Search

The cosmological missing baryons at z<1 most likely hide in the hot (T$\gtrsim10^{5.5}$ K) phase of the Warm Hot Intergalactic Medium (WHIM). While the hot WHIM is hard to detect due to its high ionisation level, the warm (T$\lesssim10^{5.5}$ K) phase of the WHIM has been very robustly detected in the FUV band. We adopted the assumption that the hot and warm WHIM phases are co-located and thus used the FUV-detected warm WHIM as a tracer for the cosmologically interesting hot WHIM. We utilised the assumption by performing an X-ray follow-up in the sight line of a blazar PKS 2155-304 at the redshifts where previous FUV measurements of OVI, SiIV and BLA absorption have indicated the existence of the warm WHIM. We looked for the OVII He$\alpha$ and OVIII Ly$\alpha$ absorption lines, the most likely hot WHIM tracers. Despite of the very large exposure time ($\approx$ 1 Ms), the XMM-Newton/RGS1 data yielded no significant detection which corresponds to upper limits of $\log{N({\rm OVII})({\rm cm}^{-2}))} \le 14.5-15.2$ and $\log{N({\rm OVIII})({\rm cm}^{-2}))} \le 14.9-15.2$. An analysis of LETG/HRC data yielded consistent results. However, the LETG/ACIS data yielded a detection of an absorption line - like feature at $\lambda \approx$ 20 \AA\ at simple one parameter uncertainty - based confidence level of 3.7 $\sigma$, consistently with several earlier LETG/ACIS reports. Given the high statistical quality of the RGS1 data, the possibility of RGS1 accidentally missing the true line at $\lambda \sim$ 20 \AA\ is very low, 0.006%. Neglecting this, the LETG/ACIS detection can be interpreted as Ly$\alpha$ transition of OVIII at one of the redshifts (z$\approx$ 0.054) of FUV-detected warm WHIM. Given the very convincing X-ray spectral evidence for and against the existence of the $\lambda \sim$ 20 \AA\ feature, we cannot conclude whether or not it is a true astrophysical absorption line., Comment: Accepted for A&A

We study the alignment of galaxies relative to their local environment in SDSS-DR8 and, using these data, we discuss evolution scenarios for different types of galaxies. We defined a vector field of the direction of anisotropy of the local environment of galaxies. We summed the unit direction vectors of all close neighbours of a given galaxy in a particular way to estimate this field. We found the alignment angles between the spin axes of disc galaxies, or the minor axes of elliptical galaxies, and the direction of anisotropy. The distributions of cosines of these angles are compared to the random distributions to analyse the alignment of galaxies. Sab galaxies show perpendicular alignment relative to the direction of anisotropy in a sparse environment, for single galaxies and galaxies of low luminosity. Most of the parallel alignment of Scd galaxies comes from dense regions, from 2...3 member groups and from galaxies with low luminosity. The perpendicular alignment of S0 galaxies does not depend strongly on environmental density nor luminosity; it is detected for single and 2...3 member group galaxies, and for main galaxies of 4...10 member groups. The perpendicular alignment of elliptical galaxies is clearly detected for single galaxies and for members of < 11 member groups; the alignment increases with environmental density and luminosity. We confirm the existence of fossil tidally induced alignment of Sab galaxies at low z. The alignment of Scd galaxies can be explained via the infall of matter to filaments. S0 galaxies may have encountered relatively massive mergers along the direction of anisotropy. Major mergers along this direction can explain the alignment of elliptical galaxies. Less massive, but repeated mergers are possibly responsible for the formation of elliptical galaxies in sparser areas and for less luminous elliptical galaxies., Comment: 15 pages, 15 figures, accepted for publication in A&A

The cosmic web is a highly complex geometrical pattern, with galaxy clusters at the intersection of filaments and filaments at the intersection of walls. Identifying and describing the filamentary network is not a trivial task due to the overwhelming complexity of the structure, its connectivity and the intrinsic hierarchical nature. To detect and quantify galactic filaments we use the Bisous model, which is a marked point process built to model multi-dimensional patterns. The Bisous filament finder works directly with the galaxy distribution data and the model intrinsically takes into account the connectivity of the filamentary network. The Bisous model generates the visit map (the probability to find a filament at a given point) together with the filament orientation field. Using these two fields, we can extract filament spines from the data. Together with this paper we publish the computer code for the Bisous model that is made available in GitHub. The Bisous filament finder has been successfully used in several cosmological applications and further development of the model will allow to detect the filamentary network also in photometric redshift surveys, using the full redshift posterior. We also want to encourage the astro-statistical community to use the model and to connect it with all other existing methods for filamentary pattern detection and characterisation., Comment: 12 pages, 6 figures, accepted by Astronomy and Computing

Superclusters are the largest relatively isolated systems in the cosmic web. Using the SDSS BOSS survey we search for the largest superclusters in the redshift range $0.43

This paper describes several applications in astronomy and cosmology that are addressed using probabilistic modelling and statistical inference.

