J. Einasto - Profile on Academia.edu (original) (raw)
Papers by J. Einasto
Astronomy & Astrophysics, 2007
Context. Superclusters are the largest systems in the Universe to give us information about the f... more Context. Superclusters are the largest systems in the Universe to give us information about the formation and evolution of structures in the very early Universe. Our present series of papers is devoted to the study of the morphology and internal structure of superclusters of galaxies. Aims. We study the morphology of the richest superclusters from the catalogs of superclusters of galaxies in the 2dF Galaxy Redshift Survey and compare the morphology of real superclusters with model superclusters in the Millennium Simulation. Methods. We use Minkowski functionals and shapefinders to quantify the morphology of superclusters: their sizes, shapes, and clumpiness. We generate empirical models of simple geometry to understand which morphologies correspond to the supercluster shapefinders (Appendix A). Results. Rich superclusters have elongated, filamentary shapes with high-density clumps in their core regions. The clumpiness of superclusters is determined using the fourth Minkowski functional V 3. In the K 1-K 2 shapefinder plane the morphology of superclusters is described by a curve which is characteristic of multi-branching filaments as shown by our empirical models. We found several differences between observed and model superclusters. The curves of the fourth Minkowski functional V 3 for observed and model superclusters have different shapes indicating that their structure is different. The values of V 3 for the supercluster SCL126 (the Sloan Great Wall) show that this supercluster has a very high density core which is absent in other superclusters. The values of the shapefinders H 1-H 3 and K 1 and K 2 for observed superclusters have much larger scatter than for model superclusters. The differences between the fourth Minkowski functional V 3 for the bright and faint galaxies in observed superclusters are larger than in simulated superclusters. Conclusions. Our results show how the Minkowski functionals and shapefinders can be used to describe the morphology of superclusters: their shapes, sizes and clumpiness. The shapes of observed superclusters are more diverse than the shapes of simulated superclusters. The larger scatter of the fourth Minkowski functional V 3 for the bright and faint galaxies for observed superclusters compared to simulated superclusters is an indication that the clumpiness of bright and faint galaxies in models does not reflect well the clumpiness of different galaxies in observed superclusters. Our results suggest also that the volume covered by the Millennium Simulations may be too small to properly describe the large morphological variety of superclusters.
Astronomy and Astrophysics, 2003
We study the spatial distribution of loose groups from the Las Campanas Redshift Survey, comparin... more We study the spatial distribution of loose groups from the Las Campanas Redshift Survey, comparing it with the supercluster-void network delineated by rich clusters of galaxies. We use density fields and the friends-of-friends (FoF) algorithm to identify the members of superclusters of Abell clusters among the Las Campanas loose groups. We find that systems of loose groups tend to be oriented perpendicularly to the line-of-sight, and discuss possible reasons for that. We show that loose groups in richer systems (superclusters of Abell clusters) are themselves also richer and more massive than groups in systems without Abell clusters. Our results indicate that superclusters, as high density environments, have a major role in the formation and evolution of galaxy systems.
Physical Review Letters, 1983
The authors consider nonlinear evolution of the inQationary scale-free spectrum of adiabatic dens... more The authors consider nonlinear evolution of the inQationary scale-free spectrum of adiabatic density perturbations in (1) a neutrino-dominated universe (sharp short-wavelength cutoff), and (2) an axion-, gravitino-, or photino-dominated universe (some smallscale power). In (2) galaxy formation begins long before the present (as defined by covariance function), resolving a possible problem in (1). Both models are found to be acceptable upon cluster analysis. The authors believe that a new picutre, based on (2), merits consideration.
Dark Matter in Astro- and Particle Physics, 2001
I review the observational data most relevant for large scale structure. These data determine the... more I review the observational data most relevant for large scale structure. These data determine the system of cosmological parameters: the Hubble parameter, densities of various populations of the Universe, parameters characterizing the power spectrum of matter, including the biasing parameter of galaxies relative to matter. Recent data suggest that the overall matter/energy density is approximately equal to the critical density, and most (0.6 − 0.7) of the density is in the form of cosmological term or "dark (vacuum) energy". The density of the matter is 0.3 − 0.4 (including hot and cold dark matter and luminous matter), the upper limit of the density of the hot dark matter is 0.05, all in units of the critical cosmological density.
