Cosmological perturbation theory and the spherical collapse model — III. The velocity divergence field and the Ω dependence

Cosmological perturbation theory (PT) is a useful tool to study the cumulants of the density and velocity fields in the large-scale structure of the Universe. In Papers I and II of this series we saw that the spherical collapse (SC) model provides the exact solution to PT at tree-level and gives a good approximation to the loop corrections (next-to-leading orders), indicating negligible tidal effects. Here, we derive predictions for the (smoothed) cumulants of the velocity divergence field θ ≡ ▽ ⊙  v for an irrotational fluid in the SC model. By comparing these with the exact analytic results of Scoccimarro &38; Frieman, it is shown that, at least for the unsmoothed case, the loop corrections to the cumulants of θ are dominated by tidal effects. However, most of the tidal contribution seems to cancel out when computing the hierarchical ratios, T _J  = 〈θ ^J 〉 / 〈θ²〉  ^{J −1}. We also extend the work presented in Papers I and II to give predictions for the cumulants of the density and velocity divergence fields in non-flat spaces. In particular, we show the equivalence between the spherically symmetric solution to the equations of motion in the SC model (given in terms of the density) and that of the Lagrangian PT approach (given in terms of the displacement field). It is shown that the Ω dependence is very weak for both cosmic fields even at one loop (a 10 per cent effect at most), except for the overall factor f (Ω) that couples to the velocity divergence.     

Organic carbon isotope ratios of recent sediments from coastal lagoons of the Gulf of Mexico,Mexico

The stable carbon isotope composition sedimentary organic carbon was determined in the sediments of seven coastal lagoons of the Gulf of Mexico, Mexico. For most of the lagoons the δ¹³C values for sediments ranged from ?20.1 to ?23.9%. Anomalously low values, ?26.8 to 29.3%. were determined in sediments of two of the studied lagoons, probably due to the presence of organic carbon from anthropogenic sources, naturally absent in these environments. The δ¹³C values determined in the tissues of oysters collected at the same time in the different lagoons were very similar to those recorded in the sediments.     

Spatial and temporal variations in aboveground and belowground biomass of Spartina maritima (small cordgrass) in created and natural marshes

Spartina species are commonly used for salt marsh manipulative projects, where aboveground and belowground biomasses are functional traits that play important roles, showing high spatial and temporal variations. This work analyses variations in AGB and BGB of Spartina maritima and abiotic environmental parameters along a chronosequence of six marshes created from 1997 to 2003 with disparate sediment dynamics, and adjacent natural marshes and unvegetated tidal flats. S. maritima behaved as an autogenic engineer, as its colonization of bare sediments yielded abiotic environmental changes: specifically, bed level rise accompanied by higher oxygenation and salinity. These modifications of the environment were site-specific, depending mainly on sedimentary dynamics. At the same time, abiotic environmental changes determined biomass production rates of S. maritima that were higher in more-accreting marshes; however, AGB was kept constant from early in its development (2 years). The increase in BGB with elevation seemed to be related to the inhibition of subsurface tissue development in anoxic sediments. Biomass accumulation and production varied markedly, depending on the spatial scale, indicating the relevance of the plot size chosen for the analysis of biomass of cordgrasses. Our results show that managers of salt marshes should consider sedimentary dynamics carefully when setting realistic expectations for success criteria of created and restored wetlands.     

Sea-level rise research and dialogue in North Carolina: Creating windows for policy change

Coastal areas are among the world's most vulnerable landscapes to impacts related to climate change, including inundation from sea-level rise (SLR), increased exposure to shoreline erosion, and greater frequency and intensity of storms. The status of research on the physical, ecological, and socio-economic effects of vulnerability to SLR and progress toward planning for its consequences varies from region to region worldwide. Here, we synthesize the results of three decades of SLR research and the development of coastal management policies in North Carolina, USA. We identify the major factors responsible for opening new policy ‘windows’ that address SLR, including how stakeholders have developed an increased understanding of the risks, the extent of public dialogue about potential response strategies, and advances in political receptivity to policy change. Research and policy progress in North Carolina continue to provide a model for other regions to help guide and evaluate the development of coastal policies.     

Statistical analysis of galaxy surveys – III. The non-linear clustering of red and blue galaxies in the 2dFGRS

We present measurements of the higher order clustering of red and blue galaxies as a function of scale and luminosity made from the two-degree field galaxy redshift survey (2dFGRS). We use a counts-in-cells analysis to estimate the volume-averaged correlation functions,     , as a function of scale up to the order of   p = 5  , and also the reduced void probability function. Hierarchical amplitudes are constructed using the estimates of the correlation functions:     . We find that (i) red galaxies display stronger clustering than blue galaxies at all orders measured; (ii) red galaxies show values of   S _p   that are strongly dependent on luminosity whereas blue galaxies show no segregation in   S _p   within the errors; this is remarkable given the segregation in the variance; (iii) the linear relative bias shows the opposite trend to the hierarchical amplitudes, with little segregation for the red sequence and some segregation for the blue; (iv) faint red galaxies deviate significantly from the 'universal' negative binomial reduced void probabilities followed by all other galaxy populations. Our results show that the characteristic colour of a galaxy population reveals a unique signature in its spatial distribution. Such signatures will hopefully further elucidate the physics responsible for shaping the cosmological evolution of galaxies.     

