Universality of the Network and Bubble Topology in Cosmological Gravitational Simulations

Using percolation statistics we, for the first time, demonstrate the universal character of a network pattern in the real space, mass distributions resulting from nonlinear gravitational instability of initial Gaussian fluctuations. Percolation analysis of five stages of the nonlinear evolution of five power law models reveals that all models show a shift toward a network topology if seen with high enough resolution. However, quantitatively, the shift is significantly different in different models: the smaller the spectral index ,n, the stronger the shift. On the contrary, the shift toward the "bubble" topology is characteristic only for the n <= -1 models. We find that the mean density of the percolating structures in the nonlinear density distributions generally is very different from the density threshold used to identify them and corresponds much better to a visual impression. We also find that the maximum of the number of structures (connected regions above or below a specified density threshold) in the evolved, nonlinear distributions is always smaller than in Gaussian fields with the same spectrum, and is determined by the effective slope at the cutoff frequency.Comment: The paper is 26 pages long. The latex file uses aasms.sty as a style file. There are 5 figures and 2 tables included

The Effects of Redshift Distortions on Percolation Analysis

A report submitted by Capp Yess and Bill Criss to the Research and Creative Productions Committee in 1999 on the effects of Redshift Distortions on Percolation Analysis

Evidence for Filamentarity in the Las Campanas Redshift Survey

We apply Shapefinders, statistical measures of `shape' constructed from two dimensional partial Minkowski functionals, to study the degree of filamentarity in the Las Campanas Redshift Survey (LCRS). In two dimensions, three Minkowski functionals characterise the morphology of an object, they are: its perimeter (L), area (S), and genus. Out of L and S a single dimensionless Shapefinder Statistic, F can be constructed (0 <=F <=1). F acquires extreme values on a circle (F = 0) and a filament (F = 1). Using F, we quantify the extent of filamentarity in the LCRS by comparing our results with a Poisson distribution with similar geometrical properties and having the same selection function as the survey. Our results unambiguously demonstrate that the LCRS displays a high degree of filamentarity both in the Northern and Southern galactic sections a result that is in general agreement with the visual appearance of the catalogue. It is well known that gravitational clustering from Gaussian initial conditions gives rise to the development of non-Gaussianity reflected in the formation of a network-like filamentary structure on supercluster scales. Consequently the fact that the smoothed LCRS catalogue shows properties consistent with those of a Gaussian random field (Colley 1997) whereas the unsmoothed catalogue demonstrates the presence of filamentarity lends strong support to the conjecture that the large scale clustering of galaxies is driven by gravitational instability.Comment: Accepted for publication in Ap

Evidence for Filamentarity in the Las Campanas Redshift Survey

We apply Shapefinders, statistical measures of “shape constructed from two-dimensional partial Minkowski functionals, to study the degree of flamentarity in the Las Campanas Redshift Survey (LCRS). In two dimensions, three Minkowski functionals characterize the morphology of an object; these are its perimeter (L), area (S), and genus. Out of L and S a single dimensionless Shapefinder statistic, F, can be constructed (0¹ F ¹ 1). The statistic F acquires extreme values on a circle (F \ 0) and a filament (F \ 1). Using F, we quantify the extent of filamentarity in the LCRS by comparing our results with a Poisson distribution having similar geometrical properties and the same selection function as the survey. Our results unambiguously demonstrate that the LCRS displays a high degree of filamentarity in both the northern and southern Galactic sections, in general agreement with the visual appearance of the catalog. It is well known that gravitational clustering from Gaussian initial conditions gives rise to the development of non-Gaussianity, reflected in the formation of a network-like filamentary structure on supercluster scales. Consequently, the fact that the smoothed LCRS catalog shows properties consistent with those of a Gaussian random field,whereas the unsmoothed catalog demonstrates the presence of filamentarity, lends strong support to the conjecture that the large-scale clustering of galaxies is driven by gravitational instability

Conversation with Capp Yess

A conversation with Capp Yess conducted by Dakota Barr on August 22, 2016 for the Rowan County Marriage Equality and Religious Liberty Oral History Project

Acceleration of Coronal Mass Ejection Plasma in the Low Corona as Measured by the Citizen CATE Experiment

Abstract The citizen Continental-America Telescopic Eclipse (CATE) Experiment was a new type of citizen science experiment designed to capture a time sequence of white-light coronal observations during totality from 17:16 to 18:48 UT on 2017 August 21. Using identical instruments the CATE group imaged the inner corona from 1 to 2.1 RSun with 1.″43 pixels at a cadence of 2.1 s. A slow coronal mass ejection (CME) started on the SW limb of the Sun before the total eclipse began. An analysis of CATE data from 17:22 to 17:39 UT maps the spatial distribution of coronal flow velocities from about 1.2 to 2.1 RSun, and shows the CME material accelerates from about 0 to 200 km s−1 across this part of the corona. This CME is observed by LASCO C2 at 3.1–13 RSun with a constant speed of 254 km s−1. The CATE and LASCO observations are not fit by either constant acceleration nor spatially uniform velocity change, and so the CME acceleration mechanism must produce variable acceleration in this region of the corona.</jats:p