The polarization of scattered Lyα radiation around high-redshift galaxies

The high-redshift Universe contains luminous Lyα emitting sources such as galaxies and quasars. The emitted Lyα radiation is often scattered by surrounding neutral hydrogen atoms. We show that the scattered Lyα radiation obtains a high level of polarization for a wide range of likely environments of high-redshift galaxies. For example, the backscattered Lyα flux observed from galaxies surrounded by a superwind-driven outflow may reach a fractional polarization as high as ∼40 per cent. Equal levels of polarization may be observed from neutral collapsing protogalaxies. Resonant scattering in the diffuse intergalactic medium typically results in a lower polarization amplitude (≲7 per cent), which depends on the flux of the ionizing background. Spectral polarimetry can differentiate between Lyα scattering off infalling gas and outflowing gas; for an outflow, the polarization should increase towards longer wavelengths while for infall the opposite is true. Our numerical results suggest that Lyα polarimetry is feasible with existing instruments, and may provide a new diagnostic of the distribution and kinematics of neutral hydrogen around high-redshift galaxies. Moreover, polarimetry may help suppress infrared lines originating in the Earth's atmosphere, and thus improve the sensitivity of ground-based observations to high-redshift Lyα emitting galaxies outside the currently available redshift windows.     

Eifelite,KNa3Mg4Si12O30, a new mineral of the osumilite group with octahedral sodium

Eifelite of variable composition is uniaxial positive withn ₀ near 1.543 andn _e near 1.544, a between 10.14 and 10.15 Å, andc about 14.22 Å, space groupP 6/m 2/c 2/c. There is a complete series of solid solution between the eifelite end member KNa₃Mg₄Si₁₂O₃₀ and roedderite, KNaMg₅Si₁₂O₃₀, following the 2 Na?Mg substitution. Both eifelite and roedderite have milarite-type structures, but Na is always in six-coordinated sites: In roedderite Na occupies solely a newly defined B′^[6]-position which is slightly displaced alongc from the ideal B_[9]-position lying on the (001/2)-mirror plane in K₂Mg₅Si₁₂O₃₀. In eifelite Na is located both inB′^[6] and in theA _[6]-positions, where it partially replaces Mg. Eifelite has the highest cation occupancy of all osumilite group minerals known thus far. Both eifelite and roedderite occur in vesicles of contact metamorphosed basement xenoliths ejected with the leucite tephrite lava of the Quaternary Bellerberg volcano in the Eifel, West Germany. They are considered to be precipitates from highly alkaline, MgSi-rich, but Al-deficient gas phases that originated through interaction of gaseous igneous differentiates with the xenoliths.     

Modelling discharge from a coastal watershed in southeast Sweden using an integrated framework

The field hydrology model DRAINMOD integrated with Arc Hydro in geographical information system (GIS) framework (Arc Hydro–DRAINMOD) was used to simulate the hydrological response of a coastal watershed in southeast Sweden. Arc Hydro–DRAINMOD uses a distributed approach to route water from each field edge to the watershed outlet. In the framework the Arc Hydro data model was used to describe the stream network in the watershed and to connect the individual simulated DRAINMOD‐field outflow time series from each plot using Arc Hydro schema‐links features, which were summed at Arc Hydro schema‐nodes features along the stream network to generate the stream network flow. Hydrology data collected during six periods between 2003 and 2008 were used to test Arc Hydro–DRAINMOD and its performance was evaluated by considering uncertainties in model inputs using generalized likelihood uncertainty estimation (GLUE). The GLUE estimates obtained (uncertainty bands 5% and 95%) agreed satisfactorily with measured monthly discharges. The percentage of time in which the observed discharges were bracketed by the uncertainty bands was 88% in calibration periods and 75% in validation periods. Although monthly time step simulations showed good agreement with observed discharges during the two main discharge events in spring, the contradictory daily time step results indicate that the watershed response simulations on a daily basis need to be improved. The uncertainty analysis showed that in periods of higher discharge, such as spring periods, the uncertainty in prediction was higher. It is important to note that these uncertainty estimations using the GLUE procedure include the uncertainties in measured discharge values, model inputs, boundary conditions and model structures. It was estimated that stream baseflow represented 42% of the total watershed discharge, but further research is needed to confirm this. These results show that the new Arc Hydro–DRAINMOD framework is applicable for predicting discharge from artificially drained watersheds in southeast Sweden. Copyright © 2010 John Wiley & Sons, Ltd.     

Semi‐Arid Aquifer Responses to Forest Restoration Treatments and Climate Change

The purpose of this study was to develop an interpretive groundwater‐flow model to assess the impacts that planned forest restoration treatments and anticipated climate change will have on large regional, deep (>400 m), semi‐arid aquifers. Simulations were conducted to examine how tree basal area reductions impact groundwater recharge from historic conditions to 2099. Novel spatial analyses were conducted to determine areas and rates of potential increases in groundwater recharge. Changes in recharge were applied to the model by identifying zones of basal area reduction from planned forest restoration treatments and applying recharge‐change factors to these zones. Over a 10‐year period of forest restoration treatment, a 2.8% increase in recharge to one adjacent groundwater basin (the Verde Valley sub‐basin) was estimated, compared to conditions that existed from 2000 to 2005. However, this increase in recharge was assumed to quickly decline after treatment due to regrowth of vegetation and forest underbrush and their associated increased evapotranspiration. Furthermore, simulated increases in groundwater recharge were masked by decreases in water levels, stream baseflow, and groundwater storage resulting from surface water diversions and groundwater pumping. These results indicate that there is an imbalance between water supply and demand in this regional, semi‐arid aquifer. Current water management practices may not be sustainable into the far future and comprehensive action should be taken to minimize this water budget imbalance.     