Phytoliths infer locally dense and heterogeneous paleovegetation at FLK North and surrounding localities during upper Bed I time, Olduvai Gorge, Tanzania

The phytolith content of 10 samples collected immediately under Tuff IF (~ 1.785 Ma) at FLK N and other surrounding localities (~ 2 km²) provides a direct botanical evidence for woody vegetation in the eastern margin of Olduvai Gorge during uppermost Bed I time. Observation and counting of 143 phytolith types (5 to >150 μ) reveal dense but heterogeneous woody cover (~ 40–90%) of unidentified trees and/or shrubs and palms associated to the freshwater springs surrounding FLK N, and more open formation (presumably ~ 25–70% woody cover) in the southeast at localities VEK, HWK W and HWK E. The paleovegetation is best described as groundwater palm forest/woodland or bushland, which current analogue may be found near Lake Manyara in similar hydrogeological context (freshwater springs near saline/alkaline lake). Re-evaluating the published pollen data based on this analogy shows that 70% of the pollen signal at FLK N may be attributed to thicket-woodland, Acacia groundwater woodland, gallery and groundwater forests; while < 30% is attributed to swamp herbage and grasslands. Micro-botanical, isotopic, and taphonomical studies of faunal remains converge on the same conclusion that the area surrounding FLK N, which attracted both carnivores and hominins in the early Pleistocene, was densely wooded during uppermost Bed I time.     

The real- and redshift-space density distribution functions for large-scale structure in the spherical collapse approximation

We use the spherical collapse (SC) approximation to derive expressions for the smoothed redshift-space probability distribution function (PDF), as well as the p -order hierarchical amplitudes S _p , in both real and redshift space. We compare our results with numerical simulations, focusing on the     standard CDM model, where redshift distortions are strongest. We find good agreement between the SC predictions and the numerical PDF in real space even for     , where σ _L is the linearly evolved rms fluctuation on the smoothing scale. In redshift space, reasonable agreement is possible only for     . Numerical simulations also yield a simple empirical relation between the real-space PDF and the redshift-space PDF: we find that for     , the redshift-space PDF, [ P δ _{( z )}], is, to a good approximation, a simple rescaling of the real-space PDF, P [ δ ], i.e.,     where σ and σ _{( z )} are the real-space and redshift-space rms fluctuations, respectively. This result applies well beyond the validity of linear perturbation theory, and it is a good fit for both the standard CDM model and the ΛCDM model. It breaks down for SCDM at     , but provides a good fit to the ΛCDM models for σ _L as large as 0.8.     

LEGRI instrument health. A historical review

LEGRI has been operating successfully on MINISAT-01 since its switch-on the 22nd of May 1997. HouseKeeping (HK) data have been continuously receivedfor nearly two years by LEGRI SOC in Valencia, and subsequently checked on adaily basis and then stored for long term monitoring analysis.LEGRI HouseKeeping data include three critical operating parameters:temperature, power and polarisation voltages. Six temperature sensors arespread over the different LEGRI units: Detector Unit, Data Processing Unit,High Voltage Unit and Star Sensor. Voltages are measured at eight differentpoints. Detector Unit temperature and polarisation voltage are thecritical parameters for LEGRI operation. Solid state detectors aresensitive to changes not only in polarisation but also in temperature.Around one and a half million of measurements for each of the HK fourteen parameters have been recorded and analysed. The data show a very remarkablestability, within the expected margins, and the averages are very close to theoptimal design values. Special attention has been paid to the detectorpolarisation voltages analysis with a mean value of 286 ± 2 V when the detectors are operating. Thermal control over all the LEGRI units shows a remarkable stability in their temperatures.On the detector plane a mean value of T _det = 13 ± 2 ^°C has been found.We can therefore conclude that LEGRI as a system has been operating withinits optimal design conditions. We also want to point out the excellentperformance of the MINISAT-01 thermal control system.     

Long-Term Evolution of the Seismic Activity Preceding the 2015 Seismic Crisis at Deception Island Volcano,Antarctica (2008-2015)

Surveys in Geophysics - Deception Island is an active volcano located in the South Shetland Islands, Antarctica. Although the last eruptions occurred in 1967-1970, the volcano has undergone periods...