1,721,082 research outputs found
The PLANET collaboration - Probing lensing anomalies with a world-wide NETwork
No full textA newly-formed microlensing monitoring network, the PLANET collaboration, is briefly described
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Microlensing & scintillation of gravitationally lensed compact radio sources:Evidence for MACHOs?
No full textWe present the first unambiguous case of external variability of an extra-galactic radio source, the CLASS gravitational lens B1600+434, consisting of two images lensed by an edge-on disk galaxy. The VLA 8.5-GHz difference light curve of the lens images shows external variability at the 14.6-sigma confidence level. Although the current single-frequency VLA observations cannot conclusively exclude scintillation, several lines of evidence show that it does not dominate the short-term variability. This is supported by an ongoing three-frequency WSRT campaign. If scintillation is the dominant source of this external variability, it would require very different properties of the Galactic ionized ISM towards the two lens images. Microlensing of a superluminal jet component can explain both the rms and time-scale of variability, but requires the halo of the lens galaxy to be filled with greater than or similar to0.5-M-circle dot MACHOs. The current data appear to support microlensing as the dominant source of the observed external variability.</p
Microlensing & scintillation of gravitationally lensed compact radio sources:Evidence for MACHOs?
No full textWe present the first unambiguous case of external variability of an extra-galactic radio source, the CLASS gravitational lens B1600+434, consisting of two images lensed by an edge-on disk galaxy. The VLA 8.5-GHz difference light curve of the lens images shows external variability at the 14.6-sigma confidence level. Although the current single-frequency VLA observations cannot conclusively exclude scintillation, several lines of evidence show that it does not dominate the short-term variability. This is supported by an ongoing three-frequency WSRT campaign. If scintillation is the dominant source of this external variability, it would require very different properties of the Galactic ionized ISM towards the two lens images. Microlensing of a superluminal jet component can explain both the rms and time-scale of variability, but requires the halo of the lens galaxy to be filled with greater than or similar to0.5-M-circle dot MACHOs. The current data appear to support microlensing as the dominant source of the observed external variability.</p
Mass and mass-to-light ratio of galaxy groups from weak lensing
No full textWe have measured for the first time the weak lensing signal due to groups of galaxies. The groups are at intermediate redshifts, and have been identified in the CNOC2 field survey, which was kindly made available by Ray Carlberg and Howard Yee. The ensemble averaged group velocity dispersion, based on a preliminary selection of 59 groups, is found to be (1/2) = 320(-54)(+46) km/s, which is in fair agreement with the dynamical estimate from the spectroscopic redshifts. Under the assumption that mass traces light, we find an average mass-to-light ratio in restframe B of (256+/-84)hM(circle dot)/LBcircle dot(E). Using this result we obtain Omega(m) = 0.22+/-0.09 (Omega(A) = 0).</p
Gravitational Lenses and Damped Ly-alpha Systems
Get PDFWe study the influence of gravitational lensing on determinationing the number density and column density distributions of damped Ly-alpha systems.</p
A common high-column density LY-alpha line in the spectra of Q 1429-008 A&B
No full textWe observed a common high-column density Ly-alpha absorption Line in the spectra of both Q 1429-008 A & B, but with different equivalent widths.</p
The distribution of dark mass in galaxies
No full textGravitational lensing is one of a number of methods used to probe the distribution of dark mass in the Universe. On galactic scales, complementary techniques include the use of stellar kinematics, the kinematics and morphology of the neutral gas layer, kinematics of satellites, and the morphology and temperature profile of X-ray halos. These methods are compared, with emphasis on their relative strengths and weaknesses in constraining the distribution and extent of dark matter in the Milky Way and other galaxies. It is concluded that (1) the extent of dark halos remains ill-constrained, (2) halos need not be isothermal, and (3) the dark mass is probably quite flattened.</p
Mass and mass-to-light ratio of galaxy groups from weak lensing
No full textWe have measured for the first time the weak lensing signal due to groups of galaxies. The groups are at intermediate redshifts, and have been identified in the CNOC2 field survey, which was kindly made available by Ray Carlberg and Howard Yee. The ensemble averaged group velocity dispersion, based on a preliminary selection of 59 groups, is found to be (1/2) = 320(-54)(+46) km/s, which is in fair agreement with the dynamical estimate from the spectroscopic redshifts. Under the assumption that mass traces light, we find an average mass-to-light ratio in restframe B of (256+/-84)hM(circle dot)/LBcircle dot(E). Using this result we obtain Omega(m) = 0.22+/-0.09 (Omega(A) = 0).</p
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