Mutual phenomena of Jupiter's satellites

Observations of an occultation of Europa by Io are fitted by a model light curve. The model has five free parameters, namely the radius of Europa, the impact parameter, the brightness ratio of the satellites, the time of midevent and the mean relative velocity. The model assumes a fixed value for the radius of Io and for the solar phase angle α, and that Europa has a uniform surface brightness. The OC residuals of the best fitting light curve are very small (～0.002 mag) and of a purely random nature; there is no evidence of albedo features. Taking α = 0 does not affect significantly the quality of the fit. Six mutual eclipses were also observed, and their times of minima agree well with the predictions of Aksnes Icarus21 (1974). For two events these predictions differ by about 20 min from those of Brinkmann and Millis Sky & Telescope45 (1973).     

High-magnesium staurolite in a sapphirine-garnet rock from the Limpopo Belt,Southern Africa

Unusually Mg-rich staurolite with F=Fe/(Fe+ Mg) = 0.51 occurs in a peraluminous silica-deficient sapphirine-garnet-gedrite-spinel-corundum-phlogopite rock as relic inclusions within pyrope-almandine garnet (F=0.43–0.48), from which it is generally separated by sapphirine (F=0.19). Gedrite has F=0.24–0.27, phlogopite 0.19, and spinel 0.43. The gradual disappearance of staurolite is due to a shift of the 3-phase AFM assemblage staurolite-garnetsapphirine to more Fe-rich compositions according to probably prograde reactions between staurolite and garnet to form sapphirine together with either quartz or gedrite. Thus still more Mg-rich staurolite seems to have existed in the rock at earlier stages of metamorphism characterized by lower temperatures and perhaps higher pressures. The local equilibria now frozen in indicate minimum pressures of 7–8 kbar and temperatures in excess of about 800° C.Staurolite is free from Zn, very low in Si, and richer in Ti than any other staurolite found thus far. Most notable is the unique Mg/Fe fraction between staurolite and garnet with staurolite being the more Fe-rich phase (K_D=1.32).     

Did dilution limit the phytoplankton response to iron addition in HNLCLSi sub-Antarctic waters during the SAGE experiment?

An in situ iron addition experiment (SAGE) was carried out in high-nitrate low-chlorophyll low-silicic acid (HNLCLSi) sub-Antarctic surface waters south-east of New Zealand. In contrast to other iron addition experiments, the phytoplankton response was minor, with a doubling of biomass relative to surrounding waters, with the temporal trends in dissolved iron and macronutrients instead dominated by physical factors such as mixing and dilution. The initial increase in patch surface area indicated a lateral dilution rate of 0.125 d⁻¹, with a second estimate from a model of the decline in peak SF₆ concentration yielding a higher lateral dilution rate of 0.16-0.25 d⁻¹. The model was tested on the SOIREE SF₆ dataset and provided a lateral dilution of 0.07 d⁻¹, consistent with previous published estimates. MODIS ocean colour images showed elevated chlorophyll coincident with the SF₆ patch on day 10 and 12, and an elevated chlorophyll filament at the SAGE experiment location 3-4 days after ship departure, which provided additional lateral dilution estimates of 0.19 and 0.128 d⁻¹. Dissolved iron at the patch centre declined by 85% within two days of the initial infusion, of which dilution accounted for 50-65%; it also decreased rapidly after the 2nd and 3rd infusions but remained elevated after the fourth infusion. Despite decreases in nitrate and silicic acid from day 7 and 10, respectively, the final nutrient concentrations in the patch exceeded the initial concentrations due to supply from lateral intrusion and mixed-layer deepening. The low Si:N loss ratio suggested that the observed limited response to iron was primarily by non-siliceous phytoplankton. Algal growth rate exceeded the minimum dilution rate during two periods (days 3-6 and 10-14), and coincided with net chlorophyll accumulation. However, as the ratio of algal growth to dilution was the lowest reported for an iron addition experiment, dilution was clearly a significant factor in the SAGE experiment recording the lowest phytoplankton response to mesoscale iron addition.     

The correlation between star formation and 21-cm emission during the reionization epoch

Reionization is thought to be dominated by low-mass galaxies, while direct observations of resolved galaxies probe only the most massive, rarest objects. The cross-correlation between fluctuations in the surface brightness of the cumulative Lyα emission (which serves as a proxy for the star formation rate) and the redshifted 21-cm signal from neutral hydrogen in the intergalactic medium (IGM) will directly probe the causal link between the production of ionizing photons in galaxies and the reionization of the IGM. We discuss the prospects for detecting this cross-correlation for unresolved galaxies. We find that on angular scales ≲10 arcmin detection will be practical using wide-field near-infrared (near-IR) imaging from space in combination with the forthcoming Mileura Wide-field Array – Low Frequency Demonstrator. When redshifted 21-cm observations of the neutral IGM are combined with space-based near-IR imaging of Lyα emission, the detection on angular scales ≲3 arcmin will be limited by the sensitivity of the 21-cm signal, even when a small-aperture optical telescope (∼2 m) and a moderate field of view (∼10 deg²) are used. On scales ≳3 arcmin, the measurement of cross-correlation will be limited by the accuracy of the foreground sky subtraction.