Search

We study the radial velocity dependence in the spatial orientations of 10 562 spiral galaxies that have radial velocity <5000 km s−1. The inclination angle and intrinsic flatness of galaxy are used to covert two-dimensional given parameters into three-dimensional spin vectors of the galaxy. We have performed Kolmogorov–Smirnov, Kuiper and Fourier tests in order to examine non-random effects in the expected isotropic distributions. The galaxies that have radial velocities 1500 to 2000 and 3000 to 3500 km s−1 show preferred alignments in both the two- and three-dimensional analysis. The possible explanations of the results will be discussed. [ABSTRACT FROM AUTHOR]

With the help of a statistical parameter derived from optical spectra, we show that the current star formation rate of a galaxy, falling into a cluster along a supercluster filament, is likely to undergo a sudden enhancement before the galaxy reaches the virial radius of the cluster. From a sample of 52 supercluster-scale filaments of galaxies joining a pair of rich clusters of galaxies within the two-degree Field Redshift Survey region, we find a significant enhancement of star formation, within a narrow range between ∼2 and of the centre of the cluster into which the galaxy is falling. This burst of star formation is almost exclusively seen in the fainter dwarf galaxies . The relative position of the peak does not depend on whether the galaxy is a member of a group or not, but non-group galaxies have on average a higher rate of star formation immediately before falling into a cluster. From the various trends, we conclude that the predominant process responsible for this rapid burst is the close interaction with other galaxies falling into the cluster along the same filament, if the interaction occurs before the gas reservoir of the galaxy gets stripped off due to the interaction with the intracluster medium. [ABSTRACT FROM AUTHOR]

Abstract: Death receptors induce apoptosis through either the Type I or II pathway. In Type I cells, the initiator caspase-8 directly activates effector caspases such as caspase-3, whereas in Type II cells, the death signal is amplified through mitochondria thereby activating effector caspases causing cell death. Recently, there have been advances in elucidating the early events in the CD95 signaling pathways and how post-translational modifications regulate CD95 signaling. This review will focus on recent insights into the mechanisms of the two different types of CD95 signaling pathways, and will introduce miRNAs as regulators of death receptor signaling. [Copyright &y& Elsevier]

Abstract: A growing neutrino mass can stop the dynamical evolution of a dark energy scalar field, thus explaining the “why now” problem. We show that such models lead to a substantial neutrino clustering on the scales of superclusters. Non-linear neutrino lumps form at redshift and could partially drag the clustering of dark matter. If observed, large scale non-linear structures could be an indication for a new attractive “cosmon force” stronger than gravity. [Copyright &y& Elsevier]

In this Letter, we investigate the very large-scale environments of cluster-scale triplets of type 1 Seyfert galaxies, lower luminosity counterparts of quasars, detected at z < 0.2 in the fourth Data Release of the Sloan Digital Sky Survey. The search for cluster scale triplets (object-object separations ) in a combined sample of Seyferts and quasars resulted in only 7 triplets, 3 of which are at z < 0.2. We investigated their environments and found a strong association of z < 0.2 triplets with the richest central parts of superclusters. In two out of three cases, the members of the triplets have been found on the periphery of an extremelly rich galaxy cluster (Abell class 2 and 3). The third triplet also appears associated with a very rich cluster of galaxies but on a somewhat larger scale. Nevertheless, on a small scale, it is still associated with a cluster but of lesser richness. These results suggest that triplets of type 1 Seyfert galaxies at low redshifts are excellent tracers of very rich clusters. Following these results we conclude that triplets of quasars, bright counterparts of type 1 Seyfert galaxies, may be the most successful means of finding distant, very rich, galaxy clusters. [ABSTRACT FROM AUTHOR]

To study the local Hubble flow, we have run constrained dark matter (DM) simulations of the Local Group (LG) in the concordance Λ cold dark matter (CDM) and open cold dark matter (OCDM) cosmologies, with identical cosmological parameters apart from the Λ term. The simulations were performed within a computational box of centred on the LG. The initial conditions were constrained by the observed peculiar velocities of galaxies and positions of X-ray nearby clusters of galaxies. The simulations faithfully reproduce the nearby large-scale structure, and in particular the Local Supercluster and the Virgo cluster. LG-like objects have been selected from the DM haloes so as to closely resemble the dynamical properties of the LG. Both the ΛCDM and OCDM simulations show very similar local Hubble flow around the LG-like objects. It follows that, contrary to recent statements, the dark energy (DE) does not manifest itself in the local dynamics. [ABSTRACT FROM AUTHOR]

We present a high-resolution dark matter reconstruction of the Abell 901/902 supercluster from a weak lensing analysis of the Hubble Space Telescope STAGES survey. We detect the four main structures of the supercluster at high significance, resolving substructure within and between the clusters. We find that the distribution of dark matter is well traced by the cluster galaxies, with the brightest cluster galaxies marking out the strongest peaks in the dark matter distribution. We also find a significant extension of the dark matter distribution of Abell 901a in the direction of an infalling X-ray group Abell 901α. We present mass, mass-to-light and mass-to-stellar mass ratio measurements of the structures and substructures that we detect. We find no evidence for variation of the mass-to-light and mass-to-stellar mass ratio between the different clusters. We compare our space-based lensing analysis with an earlier ground-based lensing analysis of the supercluster to demonstrate the importance of space-based imaging for future weak lensing dark matter ‘observations’. [ABSTRACT FROM AUTHOR]

The article reports on the study of the performance of the 10,240-processor supercluster and supercomputer called "Columbia" in the Ames Research Center of the National Aeronautics and Space Administration (NASA) in Moffett Field, California. The study examines the performance characteristics of Columbia's production subclusters with 512 to 2048 processors. It also measures the floating-point performance, memory bandwidth, and message passing communication speeds of the Columbia. The study uses the HPC challenge benchmarks, NASA Advanced Supercomputing (NAS) parallel benchmarks, and the computational fluid dynamics application in the performance evaluation of the Columbia.

