28 research outputs found

    Cluster Lenses

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    Clusters of galaxies are the most recently assembled, massive, bound structures in the Universe. As predicted by General Relativity, given their masses, clusters strongly deform space-time in their vicinity. Clusters act as some of the most powerful gravitational lenses in the Universe. Light rays traversing through clusters from distant sources are hence deflected, and the resulting images of these distant objects therefore appear distorted and magnified. Lensing by clusters occurs in two regimes, each with unique observational signatures. The strong lensing regime is characterized by effects readily seen by eye, namely, the production of giant arcs, multiple-images, and arclets. The weak lensing regime is characterized by small deformations in the shapes of background galaxies only detectable statistically. Cluster lenses have been exploited successfully to address several important current questions in cosmology: (i) the study of the lens(es) - understanding cluster mass distributions and issues pertaining to cluster formation and evolution, as well as constraining the nature of dark matter; (ii) the study of the lensed objects - probing the properties of the background lensed galaxy population - which is statistically at higher redshifts and of lower intrinsic luminosity thus enabling the probing of galaxy formation at the earliest times right up to the Dark Ages; and (iii) the study of the geometry of the Universe - as the strength of lensing depends on the ratios of angular diameter distances between the lens, source and observer, lens deflections are sensitive to the value of cosmological parameters and offer a powerful geometric tool to probe Dark Energy. In this review, we present the basics of cluster lensing and provide a current status report of the field.Comment: About 120 pages - Published in Open Access at: http://www.springerlink.com/content/j183018170485723/ . arXiv admin note: text overlap with arXiv:astro-ph/0504478 and arXiv:1003.3674 by other author

    A review of elliptical and disc galaxy structure, and modern scaling laws

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    A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their models to describe the radial distribution of stars in `nebulae'. This article reviews the progress since then, providing both an historical perspective and a contemporary review of the stellar structure of bulges, discs and elliptical galaxies. The quantification of galaxy nuclei, such as central mass deficits and excess nuclear light, plus the structure of dark matter halos and cD galaxy envelopes, are discussed. Issues pertaining to spiral galaxies including dust, bulge-to-disc ratios, bulgeless galaxies, bars and the identification of pseudobulges are also reviewed. An array of modern scaling relations involving sizes, luminosities, surface brightnesses and stellar concentrations are presented, many of which are shown to be curved. These 'redshift zero' relations not only quantify the behavior and nature of galaxies in the Universe today, but are the modern benchmark for evolutionary studies of galaxies, whether based on observations, N-body-simulations or semi-analytical modelling. For example, it is shown that some of the recently discovered compact elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to appear in "Planets, Stars and Stellar Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references incl. many somewhat forgotten, pioneer papers. Original submission to Springer: 07-June-201

    The course of radiologic damage during the first six years of rheumatoid arthritis

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    Objective. To describe the radiologic course in a large cohort of patients with early rheumatoid arthritis (RA) and to analyze individual components of damage. Methods. Five hundred two patients with recent-onset RA (disease duration Results. Stable rates of progression of the SHS, erosion score, and narrowing score were found over the course of RA: the mean rates were 8.6, 5.4, and 3.2 modified Sharp units per year, respectively. The rate of progression of newly (not previously) damaged joints declined, and the rate of progression of already damaged joints (which became more damaged) increased during followup, leading to an equal contribution to progression of the SHS at 5 years. The joints of the feet, especially the fifth metatarsophalangeal joint, generally became eroded earlier and more of them became eroded compared with the joints of the hands. Conclusion. Radiologic damage progresses at a constant rate. In advanced disease, monitoring the progression of previously existing damage is as important as assessing new abnormalities in previously undamaged joints. Radiographs of the feet should be included in assessments of radiologic damage that are used in clinical intervention trials and daily practice

    The course of radiologic damage during the first six years of rheumatoid arthritis

    No full text
    To describe the radiologic course in a large cohort of patients with early rheumatoid arthritis (RA) and to analyze individual components of damage. Five hundred two patients with recent-onset RA (disease duration <1 year) underwent annual radiologic assessment for a maximum of 6 years in this longitudinal prospective study. The study was designed to investigate the efficacy of 3 different therapeutic strategies. For the assessment of radiologic damage, radiographs of the hands and feet were scored according to the modified Sharp/van der Heijde method (SHS; range 0-448). A mean of 2.9 (range 1-7) radiographs was read per patient. Stable rates of progression of the SHS, erosion score, and narrowing score were found over the course of RA: the mean rates were 8.6, 5.4, and 3.2 modified Sharp units per year, respectively. The rate of progression of newly (not previously) damaged joints declined, and the rate of progression of already damaged joints (which became more damaged) increased during followup, leading to an equal contribution to progression of the SHS at 5 years. The joints of the feet, especially the fifth metatarsophalangeal joint, generally became eroded earlier and more of them became eroded compared with the joints of the hands. Radiologic damage progresses at a constant rate. In advanced disease, monitoring the progression of previously existing damage is as important as assessing new abnormalities in previously undamaged joints. Radiographs of the feet should be included in assessments of radiologic damage that are used in clinical intervention trials and daily practic
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