arXiv subjects

M. Einasto

Publications and source records attributed to M. Einasto.

At least 55 records · Page 3Linked to original sources

arXiv2007

The richest superclusters. II. Galaxy populations

We study the morphology of galaxy populations of the richest superclusters from the catalogue of superclusters of galaxies in the 2dF Galaxy Redshift Survey using the luminosity density distribution and Minkowski functional V3. We compare the properties of grouped and isolated galaxies in regions of different density in superclusters. We find that in high-density cores of rich superclusters there is an excess of early type, passive galaxies, among galaxies in groups and clusters, as well as among those which do not belong to groups, while in lower density outer regions there are more blue, star-forming galaxies both in groups and among those galaxies which do not belong to groups. This also shows that the galaxy content of groups depends on the environment where the groups reside in. The density distributions and the behaviour of the Minkowski functional V3 for different superclusters show that substructures in superclusters as traced by different populations of galaxies are very different. Our results show that both local (group/cluster) and global (supercluster) environments are important in forming galaxy morphologies and star formation activity. The presence of a high density core with X-ray clusters and a relatively small fraction of star-forming galaxies in the supercluster SCL126 may be an indication that this supercluster has started its evolution earlier than the supercluster SCL9.

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arXiv2007

The richest superclusters. I. Morphology

We study the morphology of the richest superclusters from the catalogues of superclusters of galaxies in the 2dF Galaxy Redshift Survey and compare the morphology of real superclusters with model superclusters in the Millennium Simulation. 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. We show that 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 to multi-branching filaments. We also find that the differences between the fourth Minkowski functional $V_3$ for the bright and faint galaxies in observed superclusters are larger than in simulated superclusters.

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arXiv2006

Subhaloes in $Λ$CDM cosmological simulations: I. Masses and abundances

If the concordance $Λ$CDM model is a true description of the universe, it should also properly predict the properties and structure of dark matter haloes, where galaxies are born. Using N-body simulations with a broad scale of mass and spatial resolution, we study the structure of dark matter haloes, the distribution of masses and the spatial distribution of subhaloes within the main haloes. We carry out three $Λ$CDM simulations with different resolutions using the AMIGA code. Dark matter haloes are identified using an algorithm that is based on the adaptive grid structure of the simulation code. The haloes we find encompass the mass scales from $10^8\mathrm{M}_{\sun}$ to $10^{15}\mathrm{M}_{\sun}$. We find that if we have to study the halo structure (search for subhaloes), the haloes have to contain at least $10^4$ particles. For such haloes, where we can resolve substructure, we determined the subhalo mass function and found that it is close to a power law with the slope -0.9 (at present time), consistent with previous studies. This slope depends slightly on the redshift and it is approximately the same for main haloes. The subhalo mass fraction ($M_{\s subH}/M_{\s MH}$) is between 0.08 and 0.2, increasing slightly with redshift and with the mass of the main halo. Its distribution is approximated using the Weibull distribution at different epochs. The mean values of subhalo mass are independent of the main halo mass. The spatial density of subhaloes, scaled to the virial radius of the main halo ($r_{\s vir}$), is independent of redshift and follows the $r^{1/3}$ rule.

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arXiv2006

Superclusters of galaxies in the 2dF redshift survey. III. The properties of galaxies in superclusters

We use catalogues of superclusters of galaxies from the 2dF Galaxy Redshift Survey to study the properties of galaxies in superclusters. We compare the properties of galaxies in high and low density regions of rich superclusters, in poor superclusters and in the field, as well as in groups, and of isolated galaxies in superclusters of various richness. We show that in rich superclusters the values of the luminosity density smoothed on a scale of 8 \Mpc are higher than in poor superclusters: the median density in rich superclusters is $δ\approx 7.5$, in poor superclusters $δ\approx 6.0$. Rich superclusters contain high density cores with densities $δ> 10$ while in poor superclusters such high density cores are absent. The properties of galaxies in rich and poor superclusters and in the field are different: the fraction of early type, passive galaxies in rich superclusters is slightly larger than in poor superclusters, and is the smallest among the field galaxies. Most importantly, in high density cores of rich superclusters ($δ> 10$) there is an excess of early type, passive galaxies in groups and clusters, as well as among those which do not belong to groups or clusters. The main galaxies of superclusters have a rather limited range of absolute magnitudes. The main galaxies of rich superclusters have larger luminosities than those of poor superclusters and of groups in the field. Our results show that both the local (group/cluster) environments and global (supercluster) environments influence galaxy morphologies and their star formation activity.

