J. Einasto
University of Tartu, Cosmology, Emeritus
- I am a researcher interested in Universeedit
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Research Interests: Physics, Observational Cosmology, Galaxy Clusters, Geometric model, Oscillations, and 12 moreSpectrum, Southern Hemisphere, Power Spectrum, large scale structure of the Universe, High Density Concrete, General Relativity and Cosmology, Indexation, Large Scale, Similarity Function, Steel Structure Formation, Correlation function, and High density
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Research Interests: Physics, Galaxy Clusters, Dust (Astronomy & Astrophysics), Astrophysics, Statistical Techniques in Spatial Analysis, and 13 morePower Law, Dimensional, Fine Structure Constant, Spectrum, Power Spectrum, large scale structure of the Universe, Indexation, Large Scale, Initial Condition, Astronomy and Astrophysics, Correlation function, Statistical techniques, and Distribution Function
ABSTRACT We create a new catalogue of groups and clusters, applying the friends-to-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... more
ABSTRACT We create a new catalogue of groups and clusters, applying the friends-to-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 the 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. (6 data files).
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Available observational data allow us to discriminate between the visible matter and the dark matter in M 31 and thus to determine the most important parameters of the dark halo (the mass, the radius and the outer extent).
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Empirical studies of the Large–Scale Structure in the nearby Universe come in two complementary modes, namely the investigation of either the distribution of luminous matter or voids: (i) The description of the galaxy and cluster... more
Empirical studies of the Large–Scale Structure in the nearby Universe come in two complementary modes, namely the investigation of either the distribution of luminous matter or voids: (i) The description of the galaxy and cluster distribution employs correlation functions, clustering analysis, topological methods, et cetera. (ii) The investigation of the empty regions between systems of galaxies uses void probability functions, mean diameters of voids, the compilation of void catalogues, and so forth.
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This report is intended to provide references to works done during the triennium 1988–1990 (including references for 1987) in the general field of galactic structure. “Astronomy and Astrophysics Abstracts” provides an exhaustive list of... more
This report is intended to provide references to works done during the triennium 1988–1990 (including references for 1987) in the general field of galactic structure. “Astronomy and Astrophysics Abstracts” provides an exhaustive list of works related to galactic structure and dynamics and it is not the aim of this report to duplicate this already existing service. Only a selection of works, illustrating some trends and highlights (a subjective view!), are described here and will certainly allow a comprehensive view of the broad domain of galactic research.
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We study subhalo populations surrounding massive dark matter haloes by using three AMIGA simulations each having different mass and spatial resolutions. Our analysis shows that the slope of the subhalo mass function has a value 0.9, which... more
We study subhalo populations surrounding massive dark matter haloes by using three AMIGA simulations each having different mass and spatial resolutions. Our analysis shows that the slope of the subhalo mass function has a value 0.9, which agrees with previous studies. The dependence of mass functions on redshift is the same for subhaloes and main haloes. In all simulations, combined subhalo masses are about 0.1-0.2 of main halo masses and this mass fraction increases slightly with redshift and the mass of the main halo. The distribution of mass fractions for subhaloes is close to Gaussian at z = 0 and differs slightly at earlier epochs. Spatial distribution of subhaloes as measured in units of virial radius Rvir of the main halo does not depend on redshift and follows r1/3 rule. Spatial distribution of all haloes surrounding main haloes continues up to 3 times Rvir with equal slope but lower amplitude. Beyond 16 times Rvir, the average distribution of haloes becomes uniform.
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Context. According to the modern cosmological paradigm cosmic voids form in low density regions between filaments of galaxies and superclusters. Aims. Our goal is to see how density waves of different scale combine to form voids between... more
Context. According to the modern cosmological paradigm cosmic voids form in low density regions between filaments of galaxies and superclusters. Aims. Our goal is to see how density waves of different scale combine to form voids between galaxy systems of various scale. Methods. We perform numerical simulations of structure formation in cubes of size 100, 256, and 512 h −1 Mpc, with resolutions 256 3 and 512 3 particles and cells. To understand the role of density pertu rbations of various scale we cut power spectra at scales from 8 to 128 h −1 Mpc, using in all series identical initial random realisati ons. Results. We find that small haloes and short filaments form all over the s imulation box, if perturbations only up to scale 8 h −1 Mpc are present. We call density waves of scale≥ 64 h −1 Mpc as large, waves of scale≃ 32 h −1 Mpc as medium scale, and waves of scale ≃ 8 h −1 Mpc as small scale, within a factor of 2. Voids form in regions where medium- and large-scale density perturbations combine in negative parts of waves due to the synchronisation of phases of medium- and large-scale density perturbations. In voids the growth of potential haloes (formed in the absence of large-scale perturbations) is suppressed by the combined negative sections of mediumand large-scale density perturbations, so that their densi ties are less than the mean density, and thus during the evolution their densities decrease. Conclusions. The void phenomenon requires an extended spectrum of primordial density perturbations and is due to the action of two processes: the synchronisation of density perturbations of medium and large scales, and the suppression of galaxy formation in low-density regions by combined action of negative sections of medium- and large-scale density perturbations.
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The large-scale structure of the Universe as delineated by clusters of galaxies is dominated by a network of alternate superclusters and voids - or cells, superclusters forming cell walls and voids cell interiors. The cellular structure... more
The large-scale structure of the Universe as delineated by clusters of galaxies is dominated by a network of alternate superclusters and voids - or cells, superclusters forming cell walls and voids cell interiors. The cellular structure is surprisingly regular, the mutual distance between high-density peaks of neighbouring superclusters is dt ≈ 130 h-1Mpc. Voids defined by rich clusters of galaxies are not empty but contain filaments of galaxies and systems of galaxies of lower richness. Bright galaxies inside cluster defined voids are dominantly spirals whereas bright galaxies in void walls are dominantly ellipticals. The whole picture shows the presence of a hierarchy of systems of galaxies and voids. The cellular structure with alternate high- and low-density regions is expected for a two-power law density spectrum with a maximum near the observed scale dt.
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We have developed a parameter-independent method to detect local maxima of the two-point correlation function. By applying it to two samples of rich Abell clusters of galaxies with redshift limits z<0.08 and z<0.12 we detect three... more
We have developed a parameter-independent method to detect local maxima of the two-point correlation function. By applying it to two samples of rich Abell clusters of galaxies with redshift limits z<0.08 and z<0.12 we detect three maxima centered at 150 Mpc, 300 Mpc and 430 Mpc with confidence levels 80% and higher. This sequence of fluctuations has an average interval of 140 Mpc, that can be explained by a power spectrum with a distinct peak at k=0.048+-0.005/Mpc.
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