We propose a new approach to the missing baryons problem. Building on the common assumption that the missing baryons are in the form of the Warm Hot Intergalactic Medium (WHIM), we further assumed here that the galaxy luminosity density can be used as a tracer of the WHIM. The latter assumption is supported by our finding of a significant correlation between the WHIM density and the galaxy luminosity density in the hydrodynamical simulations of Cui et al. (2012). We further found that the fraction of the gas mass in the WHIM phase is substantially (by a factor of $\sim$1.6) higher within the large scale galactic filaments, i.e. $\sim$70\%, compared to the average in the full simulation volume of $\sim$0.1\,Gpc$^3$. The relation between the WHIM overdensity and the galaxy luminosity overdensity within the galactic filaments is consistent with linear: $\delta_{\rm whim}\,=\,0.7\,\pm\,0.1\,\times\,\delta_\mathrm{LD}^{0.9 \pm 0.2}$. We applied our procedure to the line of sight to the blazar H2356-309 and found evidence for the WHIM in correspondence of the Sculptor Wall (z $\sim$0.03 and $\log{N_H}$ = $19.9^{+0.1}_{-0.3}$) and Pisces-Cetus superclusters (z $\sim$0.06 and $\log{N_H}$ = $19.7^{+0.2}_{-0.3}$), in agreement with the redshifts and column densities of the X-ray absorbers identified and studied by Fang et al. (2010) and Zappacosta et al. (2010). This agreement indicates that the galaxy luminosity density and galactic filaments are reliable signposts for the WHIM and that our method is robust in estimating the WHIM density. The signal that we detected cannot originate from the halos of the nearby galaxies since they cannot account for the large WHIM column densities that our method and X-ray analysis consistently find in the Sculptor Wall and Pisces-Cetus superclusters., Comment: Accepted for Astronomy & Astrophysics

Signatures of the processes in the early Universe are imprinted in the cosmic web. Some of them may define shell-like structures characterised by typical scales. We search for shell-like structures in the distribution of nearby rich clusters of galaxies drawn from the SDSS DR8. We calculate the distance distributions between rich clusters of galaxies, and groups and clusters of various richness, look for the maxima in the distance distributions, and select candidates of shell-like structures. We analyse the space distribution of groups and clusters forming shell walls. We find six possible candidates of shell-like structures, in which galaxy clusters have maxima in the distance distribution to other galaxy groups and clusters at the distance of about 120 Mpc/h. The rich galaxy cluster A1795, the central cluster of the Bootes supercluster, has the highest maximum in the distance distribution of other groups and clusters around them at the distance of about 120 Mpc/h among our rich cluster sample, and another maximum at the distance of about 240 Mpc/h. The structures of galaxy systems causing the maxima at 120 Mpc/h form an almost complete shell of galaxy groups, clusters and superclusters. The richest systems in the nearby universe, the Sloan Great Wall, the Corona Borealis supercluster and the Ursa Major supercluster are among them. The probability that we obtain maxima like this from random distributions is lower than 0.001. Our results confirm that shell-like structures can be found in the distribution of nearby galaxies and their systems. The radii of the possible shells are larger than expected for a BAO shell (approximately 109 Mpc/h versus approximately 120 Mpc/h), and they are determined by very rich galaxy clusters and superclusters with high density contrast while BAO shells are barely seen in the galaxy distribution. We discuss possible consequences of these differences., Comment: Comments: 9 pages, 10 figures, Astronomy and Astrophysics, in press

We have developed a new method to approach the missing baryons problem. We assume that the missing baryons reside in a form of Warm Hot Intergalactic Medium, i.e. the WHIM. Our method consists of (a) detecting the coherent large scale structure in the spatial distribution of galaxies that traces the Cosmic Web and that in hydrodynamical simulations is associated to the WHIM, (b) map its luminosity into a galaxy luminosity density field, (c) use numerical simulations to relate the luminosity density to the density of the WHIM, (d) apply this relation to real data to trace the WHIM using the observed galaxy luminosities in the Sloan Digital Sky Survey and 2dF redshift surveys. In our application we find evidence for the WHIM along the line of sight to the Sculptor Wall, at redshifts consistent with the recently reported X-ray absorption line detections. Our indirect WHIM detection technique complements the standard method based on the detection of characteristic X-ray absorption lines, showing that the galaxy luminosity density is a reliable signpost for the WHIM. For this reason, our method could be applied to current galaxy surveys to optimise the observational strategies for detecting and studying the WHIM and its properties. Our estimates of the WHIM hydrogen column density in Sculptor agree with those obtained via the X-ray analysis. Due to the additional column density estimate, our method has potential for improving the constrains of the physical parameters of the WHIM as derived with X-ray absorption, and thus for improving the understanding of the missing baryons problem., Comment: Proceedings of the IAU308 Symposium "The Zeldovic Universe", Cambridge University Press, submitted

Context. Galaxies in the Universe form chains (filaments) that connect groups and clusters of galaxies. The filamentary network includes nearly half of the galaxies and is visually the most striking feature in cosmological maps. Aims. We study the distribution of galaxies along the filamentary network, trying to find specific patterns and regularities. Methods. Galaxy filaments are defined by the Bisous model, a marked point process with interactions. We use the two-point correlation function and the Rayleigh Z-squared statistic to study how galaxies and galaxy groups are distributed along the filaments. Results. We show that galaxies and groups are not uniformly distributed along filaments, but tend to form a regular pattern. The characteristic length of the pattern is around 7 Mpc/h. A slightly smaller characteristic length 4 Mpc/h can also be found, using the Z-squared statistic. Conclusions. We find that galaxy filaments in the Universe are like pearl necklaces, where the pearls are galaxy groups distributed more or less regularly along the filaments. We propose that this well defined characteristic scale could be used to test various cosmological models and to probe environmental effects on the formation and evolution of galaxies., Comment: 8 pages, 9 figures, 1 table, accepted for publication in A&A

