60,414 research outputs found

    A Hubble Space Telescope Survey of X-ray Luminous Galaxy Clusters: Gravitationally Lensed Arcs and EROs

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    We are conducting a systematic lensing survey of X-ray luminous galaxy clusters at z~0.2 using the Hubble Space Telescope and large ground-based telescopes. We summarize initial results from our survey, including a measurement of the inner slope of the mass profile of A383, and a search for gravitationally lensed Extremely Red Objects.Comment: 4 pages, 2 figures. To appear in "A New Era in Cosmology" (ASP Conference Proceedings), eds. T. Shanks and N. Metcalf

    Taxonomy of some Galeommatoidea (Mollusca, Bivalvia) associated with deep-sea echinoids: A reassessment of the bivalve genera Axinodon Verrill & Bush, 1898 and Kelliola Dall, 1899 with descriptions of new genera Syssitomya gen. nov. and Ptilomyax gen. nov.

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    The type species of Axinodon ellipticus Verrill & Bush, 1898 and Kellia symmetros Jeffreys, 1876 are re-described. It is concluded that the two species are not conspecific and that K. symmetros cannot be placed in the genus Axinodon. The family affinity of Axinodon is not resolved, although it is probable that this genus belongs to the Thyasiridae. Kellia symmetros is the type species of Kelliola and is placed in the Montacutidae. Kelliola symmetros is most probably associated with the echinoid Aeropsis rostrata and is not the species previously recorded from North Atlantic Pourtalesia echinoids under the name of Axinodon symmetros. This commensal associated with the North Atlantic Pourtalesia is here described as new and placed in the new genus as Syssitomya pourtalesiana gen. nov. sp. nov., Syssitomya gen. nov. differs from all other genera in the Montacutidae by having laminar gill filaments modified for harbouring symbiotic bacteria and it is thus assumed to be chemosymbiotic. A montacutid associated with the hadal Pourtalesia heptneri is described as Ptilomyax hadalis gen. nov. sp. nov

    Hubble, chandra and keck constraints on massive galaxy clusters at z=0.2 and z=0.5

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    I present recent observations from two Hubble Space Telescope(HST)/ACS programs that target the most X–ray luminous and thus (presumably) most massive galaxy clusters at z=0.5 – the highest redshift at which complete, well–defined samples of such rare systems are available. The first program (GO:9836, PI: R.S. Ellis) exploits a huge mosaic of 41 ACS pointings spanning a 10 Mpc region centered on MS0451-03. This is the largest contiguous space–based image of a cluster to date. I describe a preliminary weak–lensing analysis and a new Keck/DEIMOS redshift catalog of 1000 galaxies in this field. The second program (GO:9722, PI: H. Ebeling) studies the core regions of the twelve most luminous clusters at z≥0.5 from the MAssive Cluster Survey (MACS; Ebeling et al. 2001). Multi–color ACS observations in combination with recent Keck/LRIS spectroscopy of gravitational arcs constrain the distribution of mass in the cluster cores, thus laying the foundation for detailed multi–diagnostic (lensing, X–ray, near–infrared, SZE) investigation of this sample. For example, it is of particular interest to explore how the structure and state of relaxation of massive clusters evolved between this sample at z≥0.5 that measured by Smith et al. (2004, astro–ph/0403588) at z=0.2

    LoCuSS: Weak-lensing mass calibration of galaxy clusters

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    We present weak-lensing mass measurements of 50 X-ray luminous galaxy clusters at 0.15z0.30.15\le z\le0.3, based on uniform high quality observations with Suprime-Cam mounted on the 8.2-m Subaru telescope. We pay close attention to possible systematic biases, aiming to control them at the 4\le4 per cent level. The dominant source of systematic bias in weak-lensing measurements of the mass of individual galaxy clusters is contamination of background galaxy catalogues by faint cluster and foreground galaxies. We extend our conservative method for selecting background galaxies with (Vi)(V-i') colours redder than the red sequence of cluster members to use a colour-cut that depends on cluster-centric radius. This allows us to define background galaxy samples that suffer 1\le1 per cent contamination, and comprise 1313 galaxies per square arcminute. Thanks to the purity of our background galaxy catalogue, the largest systematic that we identify in our analysis is a shape measurement bias of 33 per cent, that we measure using simulations that probe weak shears upto g=0.3g=0.3. Our individual cluster mass and concentration measurements are in excellent agreement with predictions of the mass-concentration relation. Equally, our stacked shear profile is in excellent agreement with the Navarro Frenk and White profile. Our new LoCuSS mass measurements are consistent with the CCCP and CLASH surveys, and in tension with the Weighing the Giants at 12σ\sim1-2\sigma significance. Overall, the consensus at z0.3z\le0.3 that is emerging from these complementary surveys represents important progress for cluster mass calibration, and augurs well for cluster cosmology.Comment: 30 pages, 14 figures, 7 tables : accepted for the publication in MNRAS : mass table update

    Bi-directional route learning in wood ants

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    Some ants and bees readily learn visually guided routes between their nests and feeding sites. They can learn the appearance of visual landmarks for the food-bound or homeward segment of the route when these landmarks are only present during that particular segment of their round trip. We show here that wood ants can also acquire landmark information for guiding their homeward path while running their food-bound path, and that this information may be picked up, when ants briefly reverse direction and retrace their steps for a short distance. These short periods of looking back tend to occur early in route acquisition and are more frequent on homeward than on food-bound segments

    Carbon in soils

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    Carbon is the fourth most common element in the galaxy(by mass) but does not even rank in the twelve most abundant elements on Earth. By far the most abundant source of carbon on Earth is in the crust as inorganic rocks such as calcite and limestone in marine and sedimentary deposits. These rocks have taken many millions of years to form. Other major inorganic sources are in the oceans and atmosphere

    Holonomy and Projective Equivalence in 4-Dimensional Lorentz Manifolds

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    A study is made of 4-dimensional Lorentz manifolds which are projectively related, that is, whose Levi-Civita connections give rise to the same (unparameterised) geodesics. A brief review of some relevant recent work is provided and a list of new results connecting projective relatedness and the holonomy type of the Lorentz manifold in question is given. This necessitates a review of the possible holonomy groups for such manifolds which, in turn, requires a certain convenient classification of the associated curvature tensors. These reviews are provided.Comment: Comments: 23 pages, LaTeX; typos corrected, page 9 last line corrected to $g'=e^{2\chi}a^{-1}
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