The sample of nearby LIRGs and ULIRGs for which dense molecular gas tracers have been measured is building up, allowing for the study of the physical and chemical properties of the gas in the variety of objects in which the most intense star formation and/or AGN activity in the local universe is taking place. This characterisation is essential to understand the processes involved, discard others and help to interpret the powerful starbursts and AGNs at high redshift that are currently being discovered and that will routinely be mapped by ALMA. We have studied the properties of the dense molecular gas in a sample of 17 nearby LIRGs and ULIRGs through millimeter observations of several molecules (HCO+, HCN, CN, HNC and CS) that trace different physical and chemical conditions of the dense gas in these extreme objects. In this paper we present the results of our HCO+ and HCN observations. We conclude that the very large range of measured line luminosity ratios for these two molecules severely questions the use of a unique molecular tracer to derive the dense gas mass in these galaxies. [ABSTRACT FROM AUTHOR]

The characteristics of ionized and H i gas in the peculiar star/cluster complex in NGC 6946, obtained with the 6-m telescope (BTA) Special Astrophysical Observatory Russian Academy of Sciences (RAS), the Gemini North telescope, and the Westerbork Synthesis Radio Telescope, are presented. The complex is unusual as hosting a super star cluster, the most massive known in an apparently non-interacting giant galaxy. It contains a number of smaller clusters and is bordered by a sharp C-shaped rim. We found that the complex is additionally unusual in having peculiar gas kinematics. The velocity field of the ionized gas reveals a deep oval minimum, ∼300 pc in size, centred 7 arcsec east of the supercluster. The Vr of the ionized gas in the dip centre is 100 km s−1 lower than in its surroundings, and emission lines within the dip appear to be shock-excited. This dip is near the centre of an H i hole and a semi-ring of H ii regions. The H i (and less certainly, H ii) velocity fields reveal expansion, with the velocity reaching ∼30 km s−1 at a distance about 300 pc from the centre of expansion, which is near the deep minimum position. The superstar cluster is at the western rim of the minimum. The sharp western rim of the whole complex is plausibly a manifestation of a regular dust arc along the complex edge. Different hypotheses about the complex and the Vr depression's origins are discussed, including a high-velocity H i cloud/dark minihalo impact, a blue compact dwarf galaxy merging, and a gas outflow due to release of energy from the supercluster stars. [ABSTRACT FROM AUTHOR]

We apply the Delaunay Tessellation Field Estimator (DTFE) to reconstruct and analyse the matter distribution and cosmic velocity flows in the local Universe on the basis of the PSC z galaxy survey. The prime objective of this study is the production of optimal resolution 3D maps of the volume-weighted velocity and density fields throughout the nearby universe, the basis for a detailed study of the structure and dynamics of the cosmic web at each level probed by underlying galaxy sample. Fully volume-covering 3D maps of the density and (volume-weighted) velocity fields in the cosmic vicinity, out to a distance of , are presented. Based on the Voronoi and Delaunay tessellation defined by the spatial galaxy sample, DTFE involves the estimate of density values on the basis of the volume of the related Delaunay tetrahedra and the subsequent use of the Delaunay tessellation as natural multidimensional (linear) interpolation grid for the corresponding density and velocity fields throughout the sample volume. The linearized model of the spatial galaxy distribution and the corresponding peculiar velocities of the PSC z galaxy sample, produced by Branchini et al., forms the input sample for the DTFE study. The DTFE maps reproduce the high-density supercluster regions in optimal detail, both their internal structure as well as their elongated or flattened shape. The corresponding velocity flows trace the bulk and shear flows marking the region extending from the Pisces–Perseus supercluster, via the Local Superclusters, towards the Hydra–Centaurus and the Shapley concentration. The most outstanding and unique feature of the DTFE maps is the sharply defined radial outflow regions in and around underdense voids, marking the dynamical importance of voids in the local Universe. The maximum expansion rate of voids defines a sharp cut-off in the DTFE velocity divergence probability distribution function. We found that on the basis of this cut-off DTFE manages to consistently reproduce the value of Ωm≈ 0.35 underlying the linearized velocity data set. [ABSTRACT FROM AUTHOR]

The evolution of present-day fossil galaxy groups is studied in the Millennium simulation. Using the corresponding Millennium gas simulation and semi-analytic galaxy catalogues, we select fossil groups at redshift zero according to the conventional observational criteria, and trace the haloes corresponding to these groups backwards in time, extracting the associated dark matter, gas and galaxy properties. The space density of the fossils from this study is remarkably close to the observed estimates and various possibilities for the remaining discrepancy are discussed. The fraction of X-ray bright systems which are fossils appears to be in reasonable agreement with observations, and the simulations predict that fossil systems will be found in significant numbers (3–4 per cent of the population) even in quite rich clusters. We find that fossils assemble a higher fraction of their mass at high redshifts, compared to non-fossil groups, with the ratio of the currently assembled halo mass to final mass, at any epoch, being about 10–20 per cent higher for fossils. This supports the paradigm whereby fossils represent undisturbed, early-forming systems in which large galaxies have merged to form a single dominant elliptical. [ABSTRACT FROM AUTHOR]

We present two non-parametric deprojection methods aimed at recovering the three-dimensional density and temperature profiles of galaxy clusters from spatially resolved thermal Sunyaev–Zeldovich (tSZ) and X-ray surface brightness maps, thus avoiding the use of X-ray spectroscopic data. In both methods, the cluster is assumed spherically symmetric and modelled with an onion-skin structure. The first method follows a direct geometrical approach, in which the deprojection is performed independently for the tSZ and X-ray images, and the resulting profiles are then combined in order to extract density and temperature. The second method is based on the maximization of a single joint (tSZ and X-ray) likelihood function. This allows us to simultaneously fit the two signals by following a Monte Carlo Markov Chain (MCMC) approach. These techniques are tested against both an idealized spherical β-model cluster and a set of clusters extracted from cosmological hydrodynamical simulations with and without instrumental noise. In the first case, the quality of reconstruction is excellent and demonstrates that such methods do not suffer from any intrinsic bias. As for the application to simulations, we projected each cluster along the three orthogonal directions defined by the principal axes of the momentum of inertia tensor. This enables us to check any bias in the deprojection associated to the cluster elongation along the line of sight. After averaging over all the three projection directions, we find an overall good reconstruction, with a small (≲10 per cent) overestimate of the gas density profile. This turns into a comparable overestimate of the gas mass within the virial radius, which we ascribe to the presence of residual gas clumping. Apart from this small bias, the reconstruction has an intrinsic scatter of about 5 per cent, which is dominated by gas clumpiness. Cluster elongation along the line of sight biases the deprojected temperature profile upwards at and downwards at larger radii. A comparable bias is also found in the deprojected temperature profile. Overall, this turns into a systematic underestimate of the gas mass, up to 10 per cent. We point out that our recovered temperature profiles are much closer to the mass-weighted profiles than those obtained from the X-ray spectroscopic-like temperature. These results confirm the potentiality of combining tSZ and X-ray imaging observations to the study of the thermal structure of the intra-cluster medium out to large cluster-centric distances. [ABSTRACT FROM AUTHOR]