We provide flux-limited and volume-limited galaxy group and cluster catalogues, based on the spectroscopic sample of the SDSS data release 10 galaxies. We used a modified friends-of-friends (FoF) method with a variable linking length in the transverse and radial directions to identify as many realistic groups as possible. The flux-limited catalogue incorporates galaxies down to m_r = 17.77 mag. It includes 588193 galaxies and 82458 groups. The volume-limited catalogues are complete for absolute magnitudes down to M_r = -18.0, -18.5, -19.0, -19.5, -20.0, -20.5, and -21.0; the completeness is achieved within different spatial volumes, respectively. Our analysis shows that flux-limited and volume-limited group samples are well compatible to each other, especially for the larger groups/clusters. Dynamical mass estimates, based on radial velocity dispersions and group extent in the sky, are added to the extracted groups. The catalogues can be accessed via http://cosmodb.to.ee and the Strasbourg Astronomical Data Center (CDS)., Comment: 16 pages, 18 figures, 2 tables, accepted for publication in A&A

The Millennium N-body simulation and the Sloan Digital Sky Survey seventh data release (SDSS DR7) galaxy and galaxy group catalogues are compared to study the properties of galaxy groups and the distribution of galaxies in groups. We construct mock galaxy group catalogues for a Millennium semi-analytical galaxy catalogue by using the same friends-of-friends method, which was used by Tago et al to analyse the SDSS data. We analyse in detail the group luminosities, group richnesses, virial radii, sizes of groups and their rms velocities for four volume-limited samples from observations and simulations. Our results show that the spatial densities of groups agree within one order of magnitude in all samples with a rather good agreement between the mock catalogues and observations. All group property distributions have similar shapes and amplitudes for richer groups. For galaxy pairs and small groups, the group properties for observations and simulations are clearly different. In addition, the spatial distribution of galaxies in small groups is different: at the outskirts of the groups the galaxy number distributions do not agree, although the agreement is relatively good in the inner regions. Differences in the distributions are mainly due to the observational limitations in the SDSS sample and to the problems in the semi-analytical methods that produce too compact and luminous groups., Comment: 17 pages, 8 figures

The main feature of the spatial large-scale galaxy distribution is its intricate network of galaxy filaments. This network is spanned by the galaxy locations that can be interpreted as a three-dimensional point distribution. The global properties of the point process can be measured by different statistical methods, which, however, do not describe directly the structure elements. The morphology of the large scale structure, on the other hand, is an important property of the galaxy distribution. Here we apply an object point process with interactions (the Bisous model) to trace and extract the filamentary network in the presently largest galaxy redshift survey, the Sloan Digital Sky Survey (SDSS). We search for filaments in the galaxy distribution that have a radius of about 0.5 Mpc/h. We divide the detected network into single filaments and present a public catalogue of filaments. We study the filament length distribution and show that the longest filaments reach the length of 60 Mpc/h. The filaments contain 35-40% of the total galaxy luminosity and they cover roughly 5-8% of the total volume, in good agreement with N-body simulations and previous observational results., Comment: 21 pages, 14 figures, accepted for publication in MNRAS

Galaxies are not distributed randomly in the cosmic web but are instead arranged in filaments and sheets surrounding cosmic voids. Observationally there is still no convincing evidence of a link between the properties of galaxies and their host structures. However, by the tidal torque theory (our understanding of the origin of galaxy angular momentum), such a link should exist. Using the presently largest spectroscopic galaxy redshift survey (SDSS) we study the connection between the spin axes of galaxies and the orientation of their host filaments. We use a three dimensional field of orientations to describe cosmic filaments. To restore the inclination angles of galaxies, we use a 3D photometric model of galaxies that gives these angles more accurately than traditional 2D models. We found evidence that the spin axes of bright spiral galaxies have a weak tendency to be aligned parallel to filaments. For elliptical/S0 galaxies, we have a statistically significant result that their spin axes are aligned preferentially perpendicular to the host filaments; we show that this signal practically does not depend on the accuracy of the estimated inclination angles for elliptical/S0 galaxies., Comment: 11 pages, 10 figures. Accepted for publication in MNRAS

We study the relations between the multimodality of galaxy clusters drawn from the SDSS DR8 and the environment where they reside. As cluster environment we consider the global luminosity density field, supercluster membership, and supercluster morphology. We use 3D normal mixture modelling, the Dressler-Shectman test, and the peculiar velocity of cluster main galaxies as signatures of multimodality of clusters. We calculate the luminosity density field to study the environmental densities around clusters, and to find superclusters where clusters reside. We determine the morphology of superclusters with the Minkowski functionals and compare the properties of clusters in superclusters of different morphology. We apply principal component analysis to study the relations between the multimodality parametres of clusters and their environment simultaneously. We find that multimodal clusters reside in higher density environment than unimodal clusters. Clusters in superclusters have higher probability to have substructure than isolated clusters. The superclusters can be divided into two main morphological types, spiders and filaments. Clusters in superclusters of spider morphology have higher probabilities to have substructure and larger peculiar velocities of their main galaxies than clusters in superclusters of filament morphology. The most luminous clusters are located in the high-density cores of rich superclusters. Five of seven most luminous clusters, and five of seven most multimodal clusters reside in spider-type superclusters; four of seven most unimodal clusters reside in filament-type superclusters. Our study shows the importance of the role of superclusters as high density environment which affects the properties of galaxy systems in them., Comment: 16 pages, 12 figures, 2 online tables, accepted for publication in Astronomy and Astrophysics