Structure and formation of superclusters; 7, supercluster-void topology
Dark Matter in Astro- and Particle Physics, 2001
I review the observational data most relevant for large scale structure. These data determine the... more I review the observational data most relevant for large scale structure. These data determine the system of cosmological parameters: the Hubble parameter, densities of various populations of the Universe, parameters characterizing the power spectrum of matter, including the biasing parameter of galaxies relative to matter. Recent data suggest that the overall matter/energy density is approximately equal to the critical density, and most (0.6 − 0.7) of the density is in the form of cosmological term or "dark (vacuum) energy". The density of the matter is 0.3 − 0.4 (including hot and cold dark matter and luminous matter), the upper limit of the density of the hot dark matter is 0.05, all in units of the critical cosmological density.
Structure and formation of superclusters; 7, supercluster-void topology
Monthly Notices of the Royal Astronomical Society, 1997
We use rich clusters of galaxies in the Northern and Southern Galactic hemispheres up to a redshi... more We use rich clusters of galaxies in the Northern and Southern Galactic hemispheres up to a redshift z = 0.12 to determine the cluster correlation function for a separation interval ≈ 650 h −1 Mpc (h is the Hubble constant in units of 100 km s −1 Mpc −1). We show that superclusters of galaxies and voids between them form a moderately regular network. As a result the correlation function determined for clusters located in rich superclusters oscillates: it has a series of regularly spaced secondary maxima and minima. The scale of the supercluster-void network, determined from the period of oscillations, is P = 115±15 h −1 Mpc. Five periods are observed. The correlation function found for clusters in poor and medium rich superclusters is zero on large scales. The correlation functions calculated separately for the Northern and Southern Galactic hemispheres are similar. The amplitude of oscillations for clusters in the Southern hemisphere is larger by a factor of about 1.5. We investigate the influence of possible errors in the correlation function. The amplitude of oscillations for clusters in very rich superclusters is about 3 times larger than the estimated error. We argue that the oscillations in the correlation function are neither due to the double-cone shape of the observed volume of space, nor to the inaccuracy in the selection function. We compare the observed cluster correlation function with similar functions derived for popular models of structure formation, as well as for simple geometrical models of cluster distribution. We find that the production of the observed cluster correlation function in any model with a smooth transition of the power spectrum from a Harrison-Zeldovich regime with positive spectral index on long wavelengths to a negative spectral index on short wavelengths is highly unlikely. The power spectrum must have an extra peak located at the wavelength equal to the period of oscillations of the correlation function. The relative amplitude of the peak over the smooth spectrum is probably of the order of a factor of at least 1.25. These quantitative tests show that high-density regions in the Universe marked by rich clusters of galaxies are distributed more regularly than expected. Thus our present understanding of structure formation needs revision.
Brazilian Journal of Physics, 2013
The dark matter story passed through several stages on its way from a minor observational puzzle ... more The dark matter story passed through several stages on its way from a minor observational puzzle to a major challenge for theory of elementary particles. I begin the review with the description of the discovery of the mass paradox in our Galaxy and in clusters of galaxies. First hints of the problem appeared already in 1930s and later more observational arguments were brought up, but the issue of the mass
Astronomy & Astrophysics, 2003
We have studied the properties of Las Campanas Loose Groups (Tucker et al. 2000) in the neighbour... more We have studied the properties of Las Campanas Loose Groups (Tucker et al. 2000) in the neighbourhood of rich (Abell, APM and X-ray) clusters of galaxies. These loose groups show strong evidence of segregation measured in terms of the group richness and the group velocity dispersion: loose groups in the neighbourhood of a rich cluster are typically 2.5 times more massive and 1.6 times more luminous than groups on average, and these loose groups have velocity dispersions 1.3 times larger than groups on average. This is evidence that the large-scale gravitational field causing the formation of rich clusters enhances the evolution of neighbouring poor systems, a phenomenon recently established in numerical simulations of group and cluster formation.
