Reionization and the Cosmic Dawn with the Square Kilometre Array

The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21 cm line from the earliest phases of star and galaxy formation in the Universe. This 21 cm signal provides a new and unique window both on the time of the formation of the first stars and accreting black holes and the subsequent period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical phenomena. Here we present a white paper with an overview of the science questions that SKA-low can address, how we plan to tackle these questions and what this implies for the basic design of the telescope.     

Garnet reaction rims from the breakdown of Staurolite in polymetamorphic micashists from the Rappold complex, Austroalpine basement, Eastern Alps

In polymetamorphic pelites of the Rappold complex in the Wölz crystalline basement (Eastern Alps) reaction rim garnets at staurolite-quartz interfaces (type I) and single grain garnets along previous staurolite-white mica interfaces (type II) were formed. The garnet reaction rims were formed during the Cretaceous amphibolite facies metamorphic overprint of the pre-existing mineral assemblages comprising garnet, staurolite, and kyanite from an amphibolite facies metamorphic event probably of Variscian age. The newly formed garnet may take the form of reaction rims along the margins of large pre-existing staurolite blasts. The initial growth increments of garnet have low grossular content, and reaction rim growth was controlled by the transfer of Fe, Mg and Mn components from the staurolite-garnet interface to the quartz-garnet interface. Later garnet growth increments have relatively high grossular content due to consumption of matrix plagioclase, which was destabilized by successive pressure increase. The grossular content of newly formed garnet shows systematic increase towards sites where plagioclase breaks down indicating that transport of calcium through the matrix was sluggish. On the basis of reaction microstructures it is demonstrated that the mineral assemblage garnet?+?kyanite?+?biotite?+?paragonite was formed at the conditions of eo-alpine amphibolite facies overprint while staurolite and plagioclase broke down successively with increasing pressure.     

Seasonal transport pattern of chromium(III and VI) in a stream receiving wastewater from tanneries

Water, suspended matter and sediment samples from a system heavily impacted by wastewater from numerous small tanneries (the upper Dunajec River, southern Poland) were collected to establish the annual cycle of Cr. To study possible oxidation processes the speciation of Cr and Mn concentrations were also investigated. This study showed that Cr(III and VI) temporal and spatial distributions are regulated by coupled anthropogenic (source location and emissions) and hydrologic factors (water flow and particle transport). Chromium(III) concentrations in all compartments varied seasonally as a function of the hydrological regime, production cycle in tanneries and distance from the discharge location. Cr(III) was largely associated with the particulate phase and rapidly deposited in river bed sediments. Contaminated river sediments were however flushed during flood periods to the reservoir located downstream from tanneries. During the tanning season (November to March), Chromium(III) concentrations in the water column and total Cr concentration in sediments exceeded relevant ecotoxicological guidelines only upstream from the reservoir, which trapped about 70% of the annual Cr(III) load transported by the Dunajec river. A correlation between Cr(VI)/Cr(III) ratios and Mn concentration in sediments downstream from the reservoir suggests the possibility of Cr(III) oxidation in natural conditions.     

Geochemistry of rare earth elements in a marine influenced coal and its organic solvent extracts from the Antaibao mining district, Shanxi, China

Twenty-six samples including roof, bottom and coal plies of a marine influenced coal bed were collected from the Antaibao mining district, Shanxi, China. The rare earth elements (REEs) were determined in solids and organic solvent extracts. The distribution pattern showed three distinct patterns: shale-like, LREE-rich and HREE-rich. This is attributed to the variable microenvironment of peat-forming swamp, the degree of marine influences and different REE sources. REEs in the coal are mainly controlled by detrital minerals but also affected by seawater. The chondrite-normalized REE patterns of the organic solvent extracts are distinctly different from those of corresponding original coal samples, which show a negative Eu anomaly, a depletion of middle REEs and an enrichment of HREEs. The LREEs in coal extracts are likely adsorbed by hydrogen-containing functional groups, and HREEs are likely bonded to carbon atoms.     

Evolution of the trophic state of Lake Annecy (eastern France) since the last glaciation as indicated by iron, manganese and phosphorus speciation

Lake Annecy sediments have been studied to provide an insight into the evolution of the lake trophic state in response to climate changes during the Holocene. Determination of the concentration of carbonate, Fe, Mn, and different forms of P in conjunction with total sediment fluxes derived from ¹⁴C ages allows an estimation of yearly fluxes of these sediment components. High fluxes of endogenic carbonate occur during the early to middle Holocene. Non apatitic inorganic phosphorus flux is variable but shows some higher-than-present values during this period. These observations are interpreted as being a result of enhanced productivity by favourable conditions for phytoplankton development. In addition, the low Mn/Fe ratio of the redox-sensitive forms of these elements recorded during this period suggests low oxygen concentrations in the bottom waters. Therefore it appears that the lake may have undergone oxygen depletion in the bottom water during the warmer-than-present periods, due to increased productivity and subsequent oxygen consumption from the decay of organic matter. With future climate changes, this suggests that lake water quality may likely degrade under global warming.     

No large-angle correlations on the non-Galactic microwave sky

We investigate the angular two-point correlation function of temperature in the Wilkinson Microwave Anisotropy Probe ( WMAP) maps. Updating and extending earlier results, we confirm the lack of correlations outside the Galaxy on angular scales greater than about 60° at a level that would occur in 0.025 per cent of realizations of the concordance model. This represents a dramatic increase in significance from the original observations by the Cosmic Background Explorer Differential Microwave Radiometer ( COBE-DMR) and a marked increase in significance from the first-year WMAP maps. Given the rest of the reported angular power spectrum   C _ℓ  , the lack of large-angle correlations that one infers outside the plane of the Galaxy requires covariance among the   C _ℓ  up to  ℓ= 5  . Alternately, it requires both the unusually small (5 per cent of realizations) full-sky large-angle correlations and an unusual coincidence of alignment of the Galaxy with the pattern of cosmological fluctuations (less than 2 per cent of those 5 per cent). We argue that unless there is some undiscovered systematic error in their collection or reduction, the data point towards a violation of statistical isotropy. The near-vanishing of the large-angle correlations in the cut-sky maps, together with their disagreement with results inferred from full-sky maps, remains open problems, and are very difficult to understand within the concordance model.     

Argon and CO2 on the race track in silicate melts: A tool for the development of a CO2 speciation and diffusion model

We have analysed the kinetics of Argon and CO₂ diffusion in simplified iron free rhyolitic to hawaiitic melts using the diffusion couple technique. The concentration distance profiles of Ar and CO₂ were measured with electron microprobe analysis and Fourier Transform Infrared Spectroscopy, respectively. Error functions were fitted to the symmetrical concentration distance profiles to extract the diffusion coefficients.In the temperature range 1373 to 1773 K the activation energies for Ar diffusion range from 169 ± 20 to 257 ± 62 kJ mol⁻¹. Ar diffusivity increases exponentially with the degree of depolymerisation. In contrast, the mobility of total CO₂, that is identical to Ar mobility in rhyolitic melt, keeps constant with changing bulk composition from rhyolite to hawaiite. CO₂ speciation at 1623 K and 500 MPa was modeled for the range of compositions studied using the diffusion data of Ar and total CO₂ in combination with network former diffusion calculated from viscosity data. Within error this model is in excellent agreement with CO₂ speciation data extrapolated from temperatures near the glass transition temperature for dacitic melt composition. This model shows that even in highly depolymerised hawaiitic and tholeiitic melts molecular CO₂ is a stable species and contributes 70 to 80% to the total CO₂ diffusion, respectively.