We search for the presence of substructure, a non-Gaussian, asymmetrical velocity distribution of galaxies, and large peculiar velocities of the main galaxies in galaxy clusters with at least 50 member galaxies, drawn from the SDSS DR8. We employ a number of 3D, 2D, and 1D tests to analyse the distribution of galaxies in clusters: 3D normal mixture modelling, the Dressler-Shectman test, the Anderson-Darling and Shapiro-Wilk tests and others. We find the peculiar velocities of the main galaxies, and use principal component analysis to characterise our results. More than 80% of the clusters in our sample have substructure according to 3D normal mixture modelling, the Dressler-Shectman (DS) test shows substructure in about 70% of the clusters. The median value of the peculiar velocities of the main galaxies in clusters is 206 km/s (41% of the rms velocity). The velocities of galaxies in more than 20% of the clusters show significant non-Gaussianity. While multidimensional normal mixture modelling is more sensitive than the DS test in resolving substructure in the sky distribution of cluster galaxies, the DS test determines better substructure expressed as tails in the velocity distribution of galaxies. Richer, larger, and more luminous clusters have larger amount of substructure and larger (compared to the rms velocity) peculiar velocities of the main galaxies. Principal component analysis of both the substructure indicators and the physical parameters of clusters shows that galaxy clusters are complicated objects, the properties of which cannot be explained with a small number of parameters or delimited by one single test. The presence of substructure, the non-Gaussian velocity distributions, as well as the large peculiar velocities of the main galaxies, shows that most of the clusters in our sample are dynamically young., Comment: 15 pages, 11 figures, 2 online tables, accepted for publication in Astronomy and Astrophysics

Properties of galaxies depend on their large-scale environment. As the influence of active galactic nuclei (AGN) in galaxy evolution is becoming more evident, their large scale environments may help us understand the evolutionary processes leading to activity. The effect of activity can be seen particularly by showing if different types of active galaxies are formed by similar mechanisms. Our aim is to study the supercluster-scale environments of active galaxies up to redshift 0.4. Our data includes quasars, BL Lac objects, Seyfert and radio galaxies. We use a three-dimensional low-resolution luminosity-density field constructed of a sample of luminous red galaxies in the seventh data release of the Sloan Digital Sky Survey. We calculate the average density of this field in a volume of a 3\,$h^{-1}$Mpc sphere around each AGN for estimating the environmental density levels of different types of AGN. This analysis gives us the distribution of AGN in the global environment of superclusters, filaments, and voids. Our results show that while radio-quiet quasars and Seyfert galaxies are mostly located in low-density regions, radio galaxies have higher environmental densities. BL Lac objects usually have low-density environments, but some of them are also in very high density regions. Our results give support to the theory of galaxy evolution where galaxies are affected by two modes of AGN feedback: quasar mode that turns a blue star-forming galaxy into a red and dead one, and radio mode that regulates the growth of massive elliptical galaxies. We conclude that quasars are in lower density environments than radio galaxies most likely because the galaxies in rich environments have evolved to a state suitable for radio-loud activity earlier. Galaxies in poor environment have evolved slower, and are still going through the earlier quasar mode feedback in galaxy evolution., Comment: 11 pages, 5 figures; Accepted for publication in A&A, language corrected

We apply the principal component analysis and Spearman's correlation test to study the properties of superclusters drawn from the SDSS DR7. We analyse possible selection effects in the supercluster catalogue, study the physical and morphological properties of superclusters, find their possible subsets, and determine scaling relations for superclusters. We show that the parameters of superclusters do not correlate with their distance. The correlations between the physical and morphological properties of superclusters are strong. Superclusters can be divided into two populations according to their total luminosity. High-luminosity superclusters form two sets, more elongated systems with the shape parameter K_1/K_2 < 0.5 and less elongated ones with K_1/K_2 > 0.5. The first two principal components account for more than 90% of the variance in the supercluster parameters and define the fundamental plane, which characterises the physical and morphological properties of superclusters. We use principal component analysis to derive scaling relations for superclusters, in which we combine the physical and morphological parameters of superclusters. Structure formation simulations for different cosmologies, and more data about the local and high redshift superclusters are needed to understand better the evolution and the properties of superclusters., Comment: 13 pages, 10 figures, accepted for publication in Astronomy and Astrophysics