We present new optical spectroscopy for galaxies in the Shapley supercluster (and 198 supplementary galaxies), obtained from 8-h integrations with the AAOmega facility at the Anglo-Australian Telescope. We describe the observations and measurements of central velocity dispersion σ, emission-line equivalent widths and absorption-line indices. The distinguishing characteristic of the survey is its coverage of a very wide baseline in velocity dispersion (90 per cent range ), while achieving high signal-to-noise ratio throughout (median 60 Å−1 at 5000 Å). The data quality will enable estimates of Balmer-line ages to better than 20 per cent precision even for the faintest galaxies in the sample. Significant emission at Hα was detected in ∼30 per cent of the supercluster galaxies, including ∼20 per cent of red-sequence members. Using line-ratio diagnostics, we find that the emission is LINER (low ionization nuclear emission region) like at high luminosity, but driven by star formation in low-luminosity galaxies. To characterize the absorption lines, we use the classical Lick indices in the spectral range 4000–5200 Å. We introduce a new method for applying resolution corrections to the line-strength indices. We define a subset of galaxies with very low emission contamination, based on the Hα line, and fit the index–σ relations for this subset. The relations show the continuation of the familiar trends for giant galaxies into the low-luminosity regime, with little change in slope for most indices. Comparing the index–σ slopes against predictions from single-burst stellar population models, we infer the scaling relations of age, total metallicity, [ Z/H], and α-element abundance ratio, [α/Fe]. To reproduce the observed index–σ slopes, all three parameters must increase significantly with increasing velocity dispersion. Specifically, we recover and (where the second error reflects systematic effects), derived over a decade baseline in velocity dispersion, . The equivalent slopes for the subset of galaxies with are similar for age and Z/H. For α/Fe, a steeper slope is recovered for the high-σ subset, . The recovered age–σ relation is shown to be consistent with the observed evolution in the giant-to-dwarf galaxy ratio in clusters at redshifts . In a companion paper, we determine the age, [ Z/H] and [α/Fe] for individual galaxies, and investigate in detail the distribution of galaxy properties at fixed velocity dispersion. [ABSTRACT FROM AUTHOR]

We consider the main population of cosmic voids in a heirarchical clustering model. Based on the Press-Schechter formalism modified for regions in the Universe with reduced or enhanced matter densities, we construct the mass functions for gravitationally bound objects of dark matter occupying voids or superclusters. We show that the halo mass functions in voids and superclusters differ substantially. In particular, the spatial density of massive ( M ∼ 1012 M ⊙) halos is appreciably lower in voids than in superclusters, with the difference in the mass functions being greater for larger masses. According to our computations, an appreciable fraction of the mass of matter in voids should be preserved to the present epoch in the form of primordial gravitationally bound objects (POs) with modest masses (to 10% for M PO < 109 M ⊙) keeping baryons. These primordial objects represent “primary blocks” in the heirarchical clustering model. We argue that the oldest globular clusters in the central regions of massive galaxies are the stellar remnants of these primordial objects: they can form in molecular clouds in these objects, only later being captured in the central regions of massive galaxies in the process of gravitational clustering. Primordial objects in voids can be observed as weak dwarf galaxies or Lyα absorption systems. [ABSTRACT FROM AUTHOR]

We present XMM data for the supercluster A901/2, at , which is combined with deep imaging and 17-band photometric redshifts (from the COMBO-17 survey), two degree field (2dF) spectra and Spitzer 24 μm data, to identify active galactic nuclei (AGN) in the supercluster. The 90 ksec XMM image contains 139 point sources, of which 11 are identified as supercluster AGN with . The host galaxies have and only two of eight sources with spectra could have been identified as AGN by the detected optical emission lines. Using a large sample of 795 supercluster galaxies, we define control samples of massive galaxies with no detected AGN. The local environments of the AGN and control samples differ at ≳98 per cent significance. The AGN host galaxies lie predominantly in areas of moderate projected galaxy density and with more local blue galaxies than the control sample, with the exception of one very bright type I AGN very near the centre of a cluster. These environments are similar to, but not limited to, cluster outskirts and blue groups. Despite the large number of potential host galaxies, no AGN are found in regions with the highest galaxy density (excluding some cluster cores where emission from the intra-cluster medium obscures moderate luminosity AGN). AGN are also absent from the areas with lowest galaxy density. We conclude that the prevalence of cluster AGN is linked to their environment. [ABSTRACT FROM AUTHOR]

We analyse the first publicly released deep field of the UK Infrared Deep Sky Survey (UKIDSS) Deep eXtragalactic Survey to identify candidate galaxy overdensities at across ∼1 deg2 in the ELAIS-N1 field. Using and colours, we identify and spectroscopically follow up five candidate structures with Gemini/Gemini Multi-Object Spectrograph and confirm that they are all true overdensities with between five and 19 members each. Surprisingly, all five structures lie in a narrow redshift range at , although they are spread across 30 Mpc on the sky. We also find a more distant overdensity at in one of the spectroscopic survey regions. These five overdense regions lying in a narrow redshift range indicate the presence of a supercluster in this field and by comparing with mock cluster catalogues from N-body simulations we discuss the likely properties of this structure. Overall, we show that the properties of this supercluster are similar to the well-studied Shapley and Hercules superclusters at lower redshift. [ABSTRACT FROM AUTHOR]

As a concluding paper in this series, we present an analysis of the spatial orientations of galaxies in seven Abell clusters of BM type II and compare the results with previous works. Four BM type II clusters (A1767, A1809, A2554, A2721) show a similar preferred alignment: spin vectors of galaxies tend to lie in the local supercluster plane and the projections of the spin vector tend to be oriented perpendicular with respect to the Virgo cluster centre. A preferred alignment of galaxies in cluster A2554 is noticed in both the two- and three-dimensional analyses. In a comparison with previous work, we noticed a systematic change (with distance, radial velocity, morphology and magnitude) in the galaxy alignments from early-type (BM I) to late-type (BM III) clusters. Possible explanations of these systematic changes will be discussed. [ABSTRACT FROM AUTHOR]

We have searched for nearby dwarf galaxies in 27 northern groups with characteristic distances 8–15 Mpc based on the Second Palomar Sky Survey prints. In a total area of about 2000 square degrees, we have found 90 low-surface-brightness objects, more than 60% of which are absent from known catalogs and lists. We have classified most of these objects (∼80%) as irregular dwarf systems. The first 21-cm line observations of the new objects with the 100-m Effelsberg radio telescope showed that the typical linear diameters (1–2 kpc), internal motions (∼30 km s−1), and hydrogen masses (∼2 × 107 M ⊙) of the new galaxies correspond to those expected for the dwarf population of nearby groups. [ABSTRACT FROM AUTHOR]

We present a morphological study of galaxies in the A901/902 supercluster from the COMBO-17 survey. A total of 570 galaxies with photometric redshifts in the range are visually classified by three independent classifiers to . These morphological classifications are compared to local galaxy density, distance from the nearest cluster centre, local surface mass density from weak lensing and photometric classification. At high local galaxy densities a classical morphology–density relation is found. A correlation is also found between morphology and local projected surface mass density, but no trend is observed with distance to the nearest cluster. This supports the finding that local environment is more important to galaxy morphology than global cluster properties. The breakdown of the morphological catalogue by colour shows a dominance of blue galaxies in the galaxies displaying late-type morphologies and a corresponding dominance of red galaxies in the early-type population. Using the 17-band photometry from COMBO-17, we further split the supercluster red sequence into old passive galaxies and galaxies with young stars and dust. We find that the dusty star-forming population describes an intermediate morphological group between late- and early-type galaxies, supporting the hypothesis that field and group spiral galaxies are transformed into S0s and, perhaps, ellipticals during cluster infall. [ABSTRACT FROM AUTHOR]

