Search

We present two new examples of galaxies undergoing transformation in the Shapley supercluster core. These low-mass (M* ~ 0.4-1 ? 1010 Mʘ) galaxies are members of the two clusters SC 1329-313 (z ~ 0.045) and SC 1327-312 (z ~ 0.049). Integral-field spectroscopy complemented by imaging in the ugriK bands and in Ha narrow band is used to disentangle the effects of tidal interaction (TI) and ram-pressure stripping (RPS). In both galaxies, SOS 61086 and SOS 90630, we observe one-sided extraplanar ionized gas extending respectively ~30 and ~41 kpc in projection from their discs. The galaxies' gaseous discs are truncated, and the kinematics of the stellar and gas components are decoupled, supporting the RPS scenario. The emission of the ionized gas extends in the direction of a possible companion for both galaxies suggesting a TI. The overall gas velocity field of SOS 61086 is reproduced by ad hoc N-body/hydrodynamical simulations of RPS acting almost face-on and starting ~250 Myr ago, consistent with the age of the young stellar populations. A link between the observed gas stripping and the cluster-cluster interaction experienced by SC 1329-313 and A3562 is suggested. Simulations of ram pressure acting almost edge-on are able to fully reproduce the gas velocity field of SOS 90630, but cannot at the same time reproduce the extended tail of outflowing gas. This suggests that an additional disturbance from a TI is required. This study adds a piece of evidence that RPS may take place in different environments with different impacts and witnesses the possible effect of cluster-cluster merger on RPS. [ABSTRACT FROM AUTHOR]

Traditionally, galaxy clusters have been expected to retain all the material accreted since their formation epoch. For this reason, their matter content should be representative of the Universe as a whole, and thus their baryon fraction should be close to the Universal baryon fraction b= m. We make use of the sample of the 100 brightest galaxy clusters discovered in the XXL Survey to investigate the fraction of baryons in the form of hot gas and stars in the cluster population. Since it spans a wide range of mass (1013-1015 M⊙) and redshift (0:05-1:1) and benefits from a large set of multiwavelength data, the XXL-100-GC sample is ideal for measuring the global baryon budget of massive halos. We measure the gas masses of the detected halos and use a mass-temperature relation directly calibrated using weak-lensing measurements for a subset of XXL clusters to estimate the halo mass. We find that the weak-lensing calibrated gas fraction of XXL-100-GC clusters is substantially lower than was found in previous studies using hydrostatic masses. Our best-fit relation between gas fraction and mass reads fgas;500 = 0:055+0:007 -0:006 M500=1014 M⊙ 0:21+0:11 -0:10. The baryon budget of galaxy clusters therefore falls short of the Universal baryon fraction by about a factor of two at r500;MT. Our measurements require a hydrostatic bias 1-b = MX=MWL = 0:72+0:08 -0:07 to match the gas fraction obtained using lensing and hydrostatic equilibrium, which holds independently of the instrument considered. Comparing our gas fraction measurements with the expectations from numerical simulations, we find that our results favour an extreme feedback scheme in which a significant fraction of the baryons are expelled from the cores of halos. This model is, however, in contrast with the thermodynamical properties of observed halos, which might suggest that weak-lensing masses are overestimated. In light of these results, we note that a mass bias 1 - b = 0:58 as required to reconcile Planck cosmic microwave background and cluster counts should translate into an even lower baryon fraction, which poses a major challenge to our current understanding of galaxy clusters. [ABSTRACT FROM AUTHOR]

Context: The XXL Survey is the largest homogeneous and contiguous survey carried out with XMM-Newton. Covering an area of 50 deg² distributed over two fields, it primarily investigates the large-scale structures of the Universe using the distribution of galaxy clusters and active galactic nuclei as tracers of the matter distribution. Aims: Given its depth and sky coverage, XXL is particularly suited to systematically unveiling the clustering of X-ray clusters and to identifying superstructures in a homogeneous X-ray sample down to the typical mass scale of a local massive cluster. Methods: A friends-of-friends algorithm in three-dimensional physical space was run to identify large-scale structures. In this paper we report the discovery of the highest redshift supercluster of galaxies found in the XXL Survey. We describe the X-ray properties of the clusters members of the structure and the optical follow-up. Results: The newly discovered supercluster is composed of six clusters of galaxies at a median redshift z ~ 0:43 and distributed across ~300×150 (10×5 Mpc) on the sky. This structure is very compact with all the clusters residing in oneXMMpointing; for this reason this is the first supercluster discovered with the XXL Survey. Photometric redshifts from the CFHTLS (Canada-France-Hawaii Telescope Legacy Survey) data release T0007 placed the supercluster at an approximate redshift of zphot ~ 0:45; subsequent spectroscopic follow-up with WHT (William Herschel Telescope) and NTT (New Technology Telescope) confirmed a median redshift of z ~ 0:43. An estimate of the X-ray mass and luminosity of this supercluster returns values of 1:7 × 1015 M⊙ and of 1:68 × 1044 erg s-1, respectively, and a total gas mass of Mgas = 9:3 × 1013 M⊙. These values put XLSSC-e at the average mass range of superclusters; its appearance, with two members of equal size, is quite unusual with respect to other superclusters and provides a unique view of the formation process of a massive structure. [ABSTRACT FROM AUTHOR]

