The effect of primordial non-Gaussianity on the topology of large-scale structure     

C. Hikage  P. Coles  M. Grossi  L. Moscardini  K. Dolag  E. Branchini  S. Matarrese 《Monthly notices of the Royal Astronomical Society》2008,385(3):1613-1620

We study the effect of primordial non-Gaussianity on the development of large-scale cosmic structure using high-resolution N -body simulations. In particular, we focus on the topological properties of the 'cosmic web', quantitatively characterized by the Minkowski functionals (MFs), for models with quadratic non-linearities with different values of the usual non-Gaussianity parameter f _NL. In the weakly non-linear regime (the amplitude of mass density fluctuations σ₀ < 0.1), we find that analytic formulae derived from perturbation theory agree with the numerical results within a few per cent of the amplitude of each MF when | f _NL| < 1000. In the non-linear regime, the detailed behaviour of the MFs as functions of threshold density deviates more strongly from the analytical curves, while the overall amplitude of the primordial non-Gaussian effect remains comparable to the perturbative prediction. When smaller-scale information is included, the influence of primordial non-Gaussianity becomes increasingly significant statistically due to decreasing sample variance. We find that the effect of the primordial non-Gaussianity with  | f _NL| = 50  is comparable to the sample variance of mass density fields with a volume of 0.125( h ⁻¹ Gpc)³ when they are smoothed by Gaussian filter at a scale of 5  h ⁻¹ Mpc. The detectability of this effect in actual galaxy surveys will strongly depend on residual uncertainties in cosmological parameters and galaxy biasing.  相似文献   

Surface brightness measurements for APM galaxies     

Z. Shao  S. J. Maddox  J. B. Jones  P. Coles 《Monthly notices of the Royal Astronomical Society》2003,338(1):72-84

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The cluster distribution as a test of dark matter models — IV. Topology and geometry     

Coles  Pearson  Borgani  Plionis  & Moscardini 《Monthly notices of the Royal Astronomical Society》1998,294(2):245-258

We study the geometry and topology of the large-scale structure traced by galaxy clusters in numerical simulations of a box of side 320 h ⁻¹ Mpc, and compare them with available data on real clusters. The simulations we use are generated by the Zel'dovich approximation, using the same methods as we have used in the first three papers in this series. We consider the following models to see if there are measurable differences in the topology and geometry of the superclustering they produce: (i) the standard cold dark matter model (SCDM); (ii) a CDM model with Ω₀ = 0.2 (OCDM); (iii) a CDM model with a 'tilted' power spectrum having n  = 0.7 (TCDM); (iv) a CDM model with a very low Hubble constant, h  = 0.3 (LOWH); (v) a model with mixed CDM and HDM (CHDM); (vi) a flat low-density CDM model with Ω₀ = 0.2 and a non-zero cosmological Λ term (ΛCDM). We analyse these models using a variety of statistical tests based on the analysis of: (i) the Euler–Poincaré characteristic; (ii) percolation properties; (iii) the minimal spanning tree construction. Taking all these tests together we find that the best-fitting model is ΛCDM and, indeed, the others do not appear to be consistent with the data. Our results demonstrate that despite their biased and extremely sparse sampling of the cosmological density field, it is possible to use clusters to probe subtle statistical diagnostics of models, which go far beyond the low-order correlation functions usually applied to study superclustering.  相似文献   

A bimodal model of the solar wind speed     

W. A. Coles 《Astrophysics and Space Science》1996,243(1):87-96

Until the ULYSSES spacecraft reached high latitude, the only means for measuring the solar wind velocity in the polar regions was from radio scattering observations (IPS), and these remain the only way to measure the velocity near the sun. However, IPS, like many remote sensing observations, is a line-of-sight integrated measurement. This integration is particularly troublesome when the line-of-sight passes through a fast stream but that stream does not occupy the entire scattering region. Observations from the HELIOS spacecraft have shown that the solar wind has a bimodal character which becomes more pronounced near the sun. Recent observations from ULYSSES have confirmed that this structure is clear at high latitudes even at relatively large solar distances. We have developed a method of separating the fast and slow contributions to an IPS observation which takes advantage of this bimodal structure. In this paper I will describe the technique and its application to IPS observations made using the receiving antennas of the EISCAT incoherent backscatter radar observatory in northern Scandinavia.  相似文献   

