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Ravi K. Sheth 《Monthly notices of the Royal Astronomical Society》1998,300(4):1057-1070
A model of the gravitationally evolved dark matter distribution, in the Eulerian space, is developed. It is a simple extension of the excursion set model that is commonly used to estimate the mass function of collapsed dark matter haloes. In addition to describing the evolution of the Eulerian space distribution of the haloes, the model allows one to describe the evolution of the dark matter itself. It can also be used to describe density profiles, on scales larger than the virial radius of these haloes, and to quantify the way in which matter flows in and out of Eulerian cells. When the initial Lagrangian space distribution is white noise Gaussian, the model suggests that the Inverse Gaussian distribution should provide a reasonably good approximation to the evolved Eulerian density field, in agreement with numerical simulations. Application of this model to clustering from more general Gaussian initial conditions is discussed at the end. 相似文献
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Jörg M. Colberg Ravi K. Sheth Antonaldo Diaferio Liang Gao Naoki Yoshida 《Monthly notices of the Royal Astronomical Society》2005,360(1):216-226
We study the formation and evolution of voids in the dark matter distribution using various simulations of the popular Λ cold dark matter cosmogony. We identify voids by requiring them to be regions of space with a mean overdensity of −0.8 or less – roughly the equivalent of using a spherical overdensity group finder for haloes. Each of the simulations contains thousands of voids. The distribution of void sizes in the different simulations shows good agreement when differences in particle and grid resolution are accounted for. Voids very clearly correspond to minima in the smoothed initial density field. Apart from a very weak dependence on the mass resolution, the rescaled mass profiles of voids in the different simulations agree remarkably well. We find a universal void mass profile of the form ρ(< r )/ρ( r eff ) ∝ exp[( r / r eff )α ] , where r eff is the effective radius of a void and α∼ 2 . The mass function of haloes in voids is steeper than that of haloes that populate denser regions. In addition, the abundances of void haloes seem to evolve somewhat more strongly between redshifts ∼1 and 0 than the global abundances of haloes. 相似文献
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We use the spherical evolution approximation to investigate non-linear evolution from the non-Gaussian initial conditions characteristic of the local f nl model. We provide an analytic formula for the non-linearly evolved probability distribution function (PDF) of the dark matter which shows that the underdense tail of the non-linear PDF in the f nl model should differ significantly from that for Gaussian initial conditions. Measurements of the underdense tail in numerical simulations may be affected by discreteness effects, and we use a Poisson counting model to describe this effect. Once this has been accounted, our model is in good quantitative agreement with the simulations. In principle, our calculation is an important first step in programs which seek to reconstruct the shape of the initial PDF from observations of large-scale structures in the Lyα forest and the galaxy distribution at later times. 相似文献
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Graziano Rossi Ravi K. Sheth Changbom Park Carlos Hernández-Monteagudo 《Monthly notices of the Royal Astronomical Society》2009,399(1):304-316
We present measurements of the clustering of hot and cold patches in the microwave background sky as measured from the Wilkinson Microwave Anisotropy Probe 5-year data. These measurements are compared with theoretical predictions which assume that the cosmological signal obeys Gaussian statistics. We find significant differences from the simplest Gaussian-based prediction. However, the measurements are sensitive to the fact that the noise is spatially inhomogeneous (e.g. because different parts of the sky were observed for different lengths of time). We show how to account for this spatial inhomogeneity when making predictions. Differences from the Gaussian-based expectation remain even after this more careful accounting of the noise. In particular, we note that hot and cold pixels cluster differently within the same temperature thresholds at few-degree scales. While these findings may indicate primordial non-Gaussianity, we discuss other plausible explanations for these discrepancies. In addition, we find some deviations from Gaussianity at sub-degree scales, especially in the W band, whose origin may be associated with extragalactic dust emission. 相似文献
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Highly heterogeneous Precambrian basement under the central Deccan Traps, India: Direct evidence from xenoliths in dykes 总被引：1，自引：0，他引：1
Ranjini Ray Anil D. Shukla Hetu C. Sheth Jyotiranjan S. Ray Raymond A. Duraiswami Loyc Vanderkluysen Chandramohan S. Rautela Jyotirmoy Mallik 《Gondwana Research》2008,13(3):375-385
Crustal or mantle xenoliths are not common in evolved, tholeiitic flood basalts that cover huge areas of the Precambrian shields. Yet, the occasional occurrences provide the most direct and unequivocal evidence on basement composition. Few xenolith occurrences are known from the Deccan Traps, India, and inferences about the Deccan basement have necessarily depended on geophysical studies and geochemistry of Deccan lavas and intrusions. Here, we report two basalt dykes (Rajmane and Talwade dykes) from the central Deccan Traps that are extremely rich in crustal xenoliths of great lithological variety (gneisses, quartzites, granite mylonite, felsic granulite, carbonate rock, tuff). Because the dykes are parallel and only 4 km apart, and only a few kilometres long, the xenoliths provide clear evidence for high small-scale lithological heterogeneity and strong tectonic deformation in the Precambrian Indian crust beneath. Measured 87Sr/86Sr ratios in the xenoliths range from 0.70935 (carbonate) to 0.78479 (granite mylonite). The Rajmane dyke sampled away from any of the xenoliths shows a present-day 87Sr/86Sr ratio of 0.70465 and initial (at 66 Ma) ratio of 0.70445. The dyke is subalkalic and fairly evolved (Mg No. = 44.1) and broadly similar in its Sr-isotopic and elemental composition to some of the lavas of the Mahabaleshwar Formation. The xenoliths are comparable lithologically and geochemically to basement rocks from the Archaean Dharwar craton forming much of southern India. As several lines of evidence suggest, the Dharwar craton may extend at least 350–400 km north under the Deccan lava cover. This is significant for Precambrian crustal evolution of India besides continental reconstructions. 相似文献