Context: This article belongs to the first series of XXL publications. It presents multifibre spectroscopic observations of three 0.55 deg² fields in the XXL Survey, which were selected on the basis of their high density of X-ray-detected clusters. The observations were obtained with the AutoFib2+WYFFOS (AF2) wide-field fibre spectrograph mounted on the 4.2 m William Herschel Telescope. Aims: The paper first describes the scientific rationale, the preparation, the data reduction, and the results of the observations, and then presents a study of active galactic nuclei (AGN) within three superclusters. Methods: To determine the redshift of galaxy clusters and AGN, we assign high priority to a) the brightest cluster galaxies (BCGs), b) the most probable cluster galaxy candidates, and c) the optical counterparts of X-ray point-like sources. We use the outcome of the observations to study the projected (2D) and the spatial (3D) overdensity of AGN in three superclusters. Results: We obtained redshifts for 455 galaxies in total, 56 of which are counterparts of X-ray point-like sources. We were able to determine the redshift of the merging supercluster XLSSC-e, which consists of six individual clusters at z ~ 0.43, and we confirmed the redshift of supercluster XLSSC-d at z ~ 0.3. More importantly, we discovered a new supercluster, XLSSC-f, that comprises three galaxy clusters also at z ~ 0.3.We find a significant 2D overdensity of X-ray point-like sources only around the supercluster XLSSC-f. This result is also supported by the spatial (3D) analysis of XLSSC-f, where we find four AGN with compatible spectroscopic redshifts and possibly one more with compatible photometric redshift. In addition, we find two AGN (3D analysis) at the redshift of XLSSC-e, but no AGN in XLSSC-d. Comparing these findings with the optical galaxy overdensity we conclude that the total number of AGN in the area of the three superclusters significantly exceeds the field expectations. All of the AGN found have luminosities below 7 1042 erg s-1. Conclusions: The difference in the AGN frequency between the three superclusters cannot be explained by the present study because of small number statistics. Further analysis of a larger number of superclusters within the 50 deg² of the XXL is needed before any conclusions on the effect of the supercluster environment on AGN can be reached. [ABSTRACT FROM AUTHOR]

A prismatic gas-cooled very high temperature reactor (VHTR) is being developed under the next generation nuclear program. One of the concerns for the reactor design is the effects of a loss of flow accident (LOFA) where the coolant circulators are lost for some reason, causing a loss of forced coolant flow through the core. In the previous studies, the natural circulation in the whole reactor vessel (RV) was obtained by segmentation strategies if the computational fluid dynamic (CFD) analysis with a sufficiently refined mesh was conducted, due to the limits of computer capability. The computational domains in the previous studies were segmented sections which were small flow region models, such as 1/12 sectors, or a combination of a few number of the 1/12 sector (ranging from 2 to 15) using geometric symmetry, for a full dome region. The present paper investigates the flow and heat transfer for a much larger flow region model, a 1/12 core model, using high performance computing. The computation meshes for 1/12 sector and 1/12 reactor core are of 7.8 M and ∼531 M, respectively. Over 85,000 and 35,000 iterations for steady and transient (100 s) calculations are required to achieve convergence, respectively. ∼0.1 min CPU time was required using 192 computer cores for the 1/12 sector model and ∼1.3 min CPU time using 768 cores in parallel for the 1/12 core model, for every iteration, using ALPS, Advanced Large-scale Parallel Superclusters. For the LOFA transient condition, this study employs both laminar flow and different turbulence models to characterize the phenomenon of natural convection. The result of Realizable k – ɛ turbulence model (RKE) model is the most conservative one in the heated blocks (channels) regions, but the result of laminar flow is the most conservative one in the plenum regions. The comparisons of the results from large and small models suggest that large flow model is needed to obtain accurate prediction. [ABSTRACT FROM AUTHOR]

We present the first measurement of individual cluster mass estimates using weak lensing size and flux magnification. Using data from the HST STAGES (Space Telescope A901/902 Galaxy Evolution Survey) survey of the A901/902 supercluster we detect the four known groups in the supercluster at high significance using magnification alone. We discuss the application of a fully Bayesian inference analysis, and investigate a broad range of potential systematics in the application of the method. We compare our results to a previous weak lensing shear analysis of the same field finding the recovered signal-to-noise of our magnification-only analysis to range from 45 to 110 per cent of the signal-to-noise in the shear-only analysis. On a case-bycase basis we find consistent magnification and shear constraints on cluster virial radius, and finding that for the full sample, magnification constraints to be a factor 0.77 ± 0.18 lower than the shear measurements. [ABSTRACT FROM AUTHOR]