We present first results on PLCK G266.6-27.3, a galaxy cluster candidate detected at a signal-to-noise ratio of 5 in the Planck All Sky survey. An XMM-Newton validation observation has allowed us to confirm that the candidate is a bona fide galaxy cluster. With these X-ray data we measure an accurate redshift, z = 0.94 +/- 0.02, and estimate the cluster mass to be M_500 = (7.8 +/- 0.8)e+14 solar masses. PLCK G266.6-27.3 is an exceptional system: its luminosity of L_X(0.5-2.0 keV)=(1.4 +/- 0.05)e+45 erg/s, equals that of the two most luminous known clusters in the z > 0.5 universe, and it is one of the most massive clusters at z~1. Moreover, unlike the majority of high-redshift clusters, PLCK G266.6-27.3 appears to be highly relaxed. This observation confirms Planck's capability of detecting high-redshift, high-mass clusters, and opens the way to the systematic study of population evolution in the exponential tail of the mass function., Comment: 6 pages, 3 figures; final version accepted for publication in A&A ; minor changes in Sec.2.,3.2 and 4.1; Table 1: misprint on R500 error corrected; abundance value added

Our goal is to see how density waves of different scale combine to form voids between galaxy systems of various scale. We perform numerical simulations of structure formation in cubes of size 100 and 256 Mpc/h, with resolutions 256^3 and 512^3 particles and cells. To understand the role of density perturbations of various scale we cut power spectra at scales from 8 to 128 Mpc/h, using in all series identical initial random realisations. We find that small haloes and short filaments form all over the simulation box, if perturbations only up to scale 8 Mpc/h are present. The phenomenon of large multi-scale voids in the cosmic web requires the presence of an extended spectrum of primordial density perturbations. The void phenomenon 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 the combined action of negative sections of medium- and large-scale density perturbations, so that their densities are less than the mean density, and thus during the evolution their densities decrease., Comment: 16 pages, 11 figures, revised version

We study the morphology of a set of superclusters drawn from the SDSS DR7. We calculate the luminosity density field to determine superclusters from a flux- limited sample of galaxies from SDSS DR7, and select superclusters with 300 and more galaxies for our study. The morphology of superclusters is described with the fourth Minkowski functional V3, the morphological signature (the curve in the shapefinder's K1-K2 plane) and the shape parameter (the ratio of the shapefinders K1/K2). We investigate the supercluster sample using multidimensional normal mixture modelling, and use Abell clusters to identify our superclusters with known superclusters and to study the large-scale distribution of superclusters. The superclusters in our sample form three chains of superclusters; one of them is the Sloan Great Wall. Most superclusters have filament-like overall shapes. Superclusters can be divided into two sets; more elongated superclusters are more luminous, richer, have larger diameters, and a more complex fine structure than less elongated superclusters. The fine structure of superclusters can be divided into four main morphological types: spiders, multispiders, filaments, and multibranching filaments. We present the 2D and 3D distribution of galaxies and rich groups, the fourth Minkowski functional, and the morphological signature for all superclusters. Widely different morphologies of superclusters show that their evolution has been dissimilar. A study of a larger sample of superclusters from observations and simulations is needed to understand the morphological variety of superclusters and the possible connection between the morphology of superclusters and their large-scale environment., Comment: Comments: 20 pages, 18 figures, accepted for publication in Astronomy and Astrophysics

We present the results of the study of the morphology and galaxy content of the Sloan Great Wall (SGW). We use the luminosity density field to determine superclusters in the SGW, and the fourth Minkowski functional V_3 and the morphological signature (the K_1-K_2 shapefinders curve) to show the different morphologies of the SGW, from a single filament to a multibranching, clumpy planar system. The richest supercluster in the SGW, SCl~126 and especially its core resemble a very rich filament, while another rich supercluster in the SGW, SCl~111, resembles a "multispider" - an assembly of high density regions connected by chains of galaxies. Using Minkowski functionals we study the substructure of individual galaxy populations determined by their color in these superclusters. We assess the statistical significance of the results with the halo model and smoothed bootstrap. We study the galaxy content and the properties of groups of galaxies in two richest superclusters of the SGW, paying special attention to bright red galaxies (BRGs) and to the first ranked galaxies in SGW groups. About 1/3 of BRGs are spirals. The scatter of colors of elliptical BRGs is smaller than that of spiral BRGs. About half of BRGs and of first ranked galaxies in groups have large peculiar velocities. Groups with elliptical BRGs as their first ranked galaxies populate superclusters more uniformly than the groups, which have a spiral BRG as its first ranked galaxy. The galaxy and group content of the core of the supercluster SCl~126 shows several differences in comparison with the outskirts of this supercluster and with the supercluster SCl~111. Our results suggest that the formation history and evolution of individual neighbour superclusters in the SGW has been different., Comment: Comments: 26 pages, 20 figures, accepted for publication in ApJ

We present the first all-sky sample of galaxy clusters detected blindly by the Planck satellite through the Sunyaev-Zeldovich (SZ) effect from its six highest frequencies. This early SZ (ESZ) sample is comprised of 189 candidates, which have a high signal-to-noise ratio ranging from 6 to 29. Its high reliability (purity above 95%) is further ensured by an extensive validation process based on Planck internal quality assessments and by external cross-identification and follow-up observations. Planck provides the first measured SZ signal for about 80% of the 169 previously-known ESZ clusters. Planck furthermore releases 30 new cluster candidates, amongst which 20 meet the ESZ signal-to-noise selection criterion. At the submission date, twelve of the 20 ESZ candidates were confirmed as new clusters, with eleven confirmed using XMM-Newton snapshot observations, most of them with disturbed morphologies and low luminosities. The ESZ clusters are mostly at moderate redshifts (86% with z below 0.3) and span more than a decade in mass, up to the rarest and most massive clusters with masses above 10^15 Msol., Comment: Accepted for publication in a special issue of A&A, 26 pages, this paper is part of a package of papers describing first results of the Planck mission