We report a discovery of possible large-scale structures around the RDCS J1252.9−2927 cluster at based on photometric redshifts. We carried out multiband wide-field imaging with Suprime-Cam on the Subaru Telescope and WFCAM on the United Kingdom Infrared Telescope (UKIRT). Our data cover an approximately field in and K bands. We apply a photometric redshift technique to extract galaxies at or near the cluster redshift. The distribution of photo- z selected galaxies reveals clumpy structures surrounding the central cluster. It seems that there is a large (>20 Mpc) filamentary structure extending in the north-east–south-west direction. We compare the observed structure with an X-ray map and find that two of the four plausible clumps show significant X-ray emissions and one with a marginal detection, which strongly suggests that they are dynamically bound systems. Following the discovery of the possible large-scale structure, we carried out deeper SOFI Ks-band imaging with the New Technology Telescope on four plausible clumps. We construct the optical-to-near-infrared colour–magnitude diagrams of the galaxies in the clumps, and find that the colour–magnitude relation (CMR) of the red galaxies in the clumps is sharply truncated below . Few faint red galaxies are seen in these clumps. This suggests that the CMR first appears at the bright magnitudes and it extends to the fainter magnitudes with time, which is consistent with the ‘downsizing’ picture. Interestingly, the CMR of the main cluster has previously been shown to have a clear relation down to . This confirms our previous suggestion that the build-up of the CMR is delayed in low-density environments. All in all, we suggest that galaxies follow the ‘environment-dependent downsizing’ evolution. Massive galaxies in high-density environments first stop forming stars and become red. Less massive galaxies in less dense environments become red at later times. Based on a few assumptions, we predict that the brightest tip of the CMR appears at . [ABSTRACT FROM AUTHOR]

We investigate the variation of current star formation in galaxies as a function of distance along three supercluster filaments, each joining pairs of rich clusters, in the Pisces-Cetus supercluster, which is part of the two-degree Field Galaxy Redshift Survey (2dFGRS). We find that even though there is a steady decline in the rate of star formation, as well as in the fraction of star-forming galaxies, as one approaches the core of a cluster at an extremity of such a filament, there is an increased activity of star formation in a narrow distance range between 3 and , which is 1.5–2 times the virial radius of the clusters involved. This peak in star formation is seen to be entirely due to the dwarf galaxies . The position of the peak does not seem to depend on the velocity dispersion of the nearest cluster, undermining the importance of the gravitational effect of the clusters involved. We find that this enhancement in star formation occurs at the same place for galaxies which belong to groups within these filaments, while group members elsewhere in the 2dFGRS do not show this effect. We conclude that the most likely mechanism for this enhanced star formation is galaxy–galaxy harassment, in the crowded infalling region of rich clusters at the extremities of filaments, which induces a burst of star formation in galaxies, before they have been stripped of their gas in the denser cores of clusters. The effects of strangulation in the cores of clusters, as well as excess star formation in the infalling regions along the filaments, are more pronounced in dwarfs since they more vulnerable to the effects of strangulation and harassment than giant galaxies. [ABSTRACT FROM AUTHOR]

Abstract: The Corona Borealis supercluster has been observed with the millimeter and infrared testa grigia observatory (MITO). Here we present the results of the observations together with a comparison with observations performed at 33GHz with the very small array (VSA) interferometer. We have observed in the direction of the supercluster toward a cosmic microwave background (CMB) cold spot previously detected in a VSA temperature map. We claim a weak detection of a faint signal compatible with a SZ effect characterized at most by a comptonization parameter 68% CL. The low level of confidence in the presence of a SZ signal invites us to study this sky region with higher sensitivity and angular resolution experiments such as already planned upgraded versions of VSA and MITO. This is the first millimetric evidence of unknown cluster/diffuse intra-supercluster gas (possibly warm–hot intergalactic medium (WHIM)) interacting, via inverse Compton, scattering with the CMB. [Copyright &y& Elsevier]

The reconstruction of the energy and momentum of isolated electrons in CMS combining tracking and electromagnetic calorimetry information is described. The emphasis is put on primary electrons with transverse momentum below 50 GeV/c. The energy deposited in the electromagnetic calorimeter is measured in clusters of clusters (superclusters) which collect bremsstrahlung photons emitted along the electron trajectory in the tracker volume. The electron tracks are built from seeds in the pixel detector found via a cluster-driven pixel hit matching algorithm, followed by a reconstruction of trajectories in the silicon strip tracker with a Gaussian sum filter. Electrons are classified using observables sensitive to the pattern of bremsstrahlung emission and electromagnetic showering in the tracker material. Energy scale corrections depending on the electron class are applied to the supercluster and estimates of associated errors are obtained. The electron energy is deduced from a weighted combination of the corrected supercluster energy and tracker momentum measurements. The electron direction is that of the reconstructed electron track at interaction vertex. The pre-selection of isolated electron candidates for physics analysis is described. Class-dependent observables combining tracking and calorimetry information are discussed for electron identification. [ABSTRACT FROM AUTHOR]

The Parkes–MIT–NRAO (PMN) radio survey has been used to generate a quasi all-sky study of Galactic Supernova Remnants (SNRs) at a common frequency of 4.85 GHz ( λ=6 cm). We present flux densities estimated for the sample of 110 Southern Galactic SNRs (up to δ=−65°) observed with the Parkes 64-m radio telescope and an additional sample of 54 from the Northern PMN (up to δ=+64°) survey undertaken with the Green Bank 43-m (20 SNRs) and 91-m (34 SNRs) radio telescopes. Out of this total sample of 164 selected SNRs (representing 71% of the currently 231 known SNRs in the Green catalogue) we consider 138 to provide reliable estimates of flux density and surface brightness distribution. This sub-sample represents those SNRs which fall within carefully chosen selection criteria which minimises the effects of the known problems in establishing reliable fluxes from the PMN survey data. Our selection criteria are based on a judicious restriction of source angular size and telescope beam together with careful evaluation of fluxes on a case by case basis. Direct comparison of our new fluxes with independent literature values gives excellent overall agreement. This gives confidence in the newly derived PMN fluxes when the selection criteria are respected. We find a sharp drop off in the flux densities for Galactic SNRs beyond 4 Jy and then a fairly flat distribution from 5 to 9 Jy, a slight decline and a further flat distribution from 9 to 20 Jy though the numbers of SNR in each Jy bin are low. We also re-visit the contentious Σ– D (radio surface brightness–SNRs diameter) relation to determine a new power law index for a sub-sample of shell type SNRs which yields β=−2.2±0.6. This new evaluation of the Σ– D relation, applied to the restricted sample, provides new distance estimates and their Galactic scale height distribution. We find a peak in the SNR distribution between 7–11 kpc with most restricted to ±100 pc Galactic scale height. [ABSTRACT FROM AUTHOR]

