388 research outputs found

    The Dynamical State and Mass-Concentration Relation of Galaxy Clusters

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    We use the Millennium Simulation series to study how the dynamical state of dark matter halos affects the relation between mass and concentration. We find that a large fraction of massive systems are identified when they are substantially out of equilibrium and in a particular phase of their dynamical evolution: the more massive the halo, the more likely it is found at a transient stage of high concentration. This state reflects the recent assembly of massive halos and corresponds to the first pericentric passage of recently-accreted material when, before virialization, the kinetic and potential energies reach maximum and minimum values, respectively. This result explains the puzzling upturn in the mass-concentration relation reported in recent work for massive halos; indeed, the upturn disappears when only dynamically-relaxed systems are considered in the analysis. Our results warn against applying simple equilibrium models to describe the structure of rare, massive galaxy clusters and urges caution when extrapolating scaling laws calibrated on lower-mass systems, where such deviations from equilibrium are less common. The evolving dynamical state of galaxy clusters ought to be carefully taken into account if cluster studies are to provide precise cosmological constraints.Comment: 8 Pages. Minor changes to match published versio

    Rapid remediation of sandy sulfuric subsoils using straw-derived dissolved organic matter

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    When acid sulfate soils dry, oxidation of pyrite can cause acidification and formation of iron (Fe) oxyhydroxy sulfate phases such as jarosite. Remediation via re-establishment of reducing conditions requires submergence and addition of biodegradable organic carbon (OC) to stimulate activity of reducing bacteria. Addition of fresh plant litter has been shown to activate reducing bacteria, likely due to the release of readily available soluble organic matter. However, the effectiveness of soluble organic matter from plant residues has not been tested yet. Here, we tested the potential of wheat straw-derived dissolved OC (DOC) for remediation of a sandy sulfuric (pH < 4) soil. In a second set of experiments, we used combinations of wheat straw-derived DOC with lactate, which is a preferred substrate of sulfate reducing bacteria. All incubation experiments were conducted in the dark at 20 °C. The results showed that addition of DOC from wheat straw induces reduction reactions and rapidly increases the pH by 2–3 units after 3 weeks of incubation under submerged conditions. Mössbauer spectroscopy and X-ray diffraction revealed that jarosite was lost after 200 days of anoxic incubation. Short range-ordered FeIII oxyhydroxides were formed, most likely by FeII-catalysed transformation of jarosite. A second addition of DOC, as well as the addition of lactate, resulted in the almost complete loss of jarosite with increased proportions of FeIII oxyhydroxides in the remaining solids, but not in the formation of FeII sulfides. The formation of FeIII oxyhydroxides reduces the risk of both Fe leaching and renewed acidification in the event of future oxidation. The results suggest that deep injection of wheat straw-derived DOC is a promising approach for rapid and sustainable remediation of sandy sulfuric subsoils. © 2022 The Author
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