Baryon Acoustic Oscillations (BAO) are a feature imprinted in the density field by acoustic waves travelling in the plasma of the early universe. Their fixed scale can be used as a standard ruler to study the geometry of the universe. BAO have been previously detected using correlation functions and power spectra of the galaxy distribution. In this work, we present a new method for the detection of the real-space structures associated with this feature. These baryon acoustic structures are spherical shells with a relatively small density contrast, surrounding high density central regions. We design a specific wavelet adapted to the search for shells, and exploit the physics of the process by making use of two different mass tracers, introducing a specific statistic to detect the BAO features. We show the effect of the BAO signal in this new statistic when applied to the Lambda - Cold Dark Matter (LCDM) model, using an analytical approximation to the transfer function. We confirm the reliability and stability of our method by using cosmological N-body simulations from the MareNostrum Institut de Ci\`encies de l'Espai (MICE). We apply our method to the detection of BAO in a galaxy sample drawn from the Sloan Digital Sky Survey (SDSS). We use the `Main' catalogue to trace the shells, and the Luminous Red Galaxies (LRG) as tracers of the high density central regions. Using this new method, we detect, with a high significance, that the LRGs in our sample are preferentially located close to the centres of shell-like structures in the density field, with characteristics similar to those expected from BAOs. We show that stacking selected shells, we can find their characteristic density profile. We have delineated a new feature of the cosmic web, the BAO shells. As these are real spatial structures, the BAO phenomenon can be studied in detail by examining those shells., Comment: 12 pages, 10 figures, 1 table. Accepted for publication in A&A. v3: General revision of the paper. Added Sect. 3 discussing expected signal in LCDM model, using MICE simulations. Added illustration of localisation and stacking possibilities in Sect. 5. Main results and conclusions unchanged

We follow the evolution of galaxy systems in numerical simulation. Our goal is to understand the role of density perturbations of various scales in the formation and evolution of the cosmic web. We perform numerical simulations with the full power spectrum of perturbations, and with spectrum cut at long wavelengths. Additionally, we have one model, where we cut the intermediate waves. We analyze the density field and study the void sizes and density field clusters in different models. Our analysis shows that the fine structure (groups and clusters of galaxies) is created by small-scale density perturbations of scale $\leq 8$ \Mpc. Filaments of galaxies and clusters are created by perturbations of intermediate scale from $\sim 8$ to $\sim 32$ \Mpc, superclusters of galaxies by larger perturbations. We conclude that the scale of the pattern of the cosmic web is determined by density perturbations of scale up to $\sim 100$ \Mpc. Larger perturbations do not change the pattern of the web, but modulate the richness of galaxy systems, and make voids emptier. The stop of the increase of the scale of the pattern of the cosmic web with increasing scale of density perturbations can probably be explained as the freezing of the web at redshift $z\simeq 0.7$., Comment: 12 pages, 7 figures, accepted for publication in Astronomy and Astrophysics

According to the modern cosmological paradigm galaxies and galaxy systems form from tiny density perturbations generated during the very early phase of the evolution of the Universe. Using numerical simulations we study the evolution of phases of density perturbations of different scales to understand the formation and evolution of the cosmic web. We apply the wavelet analysis to follow the evolution of high-density regions (clusters and superclusters) of the cosmic web. We show that the positions of maxima and minima of density waves (their spatial phases) almost do not change during the evolution of the structure. Positions of extrema of density perturbations are the more stable, the larger is the wavelength of perturbations. Combining observational and simulation data we conclude that the skeleton of the cosmic web was present already in an early stage of structure evolution., Comment: 12 pages, 8 figures, revised version

We have constructed a set of supercluster catalogues for the galaxies from the SDSS survey main and luminous red galaxy (LRG) flux-limited samples. To delineate superclusters, we calculated luminosity density fields using the B3-spline kernel of the radius of 8 Mpc/h for the main sample and 16 Mpc/h for the LRG sample and define regions with densities over a selected threshold as superclusters, while utilising almost the whole volume of both samples. We created two types of catalogues, one with an adaptive local threshold and a set of catalogues with different global thresholds. We describe the supercluster catalogues and their general properties. Using smoothed bootstrap, we find uncertainty estimates for the density field and use these to attribute confidence levels to the catalogue objects. We have also created a test catalogue for the galaxies from the Millennium simulation to compare the simulated and observed superclusters and to clarify the methods we use. We find that the superclusters are well-defined systems, and the properties of the superclusters of the main and LRG samples are similar. We also show that with adaptive local thresholds we get a sample of superclusters, the properties of which do not depend on their distance from the observer. The Millennium galaxy catalogue superclusters are similar to those observed., Comment: 14 pages, 16 figures. Accepted by A&A