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arXiv2006

Luminous superclusters: remnants from inflation

We derive the luminosity and multiplicity functions of superclusters compiled for the 2dF Galaxy Redshift Survey, the Sloan Digital Sky Survey (Data Release 4), and for three samples of simulated superclusters. We find for all supercluster samples Density Field (DF) clusters, which represent high-density peaks of the class of Abell clusters, and use median luminosities/masses of richness class 1 DF-clusters to calculate relative luminosity/mass functions. We show that the fraction of very luminous (massive) superclusters in real samples is more than tenfolds greater than in simulated samples. Superclusters are generated by large-scale density perturbations which evolve very slowly. The absence of very luminous superclusters in simulations can be explained either by non-proper treatment of large-scale perturbations, or by some yet unknown processes in the very early Universe.

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arXiv2006

Superclusters of galaxies from the 2dF redshift survey. II. Comparison with simulations

We investigate properties of superclusters of galaxies found on the basis of the 2dF Galaxy Redshift Survey, and compare them with properties of superclusters from the Millennium Simulation. We study the dependence of various characteristics of superclusters on their distance from the observer, on their total luminosity, and on their multiplicity. The multiplicity is defined by the number of Density Field (DF) clusters in superclusters. Using the multiplicity we divide superclusters into four richness classes: poor, medium, rich and extremely rich. We show that superclusters are asymmetrical and have multi-branching filamentary structure, with the degree of asymmetry and filamentarity being higher for the more luminous and richer superclusters. The comparison of real superclusters with Millennium superclusters shows that most properties of simulated superclusters agree very well with real data, the main differences being in the luminosity and multiplicity distributions.

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arXiv2006

Superclusters of galaxies from the 2dF redshift survey. I. The catalogue

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. 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 Mpc/h. 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.

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arXiv2005

Clusters and groups of galaxies in the 2dF galaxy redshift survey

We create a new catalogue of groups and clusters for the 2dF GRS final release sample. We show that the variable linking length friends-of-friends (FoF) algorithms used so far yield groups with sizes that grow systematically with distance from the observer, but FoF algorithms with a constant linking length are free from this fault. We apply the FoF algorithm with a constant linking length for the 2dF GRS, compare for each group its potential and kinetic energies and remove galaxies with excess random velocities. Our sample contains 7657 groups in the Northern part, and 10058 groups in the Southern part of the 2dF survey with membership Ng >= 2. We analyze selection effects of the catalogue and compare our catalogue of groups with other recently published catalogues based on the 2dF GRS. We also estimate the total luminosities of our groups, correcting for group members fainter than the observational limit of the survey. The cluster catalogues are available at our web-site (http://www.aai.ee/~maret/2dfgr.html)

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arXiv2004

Environmental Enhancement of DM Haloes

We study the properties of dark matter haloes of a LCDM model in different environments. Using the distance of the 5th nearest neighbour as an environmental density indicator, we show that haloes in a high density environment are more massive, richer, have larger radii and larger velocity dispersions than haloes in a low density environment. Haloes in high density regions move with larger velocities, and are more spherical than haloes in low density regions. In addition, low mass haloes in the vicinity of the most massive haloes are themselves more massive, larger, and have larger rms velocities and larger 3D velocities than low mass haloes far from massive haloes. The velocities of low mass haloes near massive haloes increase with the parent halo mass. Our results are in agreement with recent findings about environmental effects for groups and clusters of galaxies from deep (SDSS and LCRS) surveys.

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arXiv2004

Toward Understanding Environmental Effects in SDSS Clusters

We find clusters and superclusters of galaxies using the Data Release 1 of the Sloan Digital Sky Survey. We determine the luminosity function of clusters and find that clusters in a high-density environment have a luminosity a factor of ~5 higher than in a low-density environment. We also study clusters and superclusters in numerical simulations. Simulated clusters in a high-density environment are also more massive than those in a low-density environment. Comparison of the density distribution at various epochs in simulations shows that in large low-density regions (voids) dynamical evolution is very slow and stops at an early epoch. In contrast, in large regions of higher density (superclusters) dynamical evolution starts early and continues until the present; here particles cluster early, and by merging of smaller groups very rich systems of galaxies form.

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arXiv2004

Clusters and Superclusters in the Sloan Survey

We find clusters and superclusters of galaxies using the Data Release 1 of the Sloan Digital Sky Survey. Density fields with smoothing lengthst of 10 and 0.8 Mpc/h are calculated. We found that galaxies and clusters in a high-density environment have luminosities that are five to ten times higher than in a low-density environment. Numerical simulations show that in underdense regions most particles form a rarefied population of pregalactic matter whereas in overdense regions most particles form a clustered population in rich clusters. Simulations show also that very massive superclusters are great attractors and have small bulk motions.

