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  • 1
    Electronic Resource
    Electronic Resource
    Modelling of leachates from dolomitic mine tailings (1987)
    Springer
    Environmental geochemistry and health 9 (1987), S. 17-22 
    Details
    ISSN: 1573-2983
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Medicine
    Notes: Abstract The REDEQL.EPAK computer model was used to study speciation of Pb, Cd, Zn, and Ca in leachates from dolomitic Pb mine tailings. By allowing or disallowing precipitation of solids and equilibration of the modelled leachate with atmospheric C02, comparison of fresh and aged leachates was made. The effects of treatment of the tailings with phosphate containing fertilizer were studied through addition of P04 3− to the modelled solution. Equilibrium constants pertaining to metal ion-humic acid complexation were added to the thermodynamic data base of the model in order to study the effects of decaying plant material on tailings leachate. Initial leachate of the tailings is found to be supersaturated with Cd and Zn. Non-complexed (“free”) Cd2+ and Zn2+ is predicted to comprise most of the soluble form of these metals in the leachate; Pb is predicted to be present largely as PbCO3 ion pair. Equilibration of the leachate with the atmosphere is predicted to lead to extensive precipitation of CdCO3 and ZnSiO3. Precipitation of Pb5(PO4)3Cl is predicted at high PO4 3− concentration and at low pH. Complexation by the humic acid is predicted to compete effectively with other ligands in the leachate for the metal ions. The results are compared with experimental findings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01811112
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of cover materials on leaching of constituents from dolomitic lead mine tailings (1987)
    Springer
    Water, air & soil pollution 34 (1987), S. 31-43 
    Details
    ISSN: 1573-2932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Five raised-bed test plots were used to study the effects of cover materials on the leaching of constituents from dolomitic Pb mine tailings over a 2-yr period. The cover materials studied were a fertilizer and seed mixture, anaerobically digested sewage sludge, loam and sod, and fallen leaves from silver maples (Acer Saccharinum); one plot was not covered. Fresh leachates and receiving pool waters were analyzed for ten metals, Si, P, inorganic anions, filterable organic carbon (FOC), and alkalinity. The mixture of fertilizer and seed decreased leaching of Pb and Zn during the first year. The leaf cover increased leaching of Pb during both years; this effect decreased as the leaves weathered. Sludge caused some increase in Pb leaching during the first year, and increased Cd leaching during both years. Concentrations of most leachate constituents decreased, and pH increased in the receiving pools. Concentrations of Pb remained higher in the receiving pool for the leaf-covered plot than in the other pools. Increases in leaching of Pb and Cd with a sludge cover were moderate, and the ability of the material to support plant growth on the tailings suggested that it may be a good medium for inducing growth of vegetative cover on the dolomitic tailings. Other organic materials may cause pronounced increase in the concentration of toxic trace metals in leachate from the tailings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00176865
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  • 3
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    The widest frequency radio relic spectra: observations from 150 MHz to 30 GHz (2015)
    Oxford University Press
    Details
    Publication Date: 2015-11-25
    Description: Radio relics are patches of diffuse synchrotron radio emission that trace shock waves. Relics are thought to form when intracluster medium electrons are accelerated by cluster merger-induced shock waves through the diffusive shock acceleration mechanism. In this paper, we present observations spanning 150 MHz to 30 GHz of the ‘Sausage’ and ‘Toothbrush’ relics from the Giant Metrewave and Westerbork telescopes, the Karl G. Jansky Very Large Array, the Effelsberg telescope, the Arcminute Microkelvin Imager and Combined Array for Research in Millimeter-wave Astronomy. We detect both relics at 30 GHz, where the previous highest frequency detection was at 16 GHz. The integrated radio spectra of both sources clearly steepen above 2 GHz, at the 6 significance level, supporting the spectral steepening previously found in the ‘Sausage’ and the Abell 2256 relic. Our results challenge the widely adopted simple formation mechanism of radio relics and suggest more complicated models have to be developed that, for example, involve re-acceleration of aged seed electrons.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Spectral ageing in the lobes of cluster-centre FR II radio galaxies (2015)
    Oxford University Press
    Details
    Publication Date: 2015-10-22
    Description: Recent investigations have shown that many parameters and assumptions made in the application of spectral-ageing models to FR II radio galaxies (e.g. injection index, uniform magnetic field, non-negligible cross-lobe age variations) may not be as reliable as previously thought. In this paper we use new Very Large Array observations, which allow spectral curvature at GHz frequencies to be determined in much greater detail than has previously been possible, to investigate two cluster-centre radio galaxies, 3C 438 and 3C 28. We find that for both sources the injection index is much steeper than the values traditionally assumed, consistent with our previous findings. We suggest that the Tribble model of spectral ageing provides the most convincing description when both goodness-of-fit and physically plausibility are considered, but show that even with greatly improved coverage at GHz frequencies, a disparity exists in cluster-centre FR IIs when spectral ages are compared to those determined from a dynamical viewpoint. We find for 3C 438 that although the observations indicate the lobes are expanding, its energetics suggest that the radiating particles and magnetic field at equipartition cannot provide the necessary pressure to support the lobes, similar to other cluster-centre source such as Cygnus A. We confirm that small-scale, cross-lobe age variations are likely to be common in FR II sources and should be properly accounted for when undertaking spectral-ageing studies. Contrary to the assumption of some previous studies, we also show that 3C 28 is an FR II (rather than FR I) source, and suggest that it is most likely a relic system with the central engine being turned off between 6 and 9 Myr ago.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Spectral ageing in the lobes of FR-II radio galaxies: new methods of analysis for broad-band radio data (2013)
    Oxford University Press
    Details
    Publication Date: 2013-10-12