The Shapley Supercluster Survey is a multi-wavelength survey covering an area of ~23 deg² (~260 Mpc² at z = 0.048) around the supercluster core, including nine Abell and two poor clusters, having redshifts in the range 0.045-0.050. The survey aims to investigate the role of the cluster-scale mass assembly on the evolution of galaxies, mapping the effects of the environment from the cores of the clusters to their outskirts and along the filaments. The optical (ugri) imaging acquired with OmegaCAM on the VLT Survey Telescope is essential to achieve the project goals providing accurate multi-band photometry for the galaxy population down to m* + 6. We describe the methodology adopted to construct the optical catalogues and to separate extended and point-like sources. The catalogues reach average 5s limiting magnitudes within a 3 arcsec diameter aperture of ugri = [24.4,24.6,24.1,23.3] and are 93 percent complete down to ugri = [23.8,23.8,23.5,22.0] mag, corresponding to ~m*r + 8.5. The data are highly uniform in terms of observing conditions and all acquired with seeing less than 1.1 arcsec full width at half-maximum. The median seeing in r band is 0.6 arcsec, corresponding to 0.56 kpc h-170 at z = 0.048. While the observations in the u, g and r bands are still ongoing, the i-band observations have been completed, and we present the i-band catalogue over the whole survey area. The latter is released and it will be regularly updated, through the use of the Virtual Observatory tools. This includes 734 319 sources down to i = 22.0 mag and it is the first optical homogeneous catalogue at such a depth, covering the central region of the Shapley supercluster. [ABSTRACT FROM AUTHOR]

According to the standard cosmological scenario, superclusters are objects that have just passed the turn-around point and are collapsing. The dynamics of very few superclusters have been analysed up to now. In this paper, we study the supercluster SC0028-0005, at redshift 0.22, identify the most prominent groups and/or clusters that make up the supercluster, and investigate the dynamic state of this structure. For the membership identification, we have used photometric and spectroscopic data from Sloan Digital Sky Survey Data Release 10, finding six main structures in a flat spatial distribution. We have also used a deep multiband observation with MegaCam/Canada-France-Hawaii Telescope to estimate de mass distribution through the weak-lensing effect. For the dynamical analysis, we have determined the relative distances along the line of sight within the supercluster using the Fundamental Plane of early-type galaxies. Finally, we have computed the peculiar velocities of each of the main structures. The 3D distribution suggests that SC0028-005 is indeed a collapsing supercluster, supporting the formation scenario of these structures. Using the spherical collapse model, we estimate that the mass within r = 10 Mpc should lie between 4 and 16 × 1015 M⊙. The farthest detected members of the supercluster suggest that within ~60 Mpc the density contrast is δ ~ 3 with respect to the critical density at z = 0.22, implying a total mass of ~4.6-16 × 1017 M⊙, most of which in the form of low-mass galaxy groups or smaller substructures. [ABSTRACT FROM AUTHOR]

Classic molecular dynamics simulations were carried out to monitor the solid and liquid-like regions in Zr 46 Cu 46 Al 8 metallic glass. Based on Voronoi tessellation analysis, this work illustrates that the medium range networks are related to the local fivefold symmetry. Not only atoms with high degree of local fivefold symmetry (Kasper polyhedra) form percolated networks, but also atoms with low degree of fivefold symmetry tend to build up interconnected superclusters. In addition, strong avoidance is observed between these two kinds of atoms. Such spatial heterogeneity is analyzed in terms of its dependence on atomic level stress. Starting from the networks formed by these two kinds of atoms, they are respectively assumed to be solid and liquid-like regions. Our quantitative monitoring of von Mises shear strain suggests that liquid-like networks are fertile sites for plastic deformation, while the backbones formed by atoms with high degree of fivefold symmetry are resistant to shear events. Such investigations on solid and liquid-like regions have implications for the structural and mechanical heterogeneity reported in metallic glasses. [ABSTRACT FROM AUTHOR]

Context. Superclusters of galaxies can be used to test cosmological models of the formation and evolution of the largest structures in the cosmic web, and of galaxy and cluster evolution in superclusters. Aims. We study the distribution, masses, and dynamical properties of galaxy groups in the A2142 supercluster. Methods. 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 these regions, calculate their masses and mass-tolight ratios and analyse their dynamical state with 1D and 3D statistics. We use the spherical collapse model to study the dynamical state of the supercluster. Results. In the A2142 supercluster rich groups and clusters lie along an almost straight line forming the 50 h-1 Mpc long main body of the supercluster. The A2142 supercluster has a very high density core surrounded by lower-density outskirts. The total estimated mass of the supercluster is Mest = 6.2 ×1015Mo. More than a half of groups with at least ten member galaxies in the supercluster lie in the high-density core of the supercluster, centred at the X-ray cluster A2142. Most of the 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 axis of the cluster A2142 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 started to collapse. Conclusions. A2142 supercluster with collapsing core and straight body, is an unusual object among superclusters. In the course of the future evolution, the supercluster may split into several systems. [ABSTRACT FROM AUTHOR]