We study the influence of the environment on the evolution of galaxies by investigating the luminosity function (LF) of galaxies of different morphological types and colours at different environmental density levels. We construct the LFs separately for galaxies of different morphology (spiral and elliptical) and of different colours (red and blue) using data from the Sloan Digital Sky Survey (SDSS), correcting the luminosities for the intrinsic absorption. We use the global luminosity density field to define different environments, and analyse the environmental dependence of galaxy morphology and colour. The smoothed bootstrap method is used to calculate confidence regions of the derived luminosity functions. We find a strong environmental dependency for the LF of elliptical galaxies. The LF of spiral galaxies is almost environment independent, suggesting that spiral galaxy formation mechanisms are similar in different environments. Absorption by the intrinsic dust influences the bright-end of the LF of spiral galaxies. After attenuation correction, the brightest spiral galaxies are still about 0.5 mag less luminous than the brightest elliptical galaxies, except in the least dense environment, where spiral galaxies dominate the LF at every luminosity. Despite the extent of the SDSS survey, the influence of single rich superclusters is present in the galactic LF of the densest environment., Comment: 14 pages, 16 figures, accepted for publication in A&A

We present the results of the study of the substructure and galaxy content of ten rich clusters of galaxies in three different superclusters of the Sloan Great Wall. We determine the substructure in clusters using the 'Mclust' package from the 'R' statistical environment and analyse their galaxy content. We analyse the distribution of the peculiar velocities of galaxies in clusters and calculate the peculiar velocity of the first ranked galaxy. We show that clusters in our sample have more than one component; in some clusters different components also have different galaxy content. We find that in some clusters with substructure the peculiar velocities of the first ranked galaxies are large. All clusters in our sample host luminous red galaxies. They can be found both in the central areas of clusters as well as in the outskirts, some of them have large peculiar velocities. About 1/3 of red galaxies in clusters are spirals. The scatter of colours of red ellipticals is in most clusters larger than that of red spirals. The presence of substructure in rich clusters, signs of possible mergers and infall, as well as the large peculiar velocities of the first ranked galaxies suggest that the clusters in our sample are not yet virialized. We present merger trees of dark matter haloes in an N-body simulation to demonstrate the formation of present-day dark matter haloes via multiple mergers during their evolution. In simulated dark matter haloes we find a substructure similar to that in observed clusters., Comment: 19 pages, 44 figures, accepted for publication in Astronomy and Astrophysics

Context. The main feature of the spatial large-scale galaxy distribution is an intricate network of galaxy filaments. Although many attempts have been made to quantify this network, there is no unique and satisfactory recipe for that yet. Aims. The present paper compares the filaments in the real data and in the numerical models, to see if our best models reproduce statistically the filamentary network of galaxies. Methods. We apply an object point process with interactions (the Bisous process) to trace and describe the filamentary network both in the observed samples (the 2dFGRS catalogue) and in the numerical models that have been prepared to mimic the data.We compare the networks. Results. We find that the properties of filaments in numerical models (mock samples) have a large variance. A few mock samples display filaments that resemble the observed filaments, but usually the model filaments are much shorter and do not form an extended network. Conclusions. We conclude that although we can build numerical models that are similar to observations in many respects, they may fail yet to explain the filamentary structure seen in the data. The Bisous-built filaments are a good test for such a structure., Comment: 13 pages, accepted for publication in Astronomy and Astrophysics

For the first time spectroscopic galaxy redshift surveys are reaching the scales where galaxies can be studied together with the nearest quasars. This gives an opportunity to study the dependence between the activity of a quasar and its environment in a more extensive way than before. We study the spatial distribution of galaxies and groups of galaxies in the environments of low redshift quasars in the Sloan Digital Sky Survey (SDSS). Our aim is to understand how the nearby quasars are embedded in the local and global density field of galaxies and how the environment affects quasar activity. We analyse the environments of nearby quasars using number counts of galaxies. We also study the dependence of group properties to their distance to the nearest quasar. The large scale environments are studied by analysing the locations of quasars in the luminosity density field. Our study of the number counts of galaxies in quasar environments shows an underdensity of bright galaxies at a few Mpc from quasars. Also, the groups of galaxies that have a quasar closer than 2Mpc are poorer and less luminous than in average. Our analysis on the luminosity density field shows that quasars clearly avoid rich superclusters. Nearby quasars seem to be located in outskirts of superclusters or in filaments connecting them. Our results suggest that quasar evolution may be affected by density variations both on supercluster scales and in the local environment., Comment: Accepted to A&A

We present a morphological study of the two richest superclusters from the 2dF Galaxy Redshift Survey (SCL126, the Sloan Great Wall, and SCL9, the Sculptor supercluster). We use Minkowski functionals, shapefinders, and galaxy group information to study the substructure of these superclusters as formed by different populations of galaxies. We compare the properties of grouped and isolated galaxies in the core region and in the outskirts of superclusters. The fourth Minkowski functional $V_3$ and the morphological signature $K_1$- $K_2$ show a crossover from low-density morphology (outskirts of supercluster) to high-density morphology (core of supercluster) at mass fraction $m_f \approx 0.7$. The galaxy content and the morphology of the galaxy populations in supercluster cores and outskirts is different. The core regions contain a larger fraction of early type, red galaxies, and richer groups than the outskirts of superclusters. In the core and outskirt regions the fine structure of the two prominent superclusters as delineated by galaxies from different populations also differs. Our results suggest that both local (group/cluster) and global (supercluster) environments are important in forming galaxy morphologies and colors (and determining the star formation activity). The differences between the superclusters indicate that these superclusters have different evolutional histories (Abridged)., Comment: 23 pages, accepted for publication in The Astrophysical Journal