We present an analysis of the chiral property of 667 spiral and barred spiral galaxies in the Local Supercluster (radial velocity <3 000 km s−1). The arms of a galaxy (spiral or barred spiral) can be distinguished according to their orientation (leading or trailing) relative to the direction of the rotation. We use environment of each galaxy as a subsample in order to study the chiral property of galaxies. In addition, equatorial position angle distributions of leading and trailing arm galaxies are studied. We classify our database according as their morphology, diameters, radial velocities, axial ratios and magnitudes. The distribution of trailing and leading arm galaxies in the Local Supercluster is found homogeneous. A significant dominance of either trailing or leading structures is noticed within the Virgo cluster region, suggesting that the aggregation of these structures might have already started there. The rotation axes of the galaxies in the Virgo cluster is found to lie in the equatorial plane. Chirality of galaxies is found strong for the subsamples that showed a random alignment in the equatorial position angle distribution. Possible explanations of the results will be presented. [ABSTRACT FROM AUTHOR]

Using a series of three-dimensional, hydrodynamic simulations on an adaptive grid, we have performed a systematic study on the effect of bubble-induced motions on metallicity profiles in clusters of galaxies. In particular, we have studied the dependence on the bubble size and position, the recurrence times of the bubbles, the way these bubbles are inflated and the underlying cluster profile. We find that in hydrostatic cluster models, the resulting metal distribution is very elongated along the direction of the bubbles. Anisotropies in the cluster or ambient motions are needed if the metal distribution is to be spherical. In order to parametrize the metal transport by bubbles, we compute effective diffusion coefficients. The diffusion coefficients inferred from our simple experiments lie at values of around ∼1029 cm2 s−1 at a radius of 10 kpc. The runs modelled on the Perseus cluster yield diffusion coefficients that agree very well with those inferred from observations. [ABSTRACT FROM AUTHOR]

The astrophysical characteristics of primary cosmic rays (PCRs) and the structure of extensive air showers (EASs) with energy E 0 ≥ 1017 eV are simultaneously analyzed using the Yakutsk EAS array data acquired in the period 1974–2005. Enhanced and reduced particle fluxes are shown to come from the disk of the Supergalaxy (the Local Supercluster of galaxies) at E 0 ≥ 5 × 1018 eV and E 0 ≤ (2−3) × 1018, respectively. The development of air showers with E 0 ≥ (3−5) × 1018 eV differs significantly from that at lower energies. This is interpreted as a manifestation of the possible interaction between extragalactic PCRs and the matter of this spatial structure. [ABSTRACT FROM AUTHOR]

We have derived the mass distribution of galaxy cluster Abell 1689 within of the cluster centre using its strong lensing (SL) effect on 32 background galaxies, which are mapped in altogether 107 multiple images. The multiple images are based on some from the literature with modifications to both include new and exclude some of the original image systems. The cluster profile is explored further out to with weak lensing (WL) shear measurements from the literature. The masses of ∼200 cluster galaxies are measured with the Fundamental Plane (FP) in order to model accurately the small-scale mass structure in the cluster. The cluster galaxies are modelled as elliptical truncated isothermal spheres. The scalings of the truncation radii with the velocity dispersions of galaxies are assumed to match those of: (i) field galaxies; and (ii) theoretical expectations for galaxies in dense environments. The dark matter (DM) component of the cluster is described by either non-singular isothermal ellipsoids (NSIE) or elliptical versions of the universal DM profile (elliptical Navarro, Frenk & White, ENFW). To account for substructure in the DM we allow for two DM haloes. The fitting of a non-singular isothermal sphere (NSIS) to the smooth DM component results in a velocity dispersion of and a core radius of , while a Navarro, Frenk & White (NFW) profile has an r200 of and a concentration of . The total mass profile is well described by either a NSIS profile with and a core radius of , or an NFW profile with and . The errors are assumed to be due to the error in assigning masses to the individual galaxies in the galaxy component. Their small size is due to the very strong constraints imposed by multiple images and the ability of the smooth DM component to adjust to uncertainties in the galaxy masses. The agreement in the total mass profile between this work and that of the literature is better than 1σ at all radii, despite the considerable differences in the methodology used. Using the same image configuration as used in the literature, we obtain a SL model that is superior to some in the literature (rms of 2.7 compared to 3.2 arcsec). This is very surprising considering the larger freedom in the surface mass profile in their grid modelling. The difference is most likely a result of the careful inclusion of the cluster galaxies. Using also WL shear measurements from the literature, we can constrain the profile further out to . The best-fitting parameters change to and for the NSIS profile and and for the NFW profile. [ABSTRACT FROM AUTHOR]

We have redefined group membership of six southern galaxy groups in the local universe (mean ) based on new redshift measurements from our recently acquired Anglo-Australian Telescope 2dF spectra. For each group, we investigate member galaxy kinematics, substructure, luminosity functions and luminosity-weighted dynamics. Our calculations confirm that the group sizes, virial masses and luminosities cover the range expected for galaxy groups, except that the luminosity of NGC 4038 is boosted by the central starburst merger pair. We find that a combination of kinematical, substructural and dynamical techniques can reliably distinguish loose, unvirialized groups from compact, dynamically relaxed groups. Applying these techniques, we find that Dorado, NGC 4038 and NGC 4697 are unvirialized, whereas NGC 681, NGC 1400 and NGC 5084 are dynamically relaxed. [ABSTRACT FROM AUTHOR]

A generic prediction of hierarchical clustering models is that the mass function of dark haloes in dense regions in the Universe should be top-heavy. We provide a novel test of this prediction using a sample of galaxies drawn from the Sloan Digital Sky Survey (SDSS). To perform the test, we compare measurements of galaxy clustering in dense and underdense regions. We find that galaxies in dense regions cluster significantly more strongly than those in less dense regions. This is true over the entire 0.1–30 Mpc pair separation range for which we can make accurate measurements. We make similar measurements in realistic mock catalogues in which the only environmental effects are those which arise from the predicted correlation between halo mass and environment. We also provide an analytic halo model based calculation of the effect. Both the mock catalogues and the analytic calculation provide rather good descriptions of the SDSS measurements. Thus, our results provide strong support for hierarchical models. They suggest that, unless care is taken to study galaxies at fixed mass, correlations between galaxy properties and the surrounding environment are almost entirely due to more fundamental correlations between galaxy properties and host halo mass, and between halo mass and environment. [ABSTRACT FROM AUTHOR]

The optical rest-frame sizes of 10 of the most massive galaxies found in the near-infrared MUNICS survey at are analysed. Sizes are estimated in both the J and K′ filters. These massive galaxies are at least a factor of smaller in the rest-frame V-band than local counterparts of the same stellar mass. Consequently, the stellar mass density of these objects is (at least) 60 times larger than that of massive ellipticals today. Although the stellar populations of these objects are passively fading, their structural properties are rapidly changing since that redshift. This observational fact disagrees with a scenario where the more massive and passive galaxies are fully assembled at (i.e. a monolithic scenario) and points towards a dry merger scenario as the responsible mechanism for the subsequent evolution of these galaxies. [ABSTRACT FROM AUTHOR]