We report the results of measurement and comparison of masses for a sample of 29 groups and clusters of galaxies ( z < 0.1). We use the SDSSDR7 archive data to determine dynamical masses from the one-dimensional dispersion of line-of-sight velocities for virialized regions of radii R and R. Our method for determination of effective radii of galaxy systems fromthe cumulative distribution of the number of galaxies depending on squared clustercentric distance allowed us to estimate masses M (within R), which are related to the masses contained inside R: M ~ 1.65 M. A comparison of the inferred dynamic masses and the hydrostatic masses determined from the radiation of hot gas in galaxy groups and clusters (based on published data) led us to conclude that the inferred masses for the main sample of 21 groups and clusters agree to within 12%. These systems also obey the relation M ~ 1.65 M. For the remaining eight systems, which are mostly located in the Hercules supercluster, the discrepancy between the hydrostatic and the dynamic masses amounts to 2 σ. This discrepancy is most likely due to the incompleteness of the formation processes of these clusters via hierarchical merger in the region of the rich Hercules supercluster. [ABSTRACT FROM AUTHOR]

A new analytical model for constraining the extent of gravitationally bound structure in the Universe is presented. This model is based on a simple modification of the spherical collapse model (SCM), and its performance in predicting the limits of bound structure in N-body simulations is compared to that of two previous models with the aid of new software named COLDGAS - compute unified device architecture object location determination in GADGET2 snapshots - which was developed by the author. All of these models can be distilled down to a single unique parameter ξ, here named the critical parameter, which was found to have values of 3 and 1.18 from the previous studies, and a value of 1.89 from the modified SCM. While still on the conservative side, this new model tends to better identify what structure is gravitationally bound in simulations. All three analytical models are applied to the Corona Borealis supercluster, with the modified SCM and ξ = 1.18 model making predictions that are in agreement with recent work showing that A2056, A2061, A2065, A2067, and A2089 comprise a gravitationally bound supercluster. As an additional test, the modified SCM is used to estimate the mass within the turn-around radius of the Virgo cluster, providing results in good agreement with studies relating the virial mass of clusters to the total mass within turn-around. [ABSTRACT FROM AUTHOR]

We present evidence of the gravitational lensing of the cosmic microwave background by 1013 solar mass dark matter halos. Lensing convergence maps from the Atacama Cosmology Telescope Polarimeter (ACTPol) are stacked at the positions of around 12000 optically selected CMASS galaxies from the SDSS-III/BOSS survey. The mean lensing signal is consistent with simulated dark matter halo profiles and is favored over a null signal at 3.2σ significance. This result demonstrates the potential of microwave background lensing to probe the dark matter distribution in galaxy group and galaxy cluster halos. [ABSTRACT FROM AUTHOR]

We present a detailed study of the extremely isolated Sdm galaxy UGC 4722 (MB = -17.4) located in the nearby Lynx-Cancer void. UGC 4722 is a member of the Catalogue of Isolated Galaxies, and has also been identified as one of the most isolated galaxies in the Local Supercluster. Optical images of the galaxy however show that it has a peculiar morphology with an elongated ~14 kpc-long plume. New observations with the Russian 6-m telescope (BTA) and the Giant Metrewave Radio Telescope (GMRT) of the ionized and neutral gas in UGC 4722 reveal the second component responsible for the disturbed morphology of the system. This is a small, almost completely destroyed, very gas-rich dwarf (MB = -15.2, M(HI)/LB ~ 4.3) We estimate the oxygen abundance for both galaxies to be 12 + log (O/H) ~ 7.5-7.6 which is two to three times lower than what is expected from the luminosity-metallicity relation for similar galaxies in denser environments. The ugr colours of the plume derived from Sloan Digital Sky Survey (SDSS) images are consistent with a simple stellar population with a post starburst age of 0.45-0.5 Gyr. This system hence appears to be the first known case of a minor merger with a prominent tidal feature consisting of a young stellar population. [ABSTRACT FROM AUTHOR]

The Friedmann--Lemaître--Robertson-Walker (FLRW) metric assumes comoving spatial rigidity of metrical properties. The curvature term in comoving coordinates is environment independent and cannot evolve. In the standard model, structure formation is interpreted accordingly: structures average out on the chosen metrical background, which remains rigid in comoving coordinates despite nonlinear structure growth. The latter claim needs to be tested, since it is a hypothesis that is not derived using general relativity. We introduce a test of the comoving rigidity assumption by measuring the two-point autocorrelation function on comoving scales -- assuming FLRW comoving spatial rigidity -- in order to detect shifts in the baryon acoustic oscillation (BAO) peak location for luminous red galaxy (LRG) pairs of the Sloan Digital Sky Survey Data Release 7. In tangential directions, subsets of pairs overlapping with superclusters or voids show the BAO peak. The tangential BAO peak location for overlap with Nadathur & Hotchkiss superclusters is 4.3 ±1.6 h-1 Mpc less than that for LRG pairs unselected for supercluster overlap, and 6.6 ± 2.8 h-1 Mpc less than that of the complementary pairs. Liivamagi et al. superclusters give corresponding differences of 3.7 ± 2.9 h-1 Mpc and 6.3 ± 2.6 h-1 Mpc, respectively. We have found moderately significant evidence (Kolmogorov-Smirnov tests suggest very significant evidence) that the BAO peak location for supercluster-overlapping pairs is compressed by about 6 per cent compared to that of the complementary sample, providing a potential challenge to FLRW models and a benchmark for predictions from models based on an averaging approach that leaves the spatial metric a priori unspecified. [ABSTRACT FROM AUTHOR]

