the evolution of the radio structures are ram-pressure limited by this associated gas. Additionally, we have modeled the off-axis evolution of the south-west radio lobe as deflection of a buoyant jet backflow by a transverse gravitational field: the model is plausible if entrainment is small. The case study presented here is a demonstration that giant radio galaxies may be useful probes of the warm-hot intergalactic medium believed to be associated with moderately over dense galaxy distributions.Comment: 27 pages, 15 figures, accepted for publication in MNRA

Parsec-scale Properties of Brightest Cluster Galaxies

We present new VLBI observations at 5 GHz of a complete sample of Brightest Cluster Galaxies (BCGs) in nearby Abell Clusters (distance class <3). Combined with data from the literature, this provides parsec-scale information for 34 BCGs. Our analysis of their parsec scale radio emission and cluster X-ray properties shows a possible dichotomy between BCGs in cool core clusters and those in non cool core clusters. Among resolved sources, those in cool core clusters tend to have two-sided parsec-scale jets, while those in less relaxed clusters have predominantly one-sided parsec-scale jets. We suggest that this difference could be the result of interplay between the jets and the surrounding medium. The one-sided structure in non cool core clusters could be due to Doppler boosting effects in relativistic, intrinsically symmetric jets; two-sided morphology in cool core clusters is likely related to the presence of heavy and mildly relativistic jets slowed down on the parsec-scale. Evidence of recurrent activity are also found in BCGs in cool core clusters.Comment: 20 pages, 10 figures, accepted for publication in A&

Radio and X-ray diffuse emission in six clusters of galaxies

Deep Very Large Array radio observations confirm the presence of halo and relic sources in six clusters of galaxies (A115, A520, A773, A1664, A2254, A2744) where a wide diffuse emission was previously found in the NRAO VLA Sky Survey. New images at 1.4 GHz of these six clusters of galaxies are presented and X-ray data obtained from the ROSAT archive are analyzed. The properties of clusters hosting radio halos and relics are analyzed and discussed. A correlation between the halo radio power and the cluster gravitational mass is presented.Comment: 18 pages, 18 ps figures, accepted by A&

Hard X-ray and radio observations of Abell 754

We present a long BeppoSAX observation of Abell 754 that reports a nonthermal excess with respect to the thermal emission at energies greater than ~45 keV. A VLA radio observation at 1.4 GHz definitely confirms the existence of diffuse radio emission in the central region of the cluster, previously suggested by images at 74 and 330 MHz (Kassim et al 2001), and reports additional features. Besides, our observation determines a steeper radio halo spectrum in the 330-1400 MHz frequency range with respect to the spectrum detected at lower frequencies, indicating the presence of a spectral cutoff. The presence of a radio halo in A754, considered the prototype of a merging cluster, reinforces the link between formation of Mpc-scale radio regions and very recent or current merger processes. The radio results combined with the hard X-ray excess detected by BeppoSAX give information on the origin of the electron population responsible for nonthermal phenomena in galaxy clusters. We discuss also the possibility that 26W20, a tailed radio galaxy with BL Lac characteristics located in the field of view of the PDS, could be responsible for the observed nonthermal hard X-ray emission.Comment: 7 pages, 3 figures; Astronomy & Astrophysics, in pres

Moving from a continuum to a community: reconceptualising the provision of support

The notion of the continuum is applied to special education in diverse contexts across many nations. This paper explores its conceptual underpinnings, drawing upon a systematic search of the literature to review recurring ideas associated with the notion and to explicate both its uses and short-comings. Through a thematic analysis of the literature the research team derived twenty-nine continua, situated within six broad groupings (space, students, staffing, support, strategies and systems). This provides a clear structure for reconsidering the issues which the notion of the continuum is supposed to describe and enables a reconceptualisation of how the delivery of services is represented. We present the initial underpinnings for a community of provision, in which settings and services work together to provide learning and support for all children and young people in their locality

Real-time two-photon confocal microscopy using a femtosecond, amplified Ti:sapphire system

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71623/1/j.1365-2818.1996.97379.x.pd