Astronomy & Astrophysics, 2006
Aims. We use the 2dF Galaxy Redshift Survey data to compile catalogues of superclusters for the N... more Aims. We use the 2dF Galaxy Redshift Survey data to compile catalogues of superclusters for the Northern and Southern regions of the 2dFGRS, altogether 543 superclusters at redshifts 0.009 ≤ z ≤ 0.2. Methods. We analyse methods of compiling supercluster catalogues and use results of the Millennium Simulation to investigate possible selection effects and errors. We find that the most effective method is the density field method using smoothing with an Epanechnikov kernel of radius 8 h −1 Mpc. Results. We derive positions of the highest luminosity density peaks and find the most luminous cluster in the vicinity of the peak, this cluster is considered as the main cluster and its brightest galaxy the main galaxy of the supercluster. In catalogues we give equatorial coordinates and distances of superclusters as determined by positions of their main clusters. We also calculate the expected total luminosities of the superclusters.
Recently, the observed cellular nature of the large-scale structure of the Universe with its quas... more Recently, the observed cellular nature of the large-scale structure of the Universe with its quasi-regular pattern of superclusters and voids has been pointed out by several authors. In this paper, we investigate properties of the initial power spectrum which lead to prediction of structure consistent with these observations. For this purpose, we analyze the evolution of structure within four sets of 2-and 3-dimensional cosmological models, which di er in their initial power spectrum. The models include HDM and CDM models as well as double power-law models. We discuss in detail the impact of model parameters such as the large scale and small scale power and the position and height of the maxima of the power spectra on the predicted structure. Several statistical techniques were employed to compare the models with observations. They include the analysis of the distribution of voids de ned by rich and poor clusters of galaxies, voids de ned by galaxies, clusters and superclusters. In addition, the cluster correlation function is compared. We conclude that the observed regular distribution of superclusters and voids can be reproduced only if the spectrum of density uctuations has a well-de ned maximum. The wavelength of the maximum determines the scale of the structure. Small-scale uctuations determine the ne structure of the Universe. Large-scale uctuations modulate the ne structure and determine the quasi-regular structure on supercluster scales. The best agreement with observations was observed in the model with the Harrison-Zeldovich spectrum on large scales, a power index n 1:5 on small scales, and a maximum of the power spectrum at 130 h 1 Mpc. In this model the distribution of masses of clusters and superclusters, the correlation function of clusters, and the void distribution reproduce well the respective observed distributions. In models with no power on large scales all superclusters are equal in mean density, while in models with negative power index on large scales the mass distribution function of clusters is too shallow. In the HDM model (no power on small scales) the cluster-de ned voids are completely empty. CDM-models have no well-de ned maximum of the spectrum, and the cellular distribution of superclusters and voids is insu ciently developed in this case. We also investigated the dynamical evolution of the supercluster-void structure. The results show that the basic supercluster-void network is formed very early and is essentially given by initial conditions.
Clusters and groups of galaxies in 2dF (Tago+, 2006)
ABSTRACT We create a new catalogue of groups and clusters, applying the friends-to-friends method... 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).
International Astronomical Union Colloquium, 2000
Available observational data allow us to discriminate between the visible matter and the dark mat... more 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).
Symposium - International Astronomical Union, 1999
Empirical studies of the Large–Scale Structure in the nearby Universe come in two complementary m... 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.
Monthly Notices of the Royal Astronomical Society, 1993
The Spiral Structure of Our Galaxy, 1970
The density distribution and the radial velocity field in the Andromeda galaxy, M 31, have been s... more The density distribution and the radial velocity field in the Andromeda galaxy, M 31, have been studied on the basis of the 21-cm radio-line data from Jodrell Bank and Green Bank. The true density has been obtained from the observed one by solving a two-dimensional integral equation As the resolving power of the radio telescopes is too low to locate all spiral arms separately, optical data on the distribution of ionized hydrogen clouds have been also used. The mean radial velocities have been derived by solving a two-dimensional non-linear integral equation with the help of hydrogen densities, and a model radial velocity field. The inner concentrations of hydrogen form two patchy ringlike structures with mean radii 30' and 50', the outer concentrations can be represented as fragments of two leading spiral arms. The rotational velocity, derived from the radial velocity field, in the central region differs con siderably from the velocity curves obtained by earlier authors. The difference can be explained by the fact that in this region the correction for the antenna beam width is much greater than adopted by previous investigators.
Highlights of Astronomy, 1974
ESO Astrophysics Symposia, 1997
We introduce Void Hierarchy as an important property of the Large-Scale Structure in the Universe... more We introduce Void Hierarchy as an important property of the Large-Scale Structure in the Universe and demonstrate how it can be used to interpret observations. Moreover the void hierarchy constraints any realistic galaxy and structure formation scenario.
