Collapse,Connectivity, and Galaxy Populations in Supercluster Cocoons: the Case of A2142

Astronomy Reports - The largest galaxy systems in the cosmic web are superclusters, overdensity regions of galaxies, groups, clusters, and filaments. Low-density regions around superclusters are...     

Clusters and groups of galaxies in the 2dF galaxy redshift survey: A new catalogue

We create a new catalogue of groups and clusters, applying the friends‐of‐friends method to the 2dF GRS final release. We investigate various selection effects due to the use of a magnitude limited sample. For this purpose we follow the changes in group sizes and mean galaxy number densities within groups when shifting nearby observed groups to larger distances. We study the distribution of sizes of dark matter haloes in N ‐body simulations and compare properties of these haloes and the 2dF groups. We show that at large distances from the observer luminous and intrinsically greater groups dominate, but in these groups only very bright members are seen, which form compact cores of the groups. These two effects almost cancel each other, so that the mean sizes and densities of groups do not change considerably with distance. Our final sample contains 10750 groups in the Northern part, and 14465 groups in the Southern part of the 2dF survey with membership N _gal ≥ 2. We estimate the total luminosities of our groups, correcting for group members fainter than the observational limit of the survey. The cluster catalogue is available at our web‐site ( http://www.aai.ee/∼maret/2dfgr.html ). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Deep slices and the Supercluster-Void Network

We compare the properties of superclusters of Abell clusters with those of superclusters of loose groups from the Las Campanas Redshift Survey. We show that supercluster intersections with the LCRS slices coincide with the high-density regions of the galaxy distribution. The orientation of superclusters in respect of line-of-sight is nearly random, with a slight excess of systems oriented perpendicularly to the line of sight.     

The role of diffuse matter in galactic coronas

An upper limit to the gas content in the coronas of giant galaxiesM _gas<0.04M _cor has been calculated on the basis of observational data on the emission of clusters of galaxies in different wavelength ranges. An analysis of companion galaxies has revealed a correlation of their morphological types with the distances to central giant galaxies. A gasodynamical interpretation of this regularity is suggested and a possible picture of the evolution of the galactic coronas is presented.     

Shallow sediment transport flow computation using time-varying sediment adaptation length

Based on the common approach,the adaptation length in sediment transport is normally estimated astemporally independent.However,this approach might not be theoretically justified as the process of reaching the sediment transport equilibrium stage is affected by the flow conditions in time,especially for fast moving flows,such as scour-hole developing flows.In this study,the two-dimensional（2D） shallow water formulation together with a sediment continuity-concentration（SCC） model were applied to flow with mobile sediment boundary.A timevarying approach was proposed to determine the sediment transport adaptation length to simulate the sediment erosion-deposition rate.The proposed computational model was based on the Finite Volume（FV） method.The Monotone Upwind Scheme of Conservative Laws（MUSCL）-Hancock scheme was used with the Harten Lax van Leer-contact（HLLC） approximate Riemann solver to discretize the FV model.In the flow applications of this paper,a highly discontinuous dam-break,fast sediment transport flow was used to calibrate the proposed timevarying sediment adaptation length model.Then the calibrated model was further applied to two separate experimental sediment transport flow applications documented in the literature,i.e.a highly concentrated sediment transport flow in a wide alluvial channel and a sediment aggradation flow.Good agreement with the experimental data were obtained with the proposed model simulations.The tests prove that the proposed model,which was calibrated by the discontinuous dam-break bed scouring flow,also performed well to represent rapid bed change and steady sediment mobility conditions.     

Light curves of gas-eclipsed binary systems

Light curves have been calculated for the model of a binary system consisting of two spherical components, imbedded in a common spherically-symmetric, isotropically-scattering envelope with radially-varying opacity. The periodically-varying screening of stellar radiation by the envelope gives rise to regular light changes, which are similar to stellar eclipses during a superior conjunction of the components and in maxima resemble the light changes due to the reflection effect for Algol-type binaries, whereas for systems with nearly equal luminosities of the components they match light variations, caused by the gravitational distortions of stellar figures.It is shown that the light changes in AO Cas can be interpreted in terms of our model and we propose to call binaries of that type gas-eclipsed variables. The observed light curves RY Gem, RS CVn, VW Cep are compared with the model curves. It is indicated that the light curve of the Algol-type system RY Gem can be interpreted in the framework of the adopted model, provided that stellar eclipses are accompanied by the screening effect of the envelope.Asymmetry, local fluctuations, different widths of minima, and some other peculiarities of the observed light curves are discussed within the context of our model. It can be regarded as a certain optical counterpart of the Roche model, since the isophotes of the envelope resemble the Roche equipotentials in their behaviour.     

Biasing Phenomenon

Astronomy Reports - We study biasing as a physical phenomenon by analyzing power spectra (PS) and correlation functions (CF) of simulated galaxy samples and dark matter (DM) samples. We apply an...