We examine the integrated Sachs-Wolfe (ISW) imprint of voids and superclusters on the cosmic microwave background. We first study results from the Jubilee N-body simulation. From Jubilee, we obtain the full-sky ISW signal from structures out to redshift z=1.4 and a mock luminous red galaxy catalogue. We confirm that the expected signal in the concordance Λ cold dark matter (ΛCDM) model is very small and likely to always be much smaller than the anisotropies arising at the last scattering surface. Any current detections of such an imprint must, therefore, predominantly arise from something other than an ISW effect in a ΛCDM universe. Using the simulation as a guide, we then look for the signal using a catalogue of voids and superclusters from the Sloan Digital Sky Survey. We find a result that is consistent with the ΛCDM model, i.e. a signal consistent with zero. [ABSTRACT FROM AUTHOR]

Constraints on neutrino masses are estimated based on future observations of the cosmic microwave background (CMB), which includes the B-mode polarization produced by CMB lensing from the Planck satellite, and the growth rate of cosmic structure from the Euclid redshift survey by using the Markov-Chain Monte-Carlo (MCMC) method. The error in the bound on the total neutrino mass is estimated to be Δ ∑ mν = 0.075 with a 68% confidence level. By using the growth rate rather than the galaxy power spectrum, accurate constraints are obtained, since the growth rate is less influenced by the uncertainty regarding galaxy bias than by the galaxy power spectrum. [ABSTRACT FROM AUTHOR]

We present an overview of a multiwavelength survey of the Shapley Supercluster (SSC; z ∼ 0.05) covering a contiguous area of 260 $h^{-2}_{70}$ Mpc2 including the supercluster core. The project main aim is to quantify the influence of cluster-scale mass assembly on galaxy evolution in one of the most massive structures in the local Universe. The Shapley Supercluster Survey (ShaSS) includes nine Abell clusters (A3552, A3554, A3556, A3558, A3559, A3560, A3562, AS0724, AS0726) and two poor clusters (SC1327−312, SC1329−313) showing evidence of cluster–cluster interactions. Optical (ugri) and near-infrared (K) imaging acquired with VLT Survey Telescope and Visible and Infrared Survey Telescope for Astronomy allow us to study the galaxy population down to m⋆ + 6 at the supercluster redshift. A dedicated spectroscopic survey with AAOmega on the Anglo-Australian Telescope provides a magnitude-limited sample of supercluster members with 80 per cent completeness at ∼m⋆ + 3. We derive the galaxy density across the whole area, demonstrating that all structures within this area are embedded in a single network of clusters, groups and filaments. The stellar mass density in the core of the SSC is always higher than 9 × 109 M⊙ Mpc−3, which is ∼40× the cosmic stellar mass density for galaxies in the local Universe. We find a new filamentary structure (∼7 Mpc long in projection) connecting the SSC core to the cluster A3559, as well as previously unidentified density peaks. We perform a weak-lensing analysis of the central 1 deg2 field of the survey obtaining for the central cluster A3558 a mass of $M_{500}=7.63_{-3.40}^{+3.88}\times 10^{14}\,\mathrm{M}_{\odot }$, in agreement with X-ray based estimates. [ABSTRACT FROM AUTHOR]

We derive peculiar velocities for the 6dF Galaxy Survey (6dFGS) and describe the velocity field of the nearby (z < 0.055) Southern hemisphere. The survey comprises 8885 galaxies for which we have previously reported Fundamental Plane data. We obtain peculiar velocity probability distributions for the redshift-space positions of each of these galaxies using a Bayesian approach. Accounting for selection bias, we find that the logarithmic distance uncertainty is 0.11 dex, corresponding to 26 per cent in linear distance. We use adaptive kernel smoothing to map the observed 6dFGS velocity field out to cz ∼ 16 000 km s−1, and compare this to the predicted velocity fields from the PSCz Survey and the 2MASS Redshift Survey. We find a better fit to the PSCz prediction, although the reduced χ2 for the whole sample is approximately unity for both comparisons. This means that, within the observational uncertainties due to redshift-independent distance errors, observed galaxy velocities and those predicted by the linear approximation from the density field agree. However, we find peculiar velocities that are systematically more positive than model predictions in the direction of the Shapley and Vela superclusters, and systematically more negative than model predictions in the direction of the Pisces-Cetus Supercluster, suggesting contributions from volumes not covered by the models. [ABSTRACT FROM AUTHOR]