Astronomy & Astrophysics, 2007
Context. Superclusters are the largest systems in the Universe to give us information about the f... more Context. Superclusters are the largest systems in the Universe to give us information about the formation and evolution of structures in the very early Universe. Our present series of papers is devoted to the study of the morphology and internal structure of superclusters of galaxies. Aims. We study the morphology of the richest superclusters from the catalogs of superclusters of galaxies in the 2dF Galaxy Redshift Survey and compare the morphology of real superclusters with model superclusters in the Millennium Simulation. Methods. We use Minkowski functionals and shapefinders to quantify the morphology of superclusters: their sizes, shapes, and clumpiness. We generate empirical models of simple geometry to understand which morphologies correspond to the supercluster shapefinders (Appendix A). Results. Rich superclusters have elongated, filamentary shapes with high-density clumps in their core regions. The clumpiness of superclusters is determined using the fourth Minkowski functional V 3. In the K 1-K 2 shapefinder plane the morphology of superclusters is described by a curve which is characteristic of multi-branching filaments as shown by our empirical models. We found several differences between observed and model superclusters. The curves of the fourth Minkowski functional V 3 for observed and model superclusters have different shapes indicating that their structure is different. The values of V 3 for the supercluster SCL126 (the Sloan Great Wall) show that this supercluster has a very high density core which is absent in other superclusters. The values of the shapefinders H 1-H 3 and K 1 and K 2 for observed superclusters have much larger scatter than for model superclusters. The differences between the fourth Minkowski functional V 3 for the bright and faint galaxies in observed superclusters are larger than in simulated superclusters. Conclusions. Our results show how the Minkowski functionals and shapefinders can be used to describe the morphology of superclusters: their shapes, sizes and clumpiness. The shapes of observed superclusters are more diverse than the shapes of simulated superclusters. The larger scatter of the fourth Minkowski functional V 3 for the bright and faint galaxies for observed superclusters compared to simulated superclusters is an indication that the clumpiness of bright and faint galaxies in models does not reflect well the clumpiness of different galaxies in observed superclusters. Our results suggest also that the volume covered by the Millennium Simulations may be too small to properly describe the large morphological variety of superclusters.
Astronomy and Astrophysics, 2003
We study the spatial distribution of loose groups from the Las Campanas Redshift Survey, comparin... more We study the spatial distribution of loose groups from the Las Campanas Redshift Survey, comparing it with the supercluster-void network delineated by rich clusters of galaxies. We use density fields and the friends-of-friends (FoF) algorithm to identify the members of superclusters of Abell clusters among the Las Campanas loose groups. We find that systems of loose groups tend to be oriented perpendicularly to the line-of-sight, and discuss possible reasons for that. We show that loose groups in richer systems (superclusters of Abell clusters) are themselves also richer and more massive than groups in systems without Abell clusters. Our results indicate that superclusters, as high density environments, have a major role in the formation and evolution of galaxy systems.
Physical Review Letters, 1983
The authors consider nonlinear evolution of the inQationary scale-free spectrum of adiabatic dens... more The authors consider nonlinear evolution of the inQationary scale-free spectrum of adiabatic density perturbations in (1) a neutrino-dominated universe (sharp short-wavelength cutoff), and (2) an axion-, gravitino-, or photino-dominated universe (some smallscale power). In (2) galaxy formation begins long before the present (as defined by covariance function), resolving a possible problem in (1). Both models are found to be acceptable upon cluster analysis. The authors believe that a new picutre, based on (2), merits consideration.
Dark Matter in Astro- and Particle Physics, 2001
I review the observational data most relevant for large scale structure. These data determine the... more I review the observational data most relevant for large scale structure. These data determine the system of cosmological parameters: the Hubble parameter, densities of various populations of the Universe, parameters characterizing the power spectrum of matter, including the biasing parameter of galaxies relative to matter. Recent data suggest that the overall matter/energy density is approximately equal to the critical density, and most (0.6 − 0.7) of the density is in the form of cosmological term or "dark (vacuum) energy". The density of the matter is 0.3 − 0.4 (including hot and cold dark matter and luminous matter), the upper limit of the density of the hot dark matter is 0.05, all in units of the critical cosmological density.