Some of the most-massive globular clusters of our Milky Way, such as, for example, ω Centauri, show a mixture of stellar populations spanning a few Gyr in age and 1.5 dex in metallicities. In contrast, standard formation scenarios predict that globular and open clusters form in one single starburst event of duration ≲10 Myr and therefore should exhibit only one age and one metallicity in its stars. Here, we investigate the possibility that a massive stellar supercluster may trap older galactic field stars during its formation process that are later detectable in the cluster as an apparent population of stars with a very different age and metallicity. With a set of numerical N-body simulations, we are able to show that, if the mass of the stellar supercluster is high enough and the stellar velocity dispersion in the cluster is comparable to the dispersion of the surrounding disc stars in the host galaxy, then up to about 40 per cent of its initial mass can be additionally gained from trapped disc stars. We also suggest that a supercluster may capture in excess of its own mass under certain conditions. [ABSTRACT FROM AUTHOR]

During the late stages of galaxy mergers or galactic interactions, supergiant molecular cloud complexes are turned into large numbers of stellar superclusters. Supergiant molecular cloud complexes show fractal structure due to turbulence and/or self-gravitation; therefore, superclusters formed out of these complexes are expected to exhibit similar geometry. Here we study the evolution of the multifractal pattern of the projected spatial distribution of supergiant molecular cloud complexes in the Antennae (NGC 4038/4039) as they turn into superclusters during the sustained starburst event. Using two data sets of the positions of supergiant molecular clouds and of stellar superclusters, the fractal spectrum is determined using the Minkowski-sausage method to calculate the Minkowski–Bouligand dimension as a function of the parameter q. For clouds, this measure varies with q in the range 0.7–2.2 for q in the interval [−4, 4]. For the projected distribution of superstar clusters it varies with q in the range 1.15–1.71. For the overlap region in the Antennae, the average projected fractal dimension of supergiant clouds is found to be 1.3 and the average fractal dimension of superclusters is 1.6. Our results indicate that during star formation the local fractal dimension increases, likely due to diffusion-like evolution. [ABSTRACT FROM AUTHOR]

We present an analysis of the effects of environment on the photometric properties of galaxies in the core of the Shapley supercluster at , one of the most massive structures in the local universe. The Shapley Optical Survey (SOS) comprises archive Wide Field Imager (WFI) optical imaging of a 2.0 deg2 region containing the rich clusters A3556, A3558 and A3562 which demonstrate a highly complex dynamical situation including ongoing cluster mergers. The B− R/ R colour–magnitude relation has an intrinsic dispersion of 0.045 mag and is 0.015 ± 0.005 mag redder in the highest-density regions, indicative of the red sequence galaxy population being 500-Myr older in the cluster cores than towards the virial radius. The B− R colours of galaxies are dependent on their environment, whereas their luminosities are independent of the local density, except for the very brightest galaxies . The global colours of faint galaxies change from the cluster cores where ∼90 per cent of galaxies lie along the cluster red sequence to the virial radius, where the fraction has dropped to just ∼20 per cent. This suggests that processes directly related to the supercluster environment are responsible for transforming faint galaxies, rather than galaxy merging, which should be infrequent in any of the regions studied here. The largest concentrations of faint blue galaxies are found between the clusters, coincident with regions containing high fractions of ∼ L* galaxies with radio emission indicating starbursts. Their location suggests star formation triggered by cluster mergers, in particular the merger of A3562 and the poor cluster SC 1329-313, although they may also represent recent arrivals in the supercluster core complex. The effect of the A3562–SC 1329-313 merger is also apparent as a displacement in the spatial distribution of the faint galaxy population from both the centres of X-ray emission and the brightest cluster galaxies for both systems. The cores of each of the clusters/groups are marked by regions that have the lowest blue galaxy fractions and reddest mean galaxy colours over the whole supercluster region, confirming that star formation rates are lowest in the cluster cores. In the cases of A3562 and SC 1329-313, these regions coincide with the centres of X-ray emission rather than the peaks in the local surface density, indicating that ram-pressure stripping may have an important role in terminating any remnant star formation in galaxies that encounter the dense intracluster medium (ICM) of the cluster cores. [ABSTRACT FROM AUTHOR]

We present GyVe, an interactive visualization tool for understanding structure in sparse three-dimensional (3D) point data. The scientific goal driving the tool's development is to determine the presence of filaments and voids as defined by inferred 3D galaxy positions within the Horologium-Reticulum supercluster (HAS). GyVe provides visualization techniques tailored to examine structures defined by the intercluster galaxies. Specific techniques include: interactive user control to move between a global overview and local viewpoints, labelled axes and curved drop lines to indicate positions in the astronomical RA-DEC-cz coordinate system, torsional rocking and stereo to enhance 3D perception, and geometrically distinct glyphs to show potential correlation between intercluster galaxies and known clusters. We discuss the rationale for each design decision and review the success of the techniques in accomplishing the scientific goals. In practice, GyVe has been useful for gaining intuition about structures that were difficult to perceive with 2D projection techniques alone. For example, during their initial session with GyVe, our collaborators quickly confirmed scientific conclusions regarding the large-scale structure of the HRS previously obtained over months of study with 2D projections and statistical techniques. Further use of GyVe revealed the spherical shape of voids and showed that a presumed filament was actually two disconnected structures. [ABSTRACT FROM AUTHOR]

Alignments of galaxy clusters (the Binggeli effect), as well as of galaxies themselves have long been studied both observationally and theoretically. Here, we test the influence of large-scale structures and tidal fields on the shapes and alignments of cluster-size and galaxy-size dark matter haloes. We use a high-resolution N-body simulation of a Λ cold dark matter (ΛCDM) universe, together with the results of Colberg, Krughoff & Connolly, who identified filaments connecting pairs of clusters. We find that cluster pairs connected by a filament are strongly aligned with the cluster–cluster axis, whereas unconnected ones are not. For smaller, galaxy-size haloes, there also is an alignment signal, but its strength is independent of whether the halo is part of an obvious large-scale structure. Additionally, we find no measurable dependence of galaxy halo shape on membership of a filament. We also quantify the influence of tidal fields and find that these do correlate strongly with alignments of haloes. The alignments of most haloes are thus caused by tidal fields, with cluster-size haloes being strongly aligned through the added mechanism of infall of matter from filaments. [ABSTRACT FROM AUTHOR]

We present the Shapley Optical Survey, a photometric study covering a ∼2-deg2 region of the Shapley supercluster core at in two bands ( B and R). The galaxy sample is complete to and . The galaxy luminosity function (LF) cannot be described by a single Schechter function due to dips apparent at and and the clear upturn in the counts for galaxies fainter than B and . We find, instead, that the sum of a Gaussian and a Schechter function, for bright and faint galaxies, respectively, is a suitable representation of the data. We study the effects of the environment on the photometric properties of galaxies, deriving the galaxy LFs in three regions selected according to the local galaxy density, and find a marked luminosity segregation, in the sense that the LF faint end is different at more than 3σ confidence level in regions with different densities. In addition, the LFs of red and blue galaxy populations show very different behaviours: while red sequence counts are very similar to those obtained for the global galaxy population, the blue galaxy LFs are well described by a single Schechter function and do not vary with the density. Such large environmentally dependent deviations from a single Schechter function are difficult to produce solely within galaxy merging or suffocation scenarios. Instead the data support the idea that mechanisms related to the cluster environment, such as galaxy harassment or ram-pressure stripping, shape the galaxy LFs by terminating star formation and producing mass-loss in galaxies at , a magnitude range where blue late-type spirals used to dominate cluster populations, but are now absent. [ABSTRACT FROM AUTHOR]

