Evidence for toroidal B-field components in AGN jets on kiloparsec scales

Though helical magnetic fields are generally believed to arise when the jets of Active Galactic Nuclei (AGN) are launched, it is still unclear what role they play (and if they survive) to the largest jet scales. A helical or toroidal B-field may contribute substantially to the collimation of the jet. This B-field structure can be detected in images of the Faraday rotation measure (RM)—a measure of the change in polarisation angle of an electromagnetic wave as it passes through a magneto-ionic medium. The Faraday rotation measure is directly proportional to the line-of-sight magnetic field; therefore a monotonic gradient in the RM transverse to the jet indicates similar behaviour of the line-of-sight B-field component. This type of analysis has mostly been done on parsec scales using VLBI observations at centimetre wavelengths, while relatively few studies have probed decaparsec to kiloparsec scales. The detection of RM gradients with significances of 3σ or more on such large scales can demonstrate the presence of a toroidal field component, which may be associated with a helical field that has persisted to these distances from the centre of the AGN. We present the results of new Faraday rotation analyses for 2 AGN on kiloparsec scales based on multiwavelength VLA observations, with robust transverse RM gradients detected in both. Furthermore, the direction of the inferred toroidal B-fields on the sky supports previous results indicating a predominance of outward currents in the jets on kiloparsec scales

Evolution of the magnetic field structure in the jet outflows from active galaxies

This thesis concerns studies into the magnetic fields in the jets from active galactic nuclei (AGN). Helical and toroidal magnetic fields are expected to exist in AGN jets close to the jet base and to assist in the launching and collimation of these structures, however if they can persist to the large kiloparsec scales and whether they still affect the jet on those scales is unknown. The magnetic fields of AGN jets are studied using Faraday rotation measure, which is proportional to the line of sight magnetic field strength, a transverse gradient in this value being an indicator of a toroidal magnetic field. It has been predicted by the “Cosmic Battery” model that the direction of any observed kiloparsec scale toroidal field component is such that an associated outward electrical current is present in the jet. Multiwavelength observations of 9 AGN are studied in this thesis. Of these 9 sources, 6 display significant transverse RM gradients on kiloparsec scales, of which 5 indicate toroidal fields with outward associated electrical currents, as predicted by the Cosmic Battery. Furthermore, the magnetic field environments of the jets are analysed as to how much the jets interact with their external medium. These effects can be studied using spectropolarimetry, where the behaviour of fractional polarization and polarization angle over a wide and continuous range of wavelengths can show evidence of strong depolarization and other complex magnetic field effects, some of which can be attributed to interactions with external media. An in-depth analysis of Coma A using wide band observations is presented here with accompanying Hα observations, showing regions of significant depolarization spatially correlated with observed Hα. The Hα can be used to estimate electron density, and in combination with the rotation measure values, the magnetic field can be calculated directly. It is shown that in a particular region, the depolarizing screen features a magnetic field strength upward of 36 μG, indicating the Hα gas was mixing with the radio lobe. In a similar vein, investigations into the radio galaxies 3C 382 and 3C 433 are also presented albeit without accompanying Hα data. However useful new rotation measure maps are provided for these sources, of which none have been published earlier, made using traditional χ versus λ squared fitting and rotation measure synthesis. Some of the interesting features in these sources are fitted for depolarization models to infer more complex underlying structure and were compared with previous published data at higher resolutions

Sport as an Emerging Area of Social Work Practice: New Playmakers in the Athletic Arena

Sport has been recognized as a setting for social work practice for decades, with social workers practicing in diverse sport systems, from community recreation to professional sport. However, as an emerging area of practice, little is known about these social workers. The current study aims to understand how social workers who work in sport understand their own role in this area of practice. Fifteen social workers – who had on average 12.7 years of experience and were employed in a variety of sport systems and settings – participated in individual semi-structured interviews. Thematic analysis revealed that although social workers viewed themselves as distinct from other service professionals, their sense of a professional identity was still evolving. Additionally, findings indicate that other social workers and sports professionals had a general lack of understanding about their role(s). Ultimately, there is a need to expand upon research informing formalized social work education

The magnetic field strength of the Faraday screen surrounding the radio galaxy Coma A

Studying the interaction between AGN jets and lobes and their surrounding environment is important in order to understand how they transfer energy to their environment as well as determining the intrinsic physical properties of the sources themselves. This paper presents broad-band VLA polarization and Faraday rotation observations of the radio galaxy Coma A (3C 277.3) from 1 to 4 GHz, including archival VLA observations at 4.9 and 15 GHz. Through broad-band polarization model-fitting, we find that an external Faraday screen with a turbulent magnetic field provides an appropriate description to most of the data. By combining the polarization and Faraday rotation results with previous H  α observations, we identified the H α-emitting gas as the Faraday screen responsible for the observed Faraday depolarization. We were able to derive the magnetic field strength in the H α-emitting gas, finding typical field strengths of ∼1 μG, which is consistent with studies of the intragroup medium local to other radio galaxies. However, we find a highly depolarized region of the southern lobe coincident with a H α filament that has a field strength comparable to the equipartition field strength in the radio lobe (i.e. ≳36 μG). This implies that the H α filament is internal to the radio emitting plasma. Such clear examples of internal Faraday depolarization are rare, thus providing another key insight into the evolution of radio galaxies and their ability to provide significant feedback on the local gas that would otherwise cool and form stars

Electrochemical insights into the mechanism of NiFe membrane-bound hydrogenases

Hydrogenases are enzymes of great biotechnological relevance because they catalyse the interconversion of H2, water (protons) and electricity using non-precious metal catalytic active sites. Electrochemical studies into the reactivity of NiFe membrane-bound hydrogenases (MBH) have provided a particularly detailed insight into the reactivity and mechanism of this group of enzymes. Significantly, the control centre for enabling O2 tolerance has been revealed as the electron-transfer relay of FeS clusters, rather than the NiFe bimetallic active site. The present review paper will discuss how electrochemistry results have complemented those obtained from structural and spectroscopic studies, to present a complete picture of our current understanding of NiFe MBH

daknuett/nmth: Version 0.0.1-b

<p>Adds a little more information to the readme.</p&gt

daknuett/esis: ESIS 0.0.4

<ul> <li>Improvements to <code>esis list</code>.</li> <li>Added <code>esis freeze-requirement</code></li> </ul&gt