Structure and formation of superclusters; 7, supercluster-void topology
Dark Matter in Astro- and Particle Physics, 2001
I review the observational data most relevant for large scale structure. These data determine the... more I review the observational data most relevant for large scale structure. These data determine the system of cosmological parameters: the Hubble parameter, densities of various populations of the Universe, parameters characterizing the power spectrum of matter, including the biasing parameter of galaxies relative to matter. Recent data suggest that the overall matter/energy density is approximately equal to the critical density, and most (0.6 − 0.7) of the density is in the form of cosmological term or "dark (vacuum) energy". The density of the matter is 0.3 − 0.4 (including hot and cold dark matter and luminous matter), the upper limit of the density of the hot dark matter is 0.05, all in units of the critical cosmological density.
Structure and formation of superclusters; 7, supercluster-void topology
Monthly Notices of the Royal Astronomical Society, 1997
We use rich clusters of galaxies in the Northern and Southern Galactic hemispheres up to a redshi... more We use rich clusters of galaxies in the Northern and Southern Galactic hemispheres up to a redshift z = 0.12 to determine the cluster correlation function for a separation interval ≈ 650 h −1 Mpc (h is the Hubble constant in units of 100 km s −1 Mpc −1). We show that superclusters of galaxies and voids between them form a moderately regular network. As a result the correlation function determined for clusters located in rich superclusters oscillates: it has a series of regularly spaced secondary maxima and minima. The scale of the supercluster-void network, determined from the period of oscillations, is P = 115±15 h −1 Mpc. Five periods are observed. The correlation function found for clusters in poor and medium rich superclusters is zero on large scales. The correlation functions calculated separately for the Northern and Southern Galactic hemispheres are similar. The amplitude of oscillations for clusters in the Southern hemisphere is larger by a factor of about 1.5. We investigate the influence of possible errors in the correlation function. The amplitude of oscillations for clusters in very rich superclusters is about 3 times larger than the estimated error. We argue that the oscillations in the correlation function are neither due to the double-cone shape of the observed volume of space, nor to the inaccuracy in the selection function. We compare the observed cluster correlation function with similar functions derived for popular models of structure formation, as well as for simple geometrical models of cluster distribution. We find that the production of the observed cluster correlation function in any model with a smooth transition of the power spectrum from a Harrison-Zeldovich regime with positive spectral index on long wavelengths to a negative spectral index on short wavelengths is highly unlikely. The power spectrum must have an extra peak located at the wavelength equal to the period of oscillations of the correlation function. The relative amplitude of the peak over the smooth spectrum is probably of the order of a factor of at least 1.25. These quantitative tests show that high-density regions in the Universe marked by rich clusters of galaxies are distributed more regularly than expected. Thus our present understanding of structure formation needs revision.
Brazilian Journal of Physics, 2013
The dark matter story passed through several stages on its way from a minor observational puzzle ... more The dark matter story passed through several stages on its way from a minor observational puzzle to a major challenge for theory of elementary particles. I begin the review with the description of the discovery of the mass paradox in our Galaxy and in clusters of galaxies. First hints of the problem appeared already in 1930s and later more observational arguments were brought up, but the issue of the mass
Astronomy & Astrophysics, 2003
We have studied the properties of Las Campanas Loose Groups (Tucker et al. 2000) in the neighbour... more We have studied the properties of Las Campanas Loose Groups (Tucker et al. 2000) in the neighbourhood of rich (Abell, APM and X-ray) clusters of galaxies. These loose groups show strong evidence of segregation measured in terms of the group richness and the group velocity dispersion: loose groups in the neighbourhood of a rich cluster are typically 2.5 times more massive and 1.6 times more luminous than groups on average, and these loose groups have velocity dispersions 1.3 times larger than groups on average. This is evidence that the large-scale gravitational field causing the formation of rich clusters enhances the evolution of neighbouring poor systems, a phenomenon recently established in numerical simulations of group and cluster formation.