We extract groups of galaxies from the SDSS Data Release 5 with the purpose of studying the supercluster-void network and environmental properties of groups therein. We use a modified friends-of-friends (FoF) method with adopted variable linking length in transverse and radial direction to eliminate selection effects and to find reliably as many groups as possible to track the supercluster network. We take into account various selection effects due to the use of a magnitude limited sample. To determine linking length scaling we study the luminosity-density relation in observed groups. We follow the changes in group sizes and mean galaxy number densities within groups when shifting nearby groups to larger distances. As a result we show that the linking length should be a slowly growing function with distance. Our final sample contains 17143 groups in the equatorial, and 33219 groups in the northern part of the DR5 survey with membership N_g >= 2. The group catalogue is available at our web-site http://www.obs.ee/~erik/index.html. Due to a narrow magnitude window in the SDSS the group catalogue based on this survey has been obtained by moderately growing linking length scaling law up to redshift z = 0.12. Above this redshift the scaling law turns down. In the redshift range z=0.12 - 0.2 only the cores are detected. Along with applying weights when calculating luminosities it is possible to use groups for determination of the large-scale luminosity-density field., Comment: 11 pages, 15 figures, submitted to Astronomy and Astrophysics

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., Comment: 11 pages, 6 figures, submitted to Astronomy and Astrophysics

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., Comment: 14 pages, 8 figures, submitted to Astronomy and Astrophysics

The lecture introduces a trous wavelet transforms, explains how to estimate the spatial density for galaxy distributions, and, finally, how to describe the morphology of cosmological density fields. An example application of these methods to the 2dFGRS gives unexpected results., Comment: 39 pages, 22 figures, to be published in the proceedings of the summer school "Data Analysis in Cosmology", Valencia, 2004

If the concordance $\Lambda$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 $\Lambda$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., Comment: 11 pages, 16 figures

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 $\delta \approx 7.5$, in poor superclusters $\delta \approx 6.0$. Rich superclusters contain high density cores with densities $\delta > 10$ 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 ($\delta > 10$) 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., Comment: 13 pages, 10 figures, submitted to Astronomy and Astrophysics

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., Comment: 6 pages, 3 Figures, submitted for Astronomy and Astrophysics

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., Comment: 15 pages, 13 Figures, submitted for Astronomy and Astrophysics

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., Comment: 16 pages, 11 figures, submitted for Astronomy and Astrophysics. High-resolution pdf file and supplementary data can be found at http://www.aai.ee/~maret/2dfscl.html

We have developed a method based on wavelets to obtain the true underlying smooth density from a point distribution. The goal has been to reconstruct the density field in an optimal way ensuring that the morphology of the reconstructed field reflects the true underlying morphology of the point field which, as the galaxy distribution, has a genuinely multiscale structure, with near-singular behavior on sheets, filaments and hotspots. If the discrete distributions are smoothed using Gaussian filters, the morphological properties tend to be closer to those expected for a Gaussian field. The use of wavelet denoising provide us with a unique and more accurate morphological description., Comment: Accepted for publication in ApJ

We present a new fast method for simulating pencil-beam type light-cones, using the MLAPM-code (Multi Level Adaptive Particle Mesh) with light-cone additions. We show that by a careful choice of the light-cone orientation, it is possible to avoid extra periodicities in the light-cone. As an example, we apply the method to simulate a 6 Gpc deep light-cone, create the dark matter halo catalogue for the light-cone and study the evolution of haloes from $z=6$ up to the present time. We determine the spatial density of the haloes, their large-scale correlation function, and study the evolution of the mass function. We find a surprisingly simple relation for the dependence of halo maximum mass on redshift, and apply it to derive redshift limits for bright quasars., Comment: 9 pages, 9 figures, submitted for Astronomy and Astrophys

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), Comment: 9 pages, 9 figures, submitted to A&A, version with high quality figures available at http://www.aai.ee/~maret/2dfgr.html

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., Comment: 9 pages, 7 figures, submitted for Astronomy and Astrophysics

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., Comment: 12 pages, 8 figures, submitted for Astronomy and Astrophysics

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., Comment: 12 pages of LaTex text with 12 ps figures, submitted for Proceedings of the workshop "Nearby Large-Scale Structures and the Zone of Avoidance", Cape Town, 28 March - 02 April 2004. pdf file with high-quality figures available at http://www.aai.ee/~einasto

Galaxies are arranged in interconnected walls and filaments forming a cosmic web encompassing huge, nearly empty, regions between the structures. Many statistical methods have been proposed in the past in order to describe the galaxy distribution and discriminate the different cosmological models. We present in this paper results relative to the use of new statistical tools using the 3D isotropic undecimated wavelet transform, the 3D ridgelet transform and the 3D beamlet transform. We show that such multiscale methods produce a new way to measure in a coherent and statistically reliable way the degree of clustering, filamentarity, sheetedness, and voidedness of a dataset, Comment: 26 pages, 20 figures. Submitted to EURASIP Journal on Applied Signal Processing (special issue on "Applications of Signal Processing in Astrophysics and Cosmology")

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), Comment: 19 pages LaTeX text, 15 PostScript Figures, submitted to Astronomy and Astrophysics

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 \Omega_m=0.3 and \Omega_\Lambda =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., Comment: 10 pages LaTeX text, 8 PostScript Figures, 1 jpg Figure (4a, 4b), submitted to Astronomy and Astrophysics