We investigate a model derived from bootstrap percolation on a directed random graph with Gaussian in-degree useful in describing the collective behavior of dissociated neuronal networks. By developing a continuous version of the model, we were able to provide accurate values of the critical thresholds and exponents associated with the occurrence of a giant cluster. As a main result, it turns out that the values of the exponents calculated over a numerical accessible range covering more than two orders of magnitude below the critical point exhibit a slight dependence upon the connectivity of the graph. [ABSTRACT FROM AUTHOR]

The presence of superclusters based on Cu-centered icosahedra was studied via classical molecular dynamics simulations in Cu64Zr36 metallic glass. Medium-range order was identified by determining the nearest-neighbor histogram and bond-angle distribution of superclusters. A heterogeneous distribution of icosahedra was observed while other common cluster types are distributed homogeneously. The degree of superclustering, as quantified by the number of cap-sharing bonds per icosahedron, was found to depend only on the icosahedron fraction, irrespective of thermal history. This is further supported by a long-time annealing in the supercooled liquid regime, where the number of icosahedra significantly increases and the formation of superclusters is consequently enhanced. While distorted icosahedra are not found in the vicinity of full icosahedra, the Zr-centered (0 0 12 4) clusters show a high spatial correlation to Cu-centered icosahedra. This is indicative of early stages of crystallization into a Cu2Zr Laves phase. [ABSTRACT FROM AUTHOR]

We present the results of our study of the peculiar motions for 41 galaxy clusters and groups in the regions of the Hercules and Leo superclusters (0.027 < z < 0.045). For this purpose, based on SDSS (Data Release 8) data, we compiled a sample of early-type galaxies in the investigated clusters and groups, constructed their fundamental planes (FPs), and determined independent distances and peculiar velocities. The Hubble law between the radial velocities galaxy clusters and the distances derived from the FPs holds for the rich Hercules supercluster as a whole. At the same time, however, significant peculiar motions along the line of sight with rms deviations of 736 ± 50 and 584 ± 50 km s are observed within this supercluster and in its immediate neighborhood. In the poor Leo supercluster, the rms deviation is also large, 625 ± 70 km s. Its Hubble diagram exhibits the approach of galaxy clusters and groups along the line of sight relative to the most massive cluster A1185. In the immediate neighborhood of the Leo supercluster (virtually in its field), the rms deviation of the peculiar velocities is minimal, 287 ± 60 km s. [ABSTRACT FROM AUTHOR]

A few experiments have detected icosahedral superclusters in undercooled liquids. These superclusters survive above the crystal melting temperature Tm because all their surface atoms have the same fusion heat as their core atoms, and are melted by liquid homogeneous and heterogeneous nucleation in their core, depending on superheating time and temperature. They act as heterogeneous growth nuclei of crystallized phase at a temperature Tc of the undercooled melt. They contribute to the critical barrier reduction, which becomes smaller than that of crystals containing the same atom number n. After strong superheating, the undercooling rate is still limited because the nucleation of 13-atom superclusters always reduces this barrier, and increases Tc above a homogeneous nucleation temperature equal to Tm/3 in liquid elements. After weak superheating, the most stable superclusters containing n = 13, 55, 147, 309 and 561 atoms survive or melt and determine Tc during undercooling, depending on n and sample volume. The experimental nucleation temperatures Tc of 32 liquid elements and the supercluster melting temperatures are predicted with sample volumes varying by 18 orders of magnitude. The classical Gibbs free energy change is used, adding an enthalpy saving related to the Laplace pressure change associated with supercluster formation, which is quantified for n = 13 and 55. [ABSTRACT FROM AUTHOR]

Context. To understand the formation, evolution, and present-day properties of the cosmic web we need to study it at low and high redshifts. Aims. We trace the cosmic web at redshifts that range from 1.0 ⩽ z ⩽ 1.8 by using the quasar (QSO) data from the SDSS DR7 QSO catalogue. Methods. We apply a friend-of-friend algorithm to the quasar and random catalogues to determine systems at a series of linking length and analyse richness and sizes of these systems. Results. At the linking lengths l ⩽ 30 h-1 Mpc, the number of quasar systems is larger than the number of systems detected in random catalogues, and the 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, ≈10-7 (h-1 Mpc)-3, is close to the mean space density of local rich superclusters. At intermediate linking lengths (40 ⩽ l ⩽ 70 h-1 Mpc), 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. The percolating system, which penetrate the whole sample volume appears in a quasar sample at a smaller linking length than in random samples (85 h-1 Mpc). At the linking length 70 h-1 Mpc, the richest systems of quasars have diameters exceeding 500 h-1 Mpc. Quasar luminosities in systems are not correlated with the system richness. Conclusions. Quasar system catalogues in our web pages and at the Strasbourg Astronomical Data Center (CDS) serve as a database for searching superclusters of galaxies and for tracing the cosmic web at high redshifts. [ABSTRACT FROM AUTHOR]