Abstract: In the near future a large number of galaxy clusters will be observed in surveys based on the Sunyaev-Zel''dovich effect (SZE) . Both the spherical and ellipsoidal models of the dark matter of galaxy clusters are adopted to make theoretical predictions of the number of observable S-Z galaxy clusters, and to asses the effect of the cluster shape on the calculation. By means of the virial equilibrium condition the mass lower limit of the observable galaxy clusters is determined from given survey flux lower limit and the prediction of the number count of galaxy clusters is carried out by the mass function. The calculated results show that if the cosmological parameters are to be constrained by the S-Z surveys, then the uncertainty in the shape of the clusters should be taken into account. [Copyright &y& Elsevier]

The progress of the studies on the orientation of galaxies in the Local Supercluster (LSC) is reviewed and a summary of recent results is given. Following a brief introduction of the LSC, we describe the results of early studies based on two-dimensional analysis, which were mostly not conclusive. We describe next the three-dimensional analysis, which is used widely today. Difficulties and systematic effects are explained and the importance of selection effects is described. Then, results based on the new method and modern databases are given, which are summarized as follows. When the LSC is seen as a whole, galaxy planes tend to align perpendicular to the LSC plane with lenticulars showing the most pronounced tendency. Projections onto the LSC plane of the spin vectors of Virgo cluster member galaxies, and to some extent, those of the total LSC galaxies, tend to point to the Virgo cluster center. This tendency is more pronounced for lenticulars than for spirals. It is suggested that ‘field’ galaxies, i.e., those which do not belong to groups with more than three members, may be better objects than other galaxies to probe the information at the early epoch of the LSC formation through the analysis of galaxy orientations. Field lenticulars show a pronounced anisotropic distribution of spin vectors in the sense that they lay their spin vectors parallel to the LSC plane while field spirals show an isotropic spin-vector distribution. [ABSTRACT FROM AUTHOR]

In this paper, we study the supercluster–cluster morphological properties using one of the largest smoothed particle hydrodynamics (SPH)+ N-body simulations of large-scale structure formation in a Λ cold dark matter (ΛCDM) model, based on the publicly available codegadget. We find that filamentary (prolate-like) shapes are the dominant supercluster and cluster dark matter halo morphological feature, in agreement with previous studies. However, the baryonic gas component of the clusters is predominantly spherical. We investigate the alignment between cluster haloes (using either their dark matter or their baryonic components) and their parent supercluster major-axis orientation, finding that clusters show such a preferential alignment. Combining the shape and the alignment statistics, we also find that the amplitude of supercluster–cluster alignment increases, although weakly, with supercluster filamentariness. [ABSTRACT FROM AUTHOR]

The Pisces-Cetus supercluster (redshift ) is one of the richest nearby superclusters of galaxies, and emerges as a remarkable filament of galaxies at the edges of the two-degree Field Galaxy Redshift Survey (2dFGRS) and the ongoing Sloan Digital Sky Survey (SDSS). We explore the extent of the supercluster on the sky and in redshift space, and map the distribution of its constituent clusters and groups. We find evidence of enhanced star formation in galaxies belonging to groups in the supercluster compared to those in the field. This effect appears to be higher among the poorer groups than in the richer ones. In contrast, star formation is suppressed in the galaxies in rich clusters, which is consistent with previous studies. We identify two major filaments in this supercluster, consisting of 11 and 5 Abell clusters, including Abell 133 and Abell 85, respectively, and estimate the virial masses of the clusters from their velocity dispersions and optical surface brightness profiles. The lower limit to the masses of these filaments, amounting to the total virial mass of the constituent clusters, turns out to be and over volumes of almost and , respectively. This corresponds to mass overdensities of and for the two filaments making up the supercluster. [ABSTRACT FROM AUTHOR]

We use a novel technique to simulate the growth of one of the most massive progenitors of a supercluster region from redshift z∼ 80, when its mass was about , until the present day. Our nested sequence of N-body resimulations allows us to study in detail the structure both of the dark matter object itself and of its environment. Our effective resolution is optimal at redshifts of 49, 29, 12, 5 and 0 when the dominant object has mass and , respectively, and contains simulation particles within its virial radius. Extended Press–Schechter (EPS) theory correctly predicts both this rapid growth and the substantial overabundance of massive haloes we find at early times in regions surrounding the dominant object. Although the large-scale structure in these regions differs dramatically from a scaled version of its present-day counterpart, the internal structure of the dominant object is remarkably similar. Molecular hydrogen cooling could start as early as z∼ 49 in this object, while cooling by atomic hydrogen becomes effective at z∼ 39. If the first stars formed in haloes with virial temperature ∼2000 K, their comoving abundance at z= 49 should be similar to that of dwarf galaxies today, while their comoving correlation length should be . [ABSTRACT FROM AUTHOR]

We present interferometric imaging at 33 GHz of the Corona Borealis supercluster, using the extended configuration of the Very Small Array. A total area of 24 deg2 has been imaged, with an angular resolution of 11 arcmin and a sensitivity of 12 mJy beam−1. The aim of these observations is to search for Sunyaev–Zel'dovich (SZ) detections from known clusters of galaxies in this supercluster and for a possible extended SZ decrement due to diffuse warm/hot gas in the intercluster medium. Hydrodynamical simulations suggest that a significant part of the missing baryons in the Local Universe may be located in superclusters. The maps constructed from these observations have a significant contribution from primordial fluctuations. We measure negative flux values in the positions of the 10 richest clusters in the region. Collectively, this implies a 3.0σ detection of the SZ effect. For two of these clusters, A2061 and A2065, we find decrements of approximately 2σ each. Our main result is the detection of two strong and resolved negative features at and , respectively, located in a region with no known clusters, near the centre of the supercluster. We discuss their possible origins in terms of primordial cosmic microwave background (CMB) anisotropies and/or SZ signals related either to unknown clusters or to a diffuse extended warm/hot gas distribution. Our analyses have revealed that a primordial CMB fluctuation is a plausible explanation for the weaker feature (probability of 37.82 per cent). For the stronger one, neither primordial CMB (probability of 0.38 per cent) nor SZ can account alone for its size and total intensity. The most reasonable explanation, then, is a combination of both primordial CMB and SZ signal. Finally, we explore what characteristics would be required for a filamentary structure consisting of warm/hot diffuse gas in order to produce a significant contribution to such a spot taking into account the constraints set by X-ray data. [ABSTRACT FROM AUTHOR]

