Characteristic density contrasts in the evolution of superclusters. The case of A2142 supercluster

The formation and evolution of the cosmic web in which galaxy superclusters are the largest relatively isolated objects is governed by a gravitational attraction of dark matter and antigravity of dark energy (cosmological constant). We study the characteristic density contrasts in the spherical collapse model for several epochs in the supercluster evolution and their dynamical state. We analysed the density contrasts for the turnaround, future collapse and zero gravity in different LCDM models and applied them to study the dynamical state of the supercluster A2142 with an almost spherical main body. The analysis of the supercluster A2142 shows that its high-density core has already started to collapse. The zero-gravity line outlines the outer region of the main body of the supercluster. In the course of future evolution the supercluster may split into several collapsing systems. The various density contrasts presented in our study and applied to the supercluster A2142 offer a promising way to characterise the dynamical state and expected future evolution of galaxy superclusters.

Unusual A2142 supercluster with a collapsing core: distribution of light and mass

We study the distribution, masses, and dynamical properties of galaxy groups in the A2142 supercluster. We analyse the global luminosity density distribution in the supercluster and divide the supercluster into the high-density core and the low-density outskirts regions. We find galaxy groups and filaments in the regions of different global density, calculate their masses and mass-to-light ratios and analyse their dynamical state with several 1D and 3D statistics. We use the spherical collapse model to study the dynamical state of the supercluster. We show that in A2142 supercluster groups and clusters with at least ten member galaxies lie along an almost straight line forming a 50 Mpc/h long main body of the supercluster. The A2142 supercluster has a very high density core surrounded by lower-density outskirt regions. The total estimated mass of the supercluster is M_est = 6.2 10^{15}M_sun. More than a half of groups with at least ten member galaxies in the supercluster lie in the high-density core of the supercluster, centered at the rich X-ray cluster A2142. Most of the galaxy groups in the core region are multimodal. In the outskirts of the supercluster, the number of groups is larger than in the core, and groups are poorer. The orientation of the cluster A2142 axis follows the orientations of its X-ray substructures and radio halo, and is aligned along the supercluster axis. The high-density core of the supercluster with the global density D8 > 17 and perhaps with D8 > 13 may have reached the turnaround radius and started to collapse. A2142 supercluster with luminous, collapsing core and straight body is an unusual object among galaxy superclusters. In the course of the future evolution the supercluster may be split into several separate systems.

Tracing high redshift cosmic web with quasar systems

We trace the cosmic web at redshifts 1.0 <= z <= 1.8 using the quasar data from the SDSS DR7 QSO catalogue (Schneider et al. 2010). We apply a friend-of-friend (FoF) algorithm to the quasar and random catalogues to determine systems at a series of linking lengths, and analyse richness and sizes of these systems. At the linking lengths l <= 30 Mpc/h the number of quasar systems is larger than the number of systems detected in random catalogues, and systems themselves have smaller diameters than random systems. The diameters of quasar systems are comparable to the sizes of poor galaxy superclusters in the local Universe, the richest quasar systems have four members. The mean space density of quasar systems is close to the mean space density of local rich superclusters. At intermediate linking lengths (40 <= l <= 70 Mpc/h) the richness and length of quasar systems are similar to those derived from random catalogues. Quasar system diameters are similar to the sizes of rich superclusters and supercluster chains in the local Universe. At the linking length 70 Mpc/h the richest systems of quasars have diameters exceeding 500 Mpc/h. The percolating system which penetrate the whole sample volume appears in quasar sample at smaller linking length than in random samples (85 Mpc/h). Quasar luminosities in systems are not correlated with the system richness. Quasar system catalogues at our web pages http://www.aai.ee/~maret/QSOsystems.html serve as a database to search for superclusters of galaxies and to trace the cosmic web at high redshifts.

Anatomy of luminosity functions: the 2dFGRS example

Aims. We use the 2dF Galaxy Redshift Survey to derive the luminosity function (LF) of the first-ranked (brightest) group/cluster galaxies, the LF of second-ranked, satellite and isolated galaxies, and the LF of groups of galaxies. Methods. We investigate the LFs of different samples in various environments: in voids, filaments, superclusters and supercluster cores. We compare the derived LFs with the Schechter and double-power-law analytical expressions. We also analyze the luminosities of isolated galaxies. Results. We find strong environmental dependency of luminosity functions of all populations. The luminosities of first-ranked galaxies have a lower limit, depending on the global environment (higher in supercluster cores, and absent in voids). The LF of second-ranked galaxies in high-density regions is similar to the LF of first-ranked galaxies in a lower-density environment. The brightest isolated galaxies can be identified with first-ranked galaxies at distances where the remaining galaxies lie outside the observational window used in the survey. Conclusions. The galaxy and cluster LFs can be well approximated by a double-power-law; the widely used Schechter function does not describe well the bright end and the bend of the LFs. Properties of the LFs reflect differences in the evolution of galaxies and their groups in different environments.