Weak lensing from strong clustering     

Dipak Munshi  Peter Coles 《Monthly notices of the Royal Astronomical Society》2000,313(1):148-152

We investigate the effect of weak gravitational lensing in the limit of small angular scales where projected galaxy clustering is strongly non-linear. This is the regime likely to be probed by future weak lensing surveys. We use well-motivated hierarchical scaling arguments and the plane-parallel approximation to study multi-point statistical properties of the convergence field. These statistics can be used to compute the vertex amplitudes in tree models of hierarchical clustering; these can be compared with similar measurements from galaxy surveys, leading to a powerful probe of galaxy bias.  相似文献   

Times for (Un)sustainability? Challenges and opportunities for developing behaviour change policy. A case-study of consumers at home and away     

Stewart Barr  Gareth Shaw  Tim Coles 《Global Environmental Change》2011,21(4):1234-1244

This paper examines the assertion that individuals with seemingly high levels of commitment to the environment at home may also be those engaged in less sustainable leisure and tourism behaviours, including a high dependency on air travel. This potential difference in environmental commitments between different consumption settings is placed within the context of recent policy developments that have seen the rise of segmentation as a commonly applied technique used to understand and encourage pro-environmental behaviours through the notion of ‘sustainable lifestyles’ and social marketing campaigns. Using data derived from a questionnaire of consumers in the UK, three distinctive, empirically-defined ‘lifestyle’ groups are identified, based on the respondents’ environmental behaviours. Significant differences emerged in reported environmental commitments according to their consumption setting. Those with higher levels of commitment in and around the home also tended to be those who flew furthest and most frequently, whilst those with moderate-to-high commitments ‘at home’ often failed to transfer these activities to their holiday environments. The paper concludes by arguing that both academics and policy-makers need to address the role of different consumption settings in which behaviours are undertaken and the ways in which these relate to underlying social practices within these settings.  相似文献   

Variable Tl,Pb, and Cd concentrations and isotope compositions of enstatite and ordinary chondrites—Evidence for volatile element mobilization and decay of extinct 205Pb          下载免费PDF全文

Emeliana Palk  Rasmus Andreasen  Mark Rehkämper  Alison Stunt  Katharina Kreissig  Barry Coles  Maria Schönbächler  Caroline Smith 《Meteoritics & planetary science》2018,53(2):167-186

New Tl, Pb, and Cd concentration and Tl, Pb isotope data are presented for enstatite as well as L- and LL-type ordinary chondrites, with additional Cd stable isotope results for the former. All three chondrite suites have Tl and Cd contents that vary by more than 1–2 orders of magnitude but Pb concentrations are more uniform, as a result of terrestrial Pb contamination. Model calculations based on Pb isotope compositions indicate that for more than half of the samples, more than 50% of the measured Pb contents are due to addition of modern terrestrial Pb. In part, this is responsible for the relatively young and imprecise Pb-Pb ages determined for EH, L, and LL chondrites, which are hence only of limited chronological utility. In contrast, four particularly pristine EL chondrites define a precise Pb-Pb cooling age of 4559 ± 6 Ma. The enstatite chondrites (ECs) have highly variable ε^114/110Cd of between about +3 and +70 due to stable isotope fractionation from thermal and shock metamorphism. Furthermore, nearly all enstatite meteorites display ε²⁰⁵Tl values from −3.3 to +0.8, while a single anomalous sample is highly fractionated in both Tl and Cd isotopes. The majority of the ECs thereby define a correlation of ε²⁰⁵Tl with ε^114/110Cd, which suggests that at least some of the Tl isotope variability reflects stable isotope fractionation rather than radiogenic ingrowth of ²⁰⁵Tl from ²⁰⁵Pb decay. Considering L chondrites, most ε²⁰⁵Tl values range between −4 and +1, while two outliers with ε²⁰⁵Tl ≤ −10 are indicative of stable isotope fractionation. Considering only those L chondrites which are least likely to feature Pb contamination or stable Tl isotope effects, the results are in accord with the former presence of live ²⁰⁵Pb on the parent body, with an initial ²⁰⁵Pb/²⁰⁴Pb = (1.5 ± 1.4) × 10⁻⁴, which suggests late equilibration of the Pb-Tl system 26–113 Ma after carbonaceous chondrites (CCs). The LL chondrites display highly variable ε²⁰⁵Tl values from −12.5 to +14.9, also indicative of stable isotope effects. However, the data for three pristine LL3/LL4 chondrites display an excellent correlation between ε²⁰⁵Tl and ²⁰⁴Pb/²⁰³Tl. This defines an initial ²⁰⁵Pb/²⁰⁴Pb of (1.4 ± 0.3) × 10⁻⁴, equivalent to a ²⁰⁵Pb-²⁰⁵Tl cooling age of 55 + 12/−24 Ma (31–67 Ma) after CCs.  相似文献   