Using two volume-limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 10 (SDSS DR10), we investigate the dependence of the clustering properties of galaxies on stellar velocity dispersion by cluster analysis. It is found that in the luminous volume-limited Main galaxy sample, except at r=1.2, richer and larger systems can be more easily formed in the large stellar velocity dispersion subsample, while in the faint volume-limited Main galaxy sample, at r≥0.9, an opposite trend is observed. According to statistical analyses of the multiplicity functions, we conclude in two volume-limited Main galaxy samples: small stellar velocity dispersion galaxies preferentially form isolated galaxies, close pairs and small group, while large stellar velocity dispersion galaxies preferentially inhabit the dense groups and clusters. However, we note the difference between two volume-limited Main galaxy samples: in the faint volume-limited Main galaxy sample, at r≥0.9, the small stellar velocity dispersion subsample has a higher proportion of galaxies in superclusters ( n≥200) than the large stellar velocity dispersion subsample. [ABSTRACT FROM AUTHOR]

In this study, we investigate the formation and evolution mechanisms of the brightest cluster galaxies (BCGs) over cosmic time. At high redshift (z ∼ 0.9), we selected BCGs and most massive cluster galaxies (MMCGs) from the Cl1604 supercluster and compared them to low-redshift (z ∼ 0.1) counterparts drawn from the MCXC meta-catalogue, supplemented by Sloan Digital Sky Survey imaging and spectroscopy. We observed striking differences in the morphological, colour, spectral, and stellar mass properties of the BCGs/MMCGs in the two samples. High-redshift BCGs/MMCGs were, in many cases, star-forming, late-type galaxies, with blue broad-band colours, properties largely absent amongst the low-redshift BCGs/MMCGs. The stellar mass of BCGs was found to increase by an average factor of 2.51 ± 0.71 from z ∼ 0.9 to z ∼ 0.1. Through this and other comparisons, we conclude that a combination of major merging (mainly wet or mixed) and in situ star formation are the main mechanisms which build stellar mass in BCGs/MMCGs. The stellar mass growth of the BCGs/MMCGs also appears to grow in lockstep with both the stellar baryonic and total mass of the cluster. Additionally, BCGs/MMCGs were found to grow in size, on average, a factor of ∼3, while their average Sérsic index increased by ∼0.45 from z ∼ 0.9 to z ∼ 0.1, also supporting a scenario involving major merging, though some adiabatic expansion is required. These observational results are compared to both models and simulations to further explore the implications on processes which shape and evolve BCGs/MMCGs over the past ∼7 Gyr. [ABSTRACT FROM AUTHOR]

We have used 4000 Å break and HδA indices in combination with SFR/M* derived from emission line flux measurements to constrain the recent star formation histories of galaxies with stellar masses in the range 108–1010 M⊙. The fraction of the total SFR density in galaxies with ongoing bursts is a strong function of stellar mass, declining from 0.85 at a stellar mass of 108 M⊙ to 0.25 for galaxies with M* ∼ 1010 M⊙. Low-mass galaxies are not all young. The distribution of half-mass formation times for galaxies with stellar masses less than 109 M⊙ is broad, spanning the range 1–10 Gyr. The peak-to-trough variation in star formation rate among the bursting population ranges lies in the range 10–25. In low-mass galaxies, the average duration of the bursts is comparable to the dynamical time of the galaxy. Galaxy structure is correlated with estimated burst mass fraction, but in different ways in low- and high-mass galaxies. High-mass galaxies with large burst mass fractions are more centrally concentrated, indicating that bulge formation is at work. In low-mass galaxies, stellar surface densities μ* decrease as a function of Fburst. These results are in good agreement with the observational predictions of Teyssier et al. and lend further credence to the idea that the cuspy halo problem can be solved by energy input from multiple starbursts over the lifetime of the galaxy. We note that there is no compelling evidence for initial mass function variations in the population of star-forming galaxies in the local Universe. [ABSTRACT FROM AUTHOR]

We study the surface brightness profiles of disc galaxies in the 3.6 μm images from the Spitzer Survey of Stellar Structure in Galaxies (S4G) and Ks-band images from the Near-Infrared S0-Sa galaxy Survey (NIRS0S). We particularly connect properties of single exponential (type I), downbending double exponential (type II), and upbending double exponential (type III) disc profile types, to structural components of galaxies by using detailed morphological classifications, and size measurements of rings and lenses. We also study how the local environment of the galaxies affects the profile types by calculating parameters describing the environmental density and the tidal interaction strength. We find that in majority of type II profiles the break radius is connected with structural components such as rings, lenses, and spirals. The exponential disc sections of all three profile types, when considered separately, follow the disc scaling relations. However, the outer discs of type II, and the inner discs of type III, are similar in scalelength to the single exponential discs. Although the different profile types have similar mean environmental parameters, the scalelengths of the type III profiles show a positive correlation with the tidal interaction strength. [ABSTRACT FROM AUTHOR]

A modification of the Press-Schechter model for the mass function of the dark halos, whose population develops in the presence of a supercluster or a cosmological void, is proposed. The large-scale structure is specified as a set of statistical constraints in the form of linear functionals that are applied to the initial overdensity field. The parameters and values of these functionals are related to properties of the large-scale structure: its mean density, spatial scales, and shape. The model is applied to the simple case of a spherically symmetric background structure to demonstrate a procedure for recovering these parameters by fitting the halo mass function. [ABSTRACT FROM AUTHOR]