We use high-resolution hydrodynamical simulations of large-scale structure formation to study the imprints of the local superclusters on to the full-sky Sunyaev–Zel'dovich (SZ) signals. Following Mathis et al., the initial conditions have been statistically constrained to reproduce the density field within a sphere of 110 Mpc around the Milky Way, as observed in the IRAS 1.2-Jy all-sky redshift survey. As a result, the positions and masses of prominent galaxy clusters and superclusters in our simulations coincide closely with their real counterparts in the local Universe. We present the results of two different runs: one with adiabatic gas physics only, and one also including cooling, star formation and feedback. By analysing the full-sky maps for the thermal and kinetic SZ signals extracted from these simulations, we find that for multipoles with the power spectrum is dominated by the prominent local superclusters, and its amplitude at these scales is a factor of 2 higher than that obtained from unconstrained simulations; at lower multipoles ( ) this factor can even reach one order of magnitude. We check the influence of the SZ effect from local superclusters on the cosmic microwave background (CMB) power spectrum at small multipoles and find it negligible and with no signs of quadrupole–octopole alignment. However, performing simulations of the CMB radiation including the experimental noise at the frequencies which will be observed by the Planck satellite, we find results suggesting that an estimate of the SZ power spectrum at large scales can be extracted. [ABSTRACT FROM AUTHOR]

We compute the real-space cluster–galaxy cross-correlation ξcg( r) using the ROSAT-ESO Flux Limited X-ray (REFLEX) cluster survey, a group catalogue (2dFGGC) constructed from the final version of the Two-degree Field Galaxy Redshift Survey (2dFGRS), and galaxies extracted from the Two Micron All Sky Survey (2MASS) and Automated Plate Measurement (APM) surveys. This first detailed calculation of the cross-correlation for X-ray clusters and groups is consistent with previous works and shows that ξcg( r) cannot be described by a single power law. We analyse the clustering dependence on the cluster X-ray luminosity LX and virial mass Mvir thresholds as well as on the galaxy limiting magnitude. We also make a comparison of our results with those obtained for the halo–mass cross-correlation function in a ΛCDM N-body simulation to infer the scale dependence of galaxy bias around clusters. Our results indicate that the distribution of galaxies shows a significant anti-bias at highly non-linear small cluster-centric distances, , irrespective of the group/cluster virial mass or X-ray luminosity and galaxy characteristics. This shows that a generic process controls the efficiency of galaxy formation and evolution in high-density regions. On larger scales, bcg( r) rises to a nearly constant value of the order of unity, the transition occurring at approximately 2 h−1 Mpc for 2dF groups and 5 h−1 Mpc for REFLEX clusters. [ABSTRACT FROM AUTHOR]

We make an exploratory study of how well dark energy models can be constrained using lensed arcs at different redshifts behind cluster lenses. Arcs trace the critical curves of clusters, and the growth of critical curves with source redshift is sensitive to the dark energy equation of state. Using analytical models and numerically simulated clusters, we explore the key factors involved in using cluster arcs as a probe of dark energy. We quantify the sensitivity to lens mass, concentration and ellipticity with analytical models that include the effects of dark energy on halo structure. We show with simple examples how degeneracies between mass models and cosmography may be broken using arcs at multiple redshifts or additional constraints on the lens density profile. However, we conclude that the requirements on the data are so stringent that it is very unlikely that robust constraints can be obtained from individual clusters. We argue that surveys of clusters, analysed in conjunction with numerical simulations, are a more promising prospect for arc cosmography. We use such numerically simulated clusters to estimate how large a sample of clusters/arcs could provide interesting constraints on dark energy models. We focus on the scatter produced by differences in the mass distribution of individual clusters. We find from our sample of simulated clusters that at least 1000 pairs of arcs are needed to obtain constraints if the mass distribution of individual clusters is taken to be undetermined. We discuss several unsolved problems that need study to develop this method fully for precision studies with future surveys. [ABSTRACT FROM AUTHOR]

A method for estimating redshifts of galaxy clusters based solely on resolved Sunyaev–Zel'dovich (SZ) images is proposed. Given a high-resolution SZ cluster image (with a FWHM of ∼1 arcmin), the method indirectly measures its structure-related parameters (amplitude, size, etc.) by fitting a model function to the higher-order wavelet moments of the cluster's SZ morphology. The applicability and accuracy of the wavelet method are assessed by applying the method to maps of a set of clusters extracted from hydrodynamical simulations of cosmic structure formation. The parameters, derived by a fit to the spectrum of wavelet moments as a function of scale, are found to show a dependence on redshift z that is of the type , where the monotony of this functional behaviour and the non-degeneracy of those parameters allow inversion and estimation of the redshift z. The average attainable accuracy in the z estimation relative to 1 + z is ∼4–5 per cent out to , which is comparable with photometric redshifts. For single-frequency SZ interferometers, in which the ambient fluctuating CMB is the main noise source, the accuracy of the method drops slightly to per cent. Other complications addressed include instrumental noise, cold cores and systematic trends in baryon fraction with cluster mass. [ABSTRACT FROM AUTHOR]

Voids are a prominent feature of fractal point distributions but there is no precise definition of what is a void (except in one dimension). Here we propose a definition of voids that uses methods of discrete stochastic geometry, in particular, Delaunay and Voronoi tessellations, and we construct a new algorithm to search for voids in a point set. We find and rank-order the voids of suitable examples of fractal point sets in one and two dimensions to test whether Zipf’s power-law holds. We conclude affirmatively and, furthermore, that the rank-ordering of voids conveys similar information to the number-radius function, as regards the scaling regime and the transition to homogeneity. So it is an alternative tool in the analysis of fractal point distributions with crossover to homogeneity and, in particular, of the distribution of galaxies. [ABSTRACT FROM AUTHOR]

A multiscale model of the MJO is developed here that accounts, in a simplified fashion, for both the upscale transfer from synoptic to planetary scales of momentum and temperature from wave trains of thermally driven equatorial synoptic-scale circulations in a moving convective envelope as well as direct mean heating on planetary scales. This model involves idealized thermally driven congestus synoptic-scale fluctuations in the eastern part of the moving wave envelope and convective superclusters in the western part of the envelope. The model self-consistently reproduces qualitatively many of the detailed structural features of the planetary circulation in the observations of the MJO, including the vertical structure in both the westerly onset region and the strong westerly wind burst region, as well as the horizontal quadrupole planetary vortex structure. The westerly midlevel inflow in the strong westerly region and the quadrupole vortex are largely produced in the model by the upscale transport of momentum to the planetary scales, while the midlevel easterly jet in the westerly onset region is substantially strengthened by this process. The role of wave trains of tilted organized synoptic-scale circulations is crucial for this fidelity with observations. The appeal of the multiscale models developed below is their firm mathematical underpinnings, simplicity, and analytic tractability while remaining self-consistent with many of the features of the observational record. [ABSTRACT FROM AUTHOR]