We present a study of the shape, size, and spatial orientation of superclusters of galaxies. Approximating superclusters by triaxial ellipsoids we show that superclusters are flattened, triaxial objects. We find that there are no spherical superclusters. The sizes of superclusters grow with their richness: the median semi-major axis of rich and poor superclusters (having >=8 and <8 member clusters) is 42 and 31h^-1^Mpc, respectively. Similarly, the median semi-minor axis is 12 and 5h^-1^Mpc for rich and poor superclusters. The spatial orientation of superclusters, as determined from the axes of the ellipsoids, is nearly random. We do not detect any preferable orientation of superclusters, neither with respect to the line of sight, nor relative to some other outstanding feature in the large scale structure, nor with respect to the directions of principal axes of adjacent superclusters.
Observations of early-type galaxies, both in the local Universe and in clusters at medium redshifts, suggest that these galaxies often contain discs or disc-like structures. Using the results of Kelson et al. (2000ApJ...531..137K) for the incidence of disc-components among the galaxies in the redshift z=0.33 cluster CL 1358+62, we investigate the effect of disc structures on the lensing properties of early-type galaxies. Statistical properties, like magnification cross-sections and the expected number of quad (four-image) lens systems, are not affected greatly by the inclusion of discs that contain less than ~10 per cent of the total stellar mass.
We compare the apparent axial ratio distributions of the brightest cluster galaxies (BCGs) and normal ellipticals (Es) in our sample of 75 galaxy clusters from the WIde-field Nearby Galaxy-cluster Survey (WINGS). Most BCGs in our clusters (69 per cent) are classified as cD galaxies. The sample of cDs has been completed by 14 additional cDs (non-BCGs) we found in our clusters. We deproject the apparent axial ratio distributions of Es, BCGs and cDs using a bivariate version of the Lucy rectification algorithm, whose results are supported by an independent Monte Carlo technique. Finally, we compare the intrinsic shape distribution of BCGs to the corresponding shape distribution of the central part of cluster-sized dark matter haloes extracted from the GIF2 Lambda cold dark matter ({LAMBDA}CDM) N-body simulations (Gao et al., 2004MNRAS.355..819G).
We study the supercluster shape properties of the recently compiled Sloan Digital Sky Survey (SDSS) cluster catalogue using an approach based on differential geometry. We detect superclusters by applying the percolation algorithm to observed cluster populations, extended out to z_max_<=0.23 in order to avoid selection biases. We utilize a set of shapefinders in order to study the morphological features of superclusters with >=8 cluster members and find that filamentary morphology is the dominant supercluster shape feature, in agreement with previous studies.
We report velocity measurements of galaxies in this, the densest mass concentration within z=0.1, obtained with the multifiber spectrograph MEFOS at ESO, La Silla. We derive redshifts of a number of Abell clusters and draw implications for the supercluster structure. The clusters A3554, A3566, A3577 and AS718 are confirmed as members, while the clusters A3524, A3531, A3542, A3545 and A3549 are shown to be background systems and A3581 a foreground one
Backreactions from large-scale inhomogeneities may provide an elegant explanation for the observed accelerated expansion of the universe without the need to introduce dark energy. We propose a cosmological test for a specific model of inhomogeneous cosmology, called timescape cosmology. Using large-scale galaxy surveys such as SDSS and 2MRS, we test the variation of expansion expected in the {Lambda}-CDM model versus a more generic differential expansion using our own calibrations of bounds suggested by timescape cosmology. Our test measures the systematic variations of the Hubble flow towards distant galaxies groups as a function of the matter distribution in the lines of sight to those galaxy groups. We compare the observed systematic variation of the Hubble flow to mock catalogues from the Millennium Simulation in the case of the {Lambda}-CDM model, and a deformed version of the same simulation that exhibits more pronounced differential expansion. We perform a series of statistical tests, ranging from linear regressions to Kolmogorov-Smirnov tests, on the obtained data. They consistently yield results preferring {Lambda}-CDM cosmology over our approximated model of timescape cosmology. Our analysis of observational data shows no evidence that the variation of expansion differs from that of the standard {Lambda}-CDM model.
We present new R-band photometric data for 447 galaxies, gathered for the Streaming Motions of Abell Clusters (SMAC) project. The data comprise 629 individual measurements of the Fundamental Plane (FP) parameters effective radius (Re) and surface brightness (<{mu}>_e_), derived from R^1/4^-law profile fitting. More than a third of the galaxies were observed more than once.
We report the construction of a new, standardized all-sky catalogue of Fundamental Plane (FP) data from early-type galaxies in clusters, for peculiar velocity applications. This catalogue is based on a compilation of spectroscopic and photometric data consisting of data reported in previous papers of this series, plus data from published sources.
We present a homogeneous catalog of 275 large (effective radius >~5.3") ultra-diffuse galaxy (UDG) candidates lying within an ~290deg^2^ region surrounding the Coma Cluster. The catalog results from our automated postprocessing of data from the Legacy Surveys, a three-band imaging survey covering 14000deg^2^ of the extragalactic sky. We describe a pipeline that identifies UDGs and provides their basic parameters. The survey is as complete in these large UDGs as previously published UDG surveys of the central region of the Coma Cluster. We conclude that the majority of our detections are at roughly the distance of the Coma Cluster, implying effective radii >=2.5kpc, and that our sample contains a significant number of analogs of DF44 (SMDG1300580+265835), where the effective radius exceeds 4kpc, both within the cluster and in the surrounding field. The g-z color of our UDGs spans a large range, suggesting that even large UDGs may reflect a range of formation histories. A majority of the UDGs are consistent with being lower stellar mass analogs of red sequence galaxies, but we find both red and blue UDG candidates in the vicinity of the Coma Cluster and a relative overabundance of blue UDG candidates in the lower-density environments and the field. Our eventual processing of the full Legacy Surveys data will produce the largest, most homogeneous sample of large UDGs.