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arXiv2004

Redshifts and Distribution of ACO Clusters of Galaxies

The June 2004 version of our compilation of measured redshifts for clusters in the Abell-ACO catalogue lists redshifts for 3715 clusters/subclusters in 3033 distinct (2396 A- and 637 S-) clusters, 67% of these with N_z>=3 galaxies measured. We provide velocity dispersions (sigma_V) for 1875 (sub)clusters towards 1353 unique ACO clusters. The median sigma_V is 650 km/s for A-(sub)clusters and 575 km/s for S-(sub)clusters, and sigma_V clearly increases with both, N_z and richness, and also, somewhat surprising, with later Bautz-Morgan type of the clusters. We show examples of supercluster properties based on these data.

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arXiv2003

Las Campanas Loose Groups in the Supercluster-Void Network

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 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.

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arXiv2003

Clusters and Superclusters in the Las Campanas Redshift Survey

Two-dimensional high-resolution density field of galaxies of the Las Campanas Redshift Survey (LCRS) with a smoothing length 0.8 Mpc/h is used to extract clusters and groups of galaxies, and a low-resolution field with a smoothing length 10 Mpc/h to find superclusters of galaxies. Properties of these density field (DF) clusters and superclusters are studied and compared with the properties of Abell clusters and superclusters, and LCRS loose groups. We calculate the DF-cluster luminosity function, and show that most luminous clusters in high-density environments are about ten times brighter than most luminous clusters in low-density environments. We present a catalogue of DF-superclusters and show that superclusters that contain Abell clusters are richer and more luminous than superclusters without Abell clusters. A pdf file of the paper with high-resolution figures is available in Tartu Observatory web-site (http://www.aai.ee/~maret/cosmoweb.html)

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arXiv2002

Luminosity function and density field of the Sloan and Las Campanas Redshift Survey

The luminosity function of galaxies of the Early Data Release of the Sloan Digital Sky Survey (SDSS) and the Las Campanas Redshift Survey (LCRS) is calculated. The luminosity function depends on redshift, density of the environment and is different for the Norther and Southern slice of SDSS. Luminosity functions is used to derive the number and luminosity density fields of galaxies of the SDSS and LCRS surveys with a grid size of 1 h^{-1} Mpc for flat cosmological models with Ω_m=0.3 and Ω_Λ=0.7. We find that the luminosity function depends on the density of the environment: in high-density regions brightest galaxies are more luminous than in low-density regions by a factor up to 5.

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arXiv2002

Clusters and Superclusters in the Sloan Digital Sky Survey

Two-dimensional high-resolution density field of galaxies of the Early Data Release of the Sloan Digital Sky Survey with a smoothing lengths 0.8 h^{-1} Mpc is applied to extract clusters of galaxies, and a low-resolution field with smoothing lengths 10^{-1} Mpc to extract superclusters of galaxies. We compare properties of density field clusters and superclusters with Abell clusters, and superclusters found on the basis of Abell clusters. We found that clusters in high-density environment have a luminosity a factor of about 5 higher than in low-density environment. There exists a large anisotropy between the SDSS Northern and Southern sample in the properties of clusters and superclusters: most luminous clusters and superclusters in the Northern sample are a factor of 2 more luminous than the respective systems in the Southern sample.

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arXiv2002

Environmental Enhancement of Loose Groups around Rich Clusters of Galaxies

We have studied the properties of Las Campanas Loose Groups 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 havevelocity 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.

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arXiv2002

The mass function of the Las Campanas loose groups of galaxies

We have determined the mass function of loose groups of galaxies in the Las Campanas Redshift Survey. Loose groups of galaxies in the LCRS range in mass from $M \sim 10^{12} {\rm M}_{\sun}$ to $10^{15} {\rm M}_{\sun}$. We find that the sample is almost complete for masses in the interval $5\cdot 10^{13}-8\cdot 10^{14} {\rm M}_{\sun}$. Comparison of the observed mass function with theoretical mass functions obtained from N-body simulations shows good agreement with a CDM model with the parameters $Ω_m = 0.3$, $Ω_Λ = 0.7$ and the amplitude of perturbations about $σ_8=0.78-0.87$. For smaller masses the mass function of LCRS loose groups flattens out, differing considerably from the group mass function found by Girardi and Giuricin (2000) and from mass functions obtained by numerical simulations.

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