2,443 research outputs found
The impact of a young radio galaxy: clues from the cosmic ray electron population
No full textIn 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 ± 0.2 Myr 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
The particle content of low-power radio galaxies in groups and clusters
No full textThe 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
Spectral ageing in the lobes of FR-II radio galaxies: new methods of analysis for broad-band radio data
No full textThe broad-bandwidth capabilities of next generation telescopes such as the Jansky Very Large Array (JVLA) mean that the spectrum of any given source varies significantly within the bandwidth of any given observation. Detailed spectral analysis taking this variation into account is set to become standard practice when dealing with any new broad-band radio observations; it is therefore vital that methods are developed to handle this new type of data. In this paper, we present the Broadband Radio Astronomy ToolS (brats) software package and, use it to carry out detailed analysis of JVLA observations of three powerful radio galaxies. We compare two of the most widely used models of spectral ageing, the Kardashev–Pacholczyk and Jaffe–Perola models and also results of the more complex, but potentially more realistic, Tribble model. We find that the Tribble model provides both a good fit to observations as well as providing a physically realistic description of the source. We present the first high-resolution spectral maps of our sources and find that the best-fitting injection indices across all models take higher values than have previously been assumed. We present characteristic hotspot advance speeds and make comparison to those derived from dynamical ages, confirming the previously known discrepancy in speed remains present when determined at high spectral resolutions. We show that some previously common assumptions made in determining spectral ages with narrow-band radio telescopes may not always hold and strongly suggest that these are accounted for in future investigations
Experimental evidence for a second coordination sphere water molecule in the hydration structure of YbDTPA - Insights for a re-assessment of the relaxivity data of GdDTPA
No full textThe low temperature (-100 °C) X-ray structure of the complex K2[Yb(DTPA)(H2O)] has been determined. The metal ion is at the center of a tricapped trigonal prism and is nine-coordinate, binding to the three nitrogens and five oxygens of the ligand and one water molecule. From the structure obtained, three well-defined hydration shells can be observed consisting of: i) one coordinated water molecule; ii) several water molecules in the outer coordination sphere of the Yb(III) ion and iii) one water molecule surprisingly close to the metal center and hydrogen-bonded to proximate carboxylate groups. A variable-field and temperature NMRD study of the corresponding Gd complex has been performed and the data interpreted by taking into account the presence of second-sphere water molecule(s). The results of the analysis are in excellent agreement with the X-ray structural data
PAMAM dendrimeric conjugates with a Gd-DOTA phosphinate derivative and their adducts with polyaminoacids: The interplay of global motion, internal rotation, and fast water exchange
No full textTrinuclear copper(I)-bipyridine triskelion: Template/bascule control of coordination complex stereochemistry in a trefoil knot precursor
No full textThe construction of molecules such as knots and links can be facilitated by using metal-ligand coordination complexes as template structures; however, the control of the stereochemistry by cooperative steric interactions among metal-ligand sites remains a challenge. A simple, but general, cantilever control mechanism is demonstrated here through the stereoselective synthesis of a trinuclear copper(I)-bipyridine triskelion (see picture)
Molecular dynamics simulation of [Gd(EGTA)(H2O)]- in aqueous solution: internal motions of the poly(amino carboxylate) and water ligands, and rotational correlation times
No full textA radio through x-ray study of the jet/companion-galaxy interaction in 3C 321
No full textWe present a multiwavelength study of the nucleus, environment, jets, and hot spots of the nearby FR II radio galaxy 3C 321, using new and archival data from MERLIN, the VLA, Spitzer, HST, and Chandra. An initially collimated radio jet extends northwest from the nucleus of its host galaxy and produces a compact knot of radio emission adjacent (in projection) to a companion galaxy, after which it dramatically flares and bends, extending out in a diffuse structure 35 kpc northwest of the nucleus. We argue that the simplest explanation for the unusual morphology of the jet is that it is undergoing an interaction with the companion galaxy. Given that the northwest hot spot that lies 250 kpc from the core shows X-ray emission, which likely indicates in situ high-energy particle acceleration, we argue that the jet-companion interaction is not a steady state situation. Instead, we suggest that the jet has been disrupted on a timescale less than the light-travel time to the end of the lobe, ~106 yr, and that the jet flow to this hot spot will only be disrupted for as long as the jet-companion interaction takes place. The host galaxy of 3C 321 and the companion galaxy are in the process of merging, and each hosts a luminous AGN. As this is an unusual situation, we investigate the hypothesis that the interacting jet has driven material on to the companion galaxy, triggering its AGN. Finally, we present detailed radio and X-ray observations of both hot spots, which show that there are multiple emission sites, with spatial offsets between the radio and X-ray emission
Variability in fricative production of young people with Down's syndrome : an EPG analysis
No full textSpeech production in Down's syndrome is highly variable, with particular problems arising from complex articulations such as fricatives. In this paper, EPG analysis is used to study the variation in the production of the fricatives /s/ and /sh/ in 6 young people with Down’s syndrome. The variability of these productions is compared with information from the Robbins and Klee Oral/Speech Motor Control Protocol
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