Rare earth element and Pb isotope variations in a 52 kyr peat core from Lynch’s Crater (NE Queensland, Australia): Proxy development and application to paleoclimate in the Southern Hemisphere     

M.E. Kylander  J. Muller  K. Gallagher  B.J. Coles  D.J. Weiss 《Geochimica et cosmochimica acta》2007,71(4):942-960

Accurate prediction of future climate scenarios is contingent on our understanding of past and present climate mechanisms. This is done in part through the reconstruction of historical climate changes using proxy records from terrestrial and marine archives. Terrestrial archives covering the Holocene and late Pleistocene are limited, most acutely in the Southern Hemisphere. Here, Rare earth elements (REE) and Pb isotopes are developed as inorganic geochemical proxies of mineral dust source changes and, by extension, climate change. Using a peat core from Lynch’s Crater in NE Queensland, Australia, we present the first long-term (c. 52 kyr) terrestrial record of atmospheric REE and Pb deposition (with the exception of four wet events which represent periods of erosion from the crater itself) in the Southern Hemisphere covering both glacial and interglacial times. Based on a combination of correlation analyses, Al and Ti normalised profiles and elemental patterns, we establish REE are immobile within the peat deposit and not subject to significant post depositional diagenetic changes (important particularly for Ce). This is vital as REE can be mobile under acid and organic rich conditions like those that can occur during the development of a peat deposit. The volcanic provinces of eastern Australia have characteristic Eu anomaly signatures, which allowed their use in a novel way to detect changes in dust source to Lynch’s Crater. Between 41,095 and 52,505 BP the deposit was under the influence of dust carried by long distance transport (>1500 km) from SE Australia. From 8525 to 40,815 BP regional sources (100-1500 km) dominated the deposited signals while between 1740 and 8390 BP the dust signal was controlled by local sources (<100 km). These findings were also confirmed by Pb isotope data. Changepoint modelling refined the timing of these changes in dust source, recognizing concurrent shifts in our tracing tools ((Eu/Eu^∗)_PAAS and ²⁰⁶Pb/²⁰⁷Pb). These changepoints were then compared to other palaeoenvironmental records (pollen, lake levels and dune building) from eastern Australia and found to be similar. Our results demonstrate that REE and Pb isotopes are effective tools for tracing past changes in atmospheric dust sources and to the study of climate change using minerotrophic peat deposits.  相似文献   

Statistical cosmollogy in retrospect     

Peter Coles 《Astronomy& Geophysics》2003,44(3):3.16-3.20

Peter Coles looks at the past, present and future association of astronomy and cosmology with statistical theory.  相似文献   

The clustering of Lyman-break galaxies     

Peter Coles  Francesco Lucchin  Sabino Matarrese  & Lauro Moscardini 《Monthly notices of the Royal Astronomical Society》1998,300(1):183-187

We calculate the statistical clustering of Lyman-break galaxies predicted in a selection of currently fashionable structure formation scenarios. These models are all based on the cold dark matter model, but vary in the amount of dark matter, the initial perturbation spectrum, the background cosmology and the presence or absence of a cosmological constant term. If Lyman-break galaxies form as a result of hierarchical merging, the amplitude of clustering depends quite sensitively on the minimum halo mass that can host such a galaxy. Interpretation of the recent observations by Giavalisco et al. would therefore be considerably clarified by a direct determination of the relevant halo properties. For a typical halo mass around 10¹¹  h ⁻¹ M⊙ the observations do not discriminate strongly between cosmological models, but if the appropriate mass is larger, say 10¹²  h ⁻¹ M⊙ (which seems likely on theoretical grounds), then the data strongly favour models with a low matter density.  相似文献