Highlights: [•] The rotation about the Galactic center of open clusters is studied. [•] The minor effects caused by the Lin–Shu density waves are taken into account. [•] The one-armed spiral mode is the dominant mode of oscillation in the solar vicinity. [•] The spirals do not represent small deviations of the density from a basic axisymmetric distribution. [ABSTRACT FROM AUTHOR]

The ability to manipulate matter to create non-conventional structures is one of the key issues of material science. The understanding of assembling mechanism at the nanoscale allows us to engineer new nanomaterials, with physical properties intimately depending on their structure. This paper describes new strategies to obtain and characterise metal nanostructures via the combination of a top-down method, such as electron beam lithography, and a bottom-up technique, such as the chemical electroless deposition. We realised silver nanoparticle aggregates within well-defined patterned holes created by electron beam lithography on silicon substrates. The quality characteristics of the nanoaggregates were verified by using scanning electron microscopy and atomic force microscopy imaging. Moreover, we compared the experimental findings to molecular dynamics simulations of nanoparticles growth. We observed a very high dependence of the structure characteristics on the pattern nanowell aspect ratio. We found that high-quality metal nanostructures may be obtained in patterns with well aspect ratio close to one, corresponding to a maximum diameter of 50 nm, a limit above which the fabricated structures become less regular and discontinuous. When regular shapes and sizes are necessary, as in nanophotonics, these results suggest the pattern characteristics to obtain isolated, uniform and reproducible metal nanospheres. [ABSTRACT FROM AUTHOR]

The new revolution in materials science is being driven by our ability to manipulate matter at the molecular level to create structures with novel functions and properties. The aim of this paper is to explore new strategies to obtain plasmonic metal nanostructures through the combination of a top down method, that is electron beam lithography, and a bottom up technique, that is the chemical electroless deposition. This technique allows a tight control over the shape and size of bi- and three-dimensional metal patterns at the nano scale. The resulting nanostructures can be used as constituents of Surface Enhanced Raman Spectroscopy (SERS) substrates, where the electromagnetic field is strongly amplified. Our results indicate that, in electroless growth, high quality metal nanostructures with sizes below 50 nm may be easily obtained. These findings were explained within the framework of a diffusion limited aggregation (DLA) model, that is a simulation model that makes it possible to decipher, at an atomic level, the rules governing the evolution of the growth front; moreover, we give a description of the physical mechanisms of growth at a basic level. In the discussion, we show how these findings can be utilized to fabricate dimers of silver nanospheres where the size and shape of those spheres is controlled with extreme precision and can be used for very large area SERS substrates and nano-optics, for single molecule detection. [ABSTRACT FROM AUTHOR]

We present an analytic formula for the supercluster mass function, which is constructed by modifying the extended Zel'dovich model for the halo mass function. The formula has two characteristic parameters whose best-fit values are determined by fitting to the numerical results from N-body simulations for the standard ΛCDM cosmology. The parameters are found to be independent of redshifts and robust against variation of the key cosmological parameters. Under the assumption that the same formula for the supercluster mass function is valid for non-standard cosmological models, we show that the relative abundance of the rich superclusters should be a powerful indicator of any deviation of the real universe from the prediction of the standard ΛCDM model. [ABSTRACT FROM AUTHOR]

Context. The Galactic bulge is a massive, old component of the Milky Way. It is known to host a bar, and it has recently been demonstrated to have a pronounced boxy/peanut structure in its outer region. Several independent studies suggest the presence of more than one stellar populations in the bulge, with different origins and a relative fraction changing across the bulge area. Aims. This is the first of a series of papers presenting the results of the Giraffe Inner Bulge Survey, carried out at the ESO-VLT with the multifibre spectrograph FLAMES. Spectra of ~5000 red clump giants in 24 bulge fields have been obtained at resolution R = 6500, in the infrared Calcium triplet wavelength region at ~8500 Å. They are used to derive radial velocities and metallicities, based on new calibration specifically devised for this project. Radial velocities for another ~1200 bulge red clump giants, obtained from similar archive data, have been added to the sample. Higher resolution spectra have been obtained for ~450 additional stars at latitude b = -3.5, with the aim of investigating chemical abundance patterns variations with longitude, across the inner bulge. In total we present here radial velocities for 6392 red clump stars. Methods. We present here the target selection criteria, observing strategy and the catalog with radial velocity measurements for all the target stars. Results. We derive a radial velocity, and velocity dispersion map of the Milky Way bulge, useful to be compared with similar maps of external bulges, and to infer the expected velocities and dispersion at any line of sight. The K-type giants kinematics is consistent with the cylindrical rotation pattern of M-giants from the BRAVA survey. Our sample enables to extend this result to latitude b = -2, closer to the Galactic plane than probed by previous surveys. Finally, we find strong evidence for a velocity dispersion peak at (0, -1) and (0, -2), possibily indicative of a high density peak in the central ~250 pc of the bulge. [ABSTRACT FROM AUTHOR]