    Description: The 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.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Spectral age modelling of the 'Sausage' cluster radio relic (2014)
    Oxford University Press
    Details
    Publication Date: 2014-10-10
    Description: CIZA J2242.8+5301 is a post-core passage, binary merging cluster that hosts a large, thin, arc-like radio relic, nicknamed the ‘Sausage’, tracing a relatively strong shock front. We perform spatially resolved spectral fitting to the available radio data for this radio relic, using a variety of spectral ageing models, with the aim of finding a consistent set of parameters for the shock and radio plasma. We determine an injection index of $0.77^{+0.03}_{-0.02}$ for the relic plasma, significantly steeper than was found before. Standard particle acceleration at the shock front implies a Mach number $M=2.90^{+0.10}_{-0.13}$ , which now matches X-ray measurements. The shock advance speed is v shock   2500 km s –1 , which places the core passage of the two subclusters 0.6–0.8 Gyr ago. We find a systematic spectral age increase from 0 at the northern side of the relic up to ~60 Myr at ~145 kpc into the downstream area, assuming a 0.6 nT magnetic field. Under the assumption of freely ageing electrons after acceleration by the ‘Sausage’ shock, the spectral ages are hard to reconcile with the shock speed derived from X-ray and radio observations. Re-acceleration or unusually efficient transport of particle in the downstream area and line-of-sight mixing could help explain the systematically low spectral ages.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    The non-thermal superbubble in IC 10: the generation of cosmic ray electrons caught in the act (2014)
    Oxford University Press
    Details
    Publication Date: 2014-11-24
    Description: Superbubbles are crucial for stellar feedback, with supposedly high (of the order of 10 per cent) thermalization rates. We combined multiband radio continuum observations from the Very Large Array (VLA) with Effelsberg data to study the non-thermal superbubble (NSB) in IC 10, a starburst dwarf irregular galaxy in the Local Group. Thermal emission was subtracted using a combination of Balmer Hα and VLA 32 GHz continuum maps. The bubble's non-thermal spectrum between 1.5 and 8.8 GHz displays curvature and can be well fitted with a standard model of an ageing cosmic ray electron population. With a derived equipartition magnetic field strength of 44 ± 8 μG, and measuring the radiation energy density from Spitzer MIPS maps as 5 ± 1 10 –11 erg cm –3 , we determine, based on the spectral curvature, a spectral age of the bubble of 1.0 ± 0.3 Myr. Analysis of the LITTLE THINGS H  i data cube shows an expanding H  i hole with 100 pc diameter and a dynamical age 3.8 ± 0.3 Myr, centred to within 16 pc on IC 10 X-1, a massive stellar mass black hole ( M 〉 23 M ). The results are consistent with the expected evolution for a superbubble with a few massive stars, where a very energetic event like a Type Ic supernova/hypernova has taken place about 1 Myr ago. We discuss alternatives to this interpretation.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    The highest frequency detection of a radio relic: 16 GHz AMI observations of the 'Sausage' cluster (2014)
    Oxford University Press
    Details
    Publication Date: 2014-05-03
    Description: We observed the cluster CIZA J2242.8+5301 with the Arcminute Microkelvin Imager at 16 GHz and present the first high radio-frequency detection of diffuse, non-thermal cluster emission. This cluster hosts a variety of bright, extended, steep-spectrum synchrotron-emitting radio sources, associated with the intracluster medium, called radio relics. Most notably, the northern, Mpc-wide, narrow relic provides strong evidence for diffusive shock acceleration in clusters. We detect a puzzling, flat-spectrum, diffuse extension of the southern relic, which is not visible in the lower radio-frequency maps. The northern radio relic is unequivocally detected and measures an integrated flux of 1.2 ± 0.3 mJy. While the low-frequency (〈2 GHz) spectrum of the northern relic is well represented by a power law, it clearly steepens towards 16 GHz. This result is inconsistent with diffusive shock acceleration predictions of ageing plasma behind a uniform shock front. The steepening could be caused by an inhomogeneous medium with temperature/density gradients or by lower acceleration efficiencies of high energy electrons. Further modelling is necessary to explain the observed spectrum.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    FR II radio galaxies at low frequencies - I. Morphology, magnetic field strength and energetics (2016)
    Oxford University Press
    Details
    Publication Date: 2016-04-14
    Description: Due to their steep spectra, low-frequency observations of Fanaroff–Riley type II (FR II) radio galaxies potentially provide key insights in to the morphology, energetics and spectrum of these powerful radio sources. However, limitations imposed by the previous generation of radio interferometers at metre wavelengths have meant that this region of parameter space remains largely unexplored. In this paper, the first in a series examining FR IIs at low frequencies, we use LOFAR (LOw Frequency ARray) observations between 50 and 160 MHz, along with complementary archival radio and X-ray data, to explore the properties of two FR II sources, 3C 452 and 3C 223. We find that the morphology of 3C 452 is that of a standard FR II rather than of a double-double radio galaxy as had previously been suggested, with no remnant emission being observed beyond the active lobes. We find that the low-frequency integrated spectra of both sources are much steeper than expected based on traditional assumptions and, using synchrotron/inverse-Compton model fitting, show that the total energy content of the lobes is greater than previous estimates by a factor of around 5 for 3C 452 and 2 for 3C 223. We go on to discuss possible causes of these steeper-than-expected spectra and provide revised estimates of the internal pressures and magnetic field strengths for the intrinsically steep case. We find that the ratio between the equipartition magnetic field strengths and those derived through synchrotron/inverse-Compton model fitting remains consistent with previous findings and show that the observed departure from equipartition may in some cases provide a solution to the spectral versus dynamical age disparity.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    The impact of a young radio galaxy: clues from the cosmic ray electron population (2014)
    Oxford University Press
    Details
    Publication Date: 2014-03-09
    Description: 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 int  = 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.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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