The particle content of low-power radio galaxies in groups and clusters

The synchrotron-radiating particles and magnetic fields in low-power radio galaxies (including most nearby cluster-centre sources), if at equipartition, can provide only a small fraction of the total internal energy density of the radio lobes or plumes, which is now well constrained via X-ray observations of their external environments. We consider the constraints on models for the dominant energy contribution in low-power radio-galaxy lobes obtained from a detailed comparison of how the internal equipartition pressure and external pressure measured from X-ray observations evolve with distance for two radio galaxies, 3C 31 and Hydra A. We rule out relativistic lepton dominance of the radio lobes, and conclude that models in which magnetic field or relativistic protons/ions carried up the jet dominate lobe energetics are unlikely. Finally, we argue that entrainment of material from the jet surroundings can provide the necessary pressure, and construct a simple self-consistent model of the evolution of the entrainment rate required for pressure balance along the 100-kpc-scale plumes of 3C 31. Such a model requires that the entrained material is heated to temperatures substantially above that of the surrounding intragroup medium, and that the temperature of the thermal component of the jet increases with distance, though remaining sub-relativistic.Peer reviewe

FRII sources at z>0.5: X-ray properties of the core and extended emission

Peer reviewe

Rejuvenated radio galaxies J0041+3224 and J1835+6204 : how long can the quiescent phase of nuclear activity last?

We present radio observations of two well-known doubledouble radio galaxies, J0041+3224 and J1835+6204, at frequencies ranging from 150 to 8460 MHz, using both the Giant Metrewave Radio Telescope and the Very Large Array. These observations, over a large radio frequency range, enable us to determine the spectra of the inner and outer lobes. Our detailed spectral ageing analysis of their inner and outer lobes demonstrates that the outer doubles of doubledouble radio galaxies are created by the previous cycle of activity, while the inner doubles are due to the present cycle of activity. The (core subtracted) spectra of the inner doubles of both sources are power laws over a large frequency range. We found that the duration of the quiescent phase of J0041+3224 is between 4 and 28 per cent of the active phase of the previous activity. The outer north-western lobe of J1835+6204 has a compact hotspot and the regions of both the outer hotspots have close to power-law (rather than curved) spectra, which indicates that the outer lobes are still fed by jet material ejected in the previous episode just before the central engine stopped powering the jet. We estimate that the duration of the quiescent phase of J1835+6204 is ?5 per cent of the duration of the active phase of the previous activity. Therefore, we conclude that the duration of the quiescent phase can be as short as a few per cent of the active phase in radio galaxies of this type.Peer reviewe

Inverse-Compton emission from the lobes of 3C 353

‘The definitive version is available at www.blackwell-synergy.com.’ Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2008.13028.xX-ray emission due to inverse-Compton scattering of microwave background photons by electrons in the lobes of powerful radio galaxies has now been seen in a large number of objects. Combining an inverse-Compton model for the lobe X-ray emission with information obtained from radio synchrotron emission provides a method of constraining the electron population and magnetic field energy density, which cannot be accomplished using the radio data alone. Using six frequencies of new and archival radio data and new XMM-Newton observations of the Fanaroff & Riley class II radio galaxy 3C353, we show that inverse-Compton emission is detected in the radio lobes of this source at a level consistent with what is seen in other objects. We argue that variations in the X-ray/radio ratio in the brighter eastern lobe require positionally varying magnetic field strength. We also examine the X-ray nucleus and the cluster, Zw1819.1-0108, spatially and spectrally.Peer reviewe

The construction and experience of ability in physical education

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This thesis explores how notions of ability are socially constructed, defined and experienced within physical education (PE). Pierre Bourdieu’s concepts are used to examine the processes through an acknowledgement and consideration of the culture where pupils’ and teachers’ notions of ability are configured, reconfigured, and experienced. The study covered one academic school year in a North London mixed comprehensive school. Fifteen pupils participated in focus groups and individual interviews. The pupils were a mixture of boys (11) and girls (4), a range of abilities and ages (11 – 16 years old), and experienced PE predominantly in ability groups. In addition, six PE teachers were interviewed and PE lesson observations were conducted throughout the study. The findings identify various processes and interactions between individuals and also between individuals and the field that contribute towards the social construction of ability in PE. The findings highlight the complex and dynamic nature of the PE experience where notions of ability and the related practices have a bearing. Hierarchical ability-based practices were apparent that served to reinforce dominant notions of ability but there were other practices that could potentially challenge ‘legitimate’ notions of ability. The study highlights some of the constraints that teachers face in their attempts to integrate broader notions of ability, especially within a performative culture. Variations across the individual experience highlight considerations for pupils in terms of becoming physically literate and reaching their potential. The study aims to raise key questions for stakeholders in considering how ability-based practices work in facilitating a learning environment that supports all levels of ability and preparing all young people for lifelong activity. In addition it stresses the need for greater agreement amongst stakeholders on the purpose of PE in the current climate and suggests that a review of the aims of PE is warranted

The Chairman or the Board? Appointments at Multimember Agencies

For the past 130 years, Congress has alternated between two competing structural visions of ideal administrative agency design—single-administrator versus multimember organization. Over time, Congress has frequently reacted to strong arguments from both sides by approving various arrangements that conflate the two models, particularly with respect to the important but often overlooked authority to appoint “inferior Officers” within multimember agencies. In many cases, the chairmen—or their equivalent—of these multimember boards and commissions retain some or all power to select high-ranking agency staff, whereas their fellow board or commission members have authority over agency rulemaking, adjudication, and other key functions. Although such power-sharing arrangements may have kept the peace in some sense for many years, recent events call into question the constitutional integrity of these mixed-management models

The impact of a young radio galaxy : Clues from the cosmic ray electron population

In the framework of hierarchical structure formation, active galactic nuclei (AGN) feedback shapes the galaxy luminosity function. Low luminosity, galaxy-scale double radio sources are ideal targets to investigate the interplay between AGN feedback and star formation. We use Very Large Array and BIMA millimetre-wave array observations to study the radio continuum emission of NGC 3801 between 1.4 and 112.4 GHz. We find a prominent spectral break at 10 GHz, where the spectrum steepens as expected from cosmic ray electron (CRe) ageing. Using the equipartition magnetic field and fitting JP models locally, we create a spatially resolved map of the spectral age of the CRe population. The spectral age of τint =2.0±0.2Myr agrees within a factor of 2 with the dynamical age of the expanding X-ray emitting shells. The spectral age varies only little across the lobes, requiring an effective mixing process of the CRe such as a convective backflow of magnetized plasma. The jet termination points have a slightly younger CRe spectral age, hinting at in situ CRe re-acceleration. Our findings support the scenario where the supersonically expanding radio lobes heat the interstellar medium (ISM) of NGC 3801 via shock waves, and, as their energy is comparable to the energy of the ISM, are clearly able to influence the galaxy's further evolution.Peer reviewe