Astronomy & Astrophysics, 2006
Aims. We use the 2dF Galaxy Redshift Survey data to compile catalogues of superclusters for the N... more Aims. We use the 2dF Galaxy Redshift Survey data to compile catalogues of superclusters for the Northern and Southern regions of the 2dFGRS, altogether 543 superclusters at redshifts 0.009 ≤ z ≤ 0.2. Methods. We analyse methods of compiling supercluster catalogues and use results of the Millennium Simulation to investigate possible selection effects and errors. We find that the most effective method is the density field method using smoothing with an Epanechnikov kernel of radius 8 h −1 Mpc. Results. We derive positions of the highest luminosity density peaks and find the most luminous cluster in the vicinity of the peak, this cluster is considered as the main cluster and its brightest galaxy the main galaxy of the supercluster. In catalogues we give equatorial coordinates and distances of superclusters as determined by positions of their main clusters. We also calculate the expected total luminosities of the superclusters.
Recently, the observed cellular nature of the large-scale structure of the Universe with its quas... more Recently, the observed cellular nature of the large-scale structure of the Universe with its quasi-regular pattern of superclusters and voids has been pointed out by several authors. In this paper, we investigate properties of the initial power spectrum which lead to prediction of structure consistent with these observations. For this purpose, we analyze the evolution of structure within four sets of 2-and 3-dimensional cosmological models, which di er in their initial power spectrum. The models include HDM and CDM models as well as double power-law models. We discuss in detail the impact of model parameters such as the large scale and small scale power and the position and height of the maxima of the power spectra on the predicted structure. Several statistical techniques were employed to compare the models with observations. They include the analysis of the distribution of voids de ned by rich and poor clusters of galaxies, voids de ned by galaxies, clusters and superclusters. In addition, the cluster correlation function is compared. We conclude that the observed regular distribution of superclusters and voids can be reproduced only if the spectrum of density uctuations has a well-de ned maximum. The wavelength of the maximum determines the scale of the structure. Small-scale uctuations determine the ne structure of the Universe. Large-scale uctuations modulate the ne structure and determine the quasi-regular structure on supercluster scales. The best agreement with observations was observed in the model with the Harrison-Zeldovich spectrum on large scales, a power index n 1:5 on small scales, and a maximum of the power spectrum at 130 h 1 Mpc. In this model the distribution of masses of clusters and superclusters, the correlation function of clusters, and the void distribution reproduce well the respective observed distributions. In models with no power on large scales all superclusters are equal in mean density, while in models with negative power index on large scales the mass distribution function of clusters is too shallow. In the HDM model (no power on small scales) the cluster-de ned voids are completely empty. CDM-models have no well-de ned maximum of the spectrum, and the cellular distribution of superclusters and voids is insu ciently developed in this case. We also investigated the dynamical evolution of the supercluster-void structure. The results show that the basic supercluster-void network is formed very early and is essentially given by initial conditions.
Clusters and groups of galaxies in 2dF (Tago+, 2006)
ABSTRACT We create a new catalogue of groups and clusters, applying the friends-to-friends method... 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).
International Astronomical Union Colloquium, 2000
Available observational data allow us to discriminate between the visible matter and the dark mat... more 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).
Symposium - International Astronomical Union, 1999
Empirical studies of the Large–Scale Structure in the nearby Universe come in two complementary m... 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.
Monthly Notices of the Royal Astronomical Society, 1993
The Spiral Structure of Our Galaxy, 1970
The density distribution and the radial velocity field in the Andromeda galaxy, M 31, have been s... more The density distribution and the radial velocity field in the Andromeda galaxy, M 31, have been studied on the basis of the 21-cm radio-line data from Jodrell Bank and Green Bank. The true density has been obtained from the observed one by solving a two-dimensional integral equation As the resolving power of the radio telescopes is too low to locate all spiral arms separately, optical data on the distribution of ionized hydrogen clouds have been also used. The mean radial velocities have been derived by solving a two-dimensional non-linear integral equation with the help of hydrogen densities, and a model radial velocity field. The inner concentrations of hydrogen form two patchy ringlike structures with mean radii 30' and 50', the outer concentrations can be represented as fragments of two leading spiral arms. The rotational velocity, derived from the radial velocity field, in the central region differs con siderably from the velocity curves obtained by earlier authors. The difference can be explained by the fact that in this region the correction for the antenna beam width is much greater than adopted by previous investigators.
Highlights of Astronomy, 1974
ESO Astrophysics Symposia, 1997
We introduce Void Hierarchy as an important property of the Large-Scale Structure in the Universe... more We introduce Void Hierarchy as an important property of the Large-Scale Structure in the Universe and demonstrate how it can be used to interpret observations. Moreover the void hierarchy constraints any realistic galaxy and structure formation scenario.