4,267 research outputs found
First detection of galaxy-galaxy-galaxy lensing in RCS. A new tool for studying the matter environment of galaxy pairs
The weak gravitational lensing effect, small coherent distortions of galaxy
images by means of a gravitational tidal field, can be used to study the
relation between the matter and galaxy distribution. In this context, weak
lensing has so far only been used for considering a second-order correlation
function that relates the matter density and galaxy number density as a
function of separation. We implement two new, third-order correlation functions
that have recently been suggested in the literature, and apply them to the
Red-Sequence Cluster Survey. We demonstrate that it is possible, even with
already existing data, to make significant measurements of third-order lensing
correlations. We develop an optimised computer code for the correlation
functions. To test its reliability a set of tests are performed. The
correlation functions are transformed to aperture statistics, which allow easy
tests for remaining systematics in the data. In order to further verify the
robustness of our measurement, the signal is shown to vanish when randomising
the source ellipticities. Finally, the lensing signal is compared to crude
predictions based on the halo-model. On angular scales between roughly 1 arcmin
and 11 arcmin a significant third-order correlation between two lens positions
and one source ellipticity is found. We discuss this correlation function as a
novel tool to study the average matter environment of pairs of galaxies.
Correlating two source ellipticities and one lens position yields a less
significant but nevertheless detectable signal on a scale of 4 arcmin. Both
signals lie roughly within the range expected by theory which supports their
cosmological origin.[ABRIDGED]Comment: 15 pages, 12 figures, accepted by A&A; minor change
The water footprint assessment manual: setting the global standard
This book contains the global standard for \u27water footprint assessment\u27 as developed and maintained by the Water Footprint Network (WFN). It covers a comprehensive set of definitions and methods for water footprint accounting. It shows how water footprints are calculated for individual processes and products, as well as for consumers, nations and businesses. It also includes methods for water footprint sustainability assessment and a library of water footprint response options. A shared standard on definitions and calculation methods is crucial given the rapidly growing interest in companies and governments to use water footprint accounts as a basis for formulating sustainable water strategies and policies
Addressing Indiaâs water challenge 2050: the virtual water trade option
The Government of India, on directions from the Supreme Court in 2002 and advice from the National Water Development Agency (NWDA), proposed an estimated US$120 billion National River Linking Project (NRLP) which envisages linking 37 Himalayan and Peninsular rivers (Figure 1; NCIWRD 1999). Doing this will form a gigantic South Asian water grid which will annually handle 178Ă109 m3/yr of interbasin water transfer; build 12,500 km of canals; generate 34 gigawatts of hydropower; add 35 million hectares (Mha) to Indiaâs irrigated areas; and generate inland navigation benefits (IWMI 2003; NWDA 2006; Gupta and van der Zaag 2007)
PKS 1004+13: A High-Inclination, Highly-Absorbed Radio-Loud QSO -- The First Radio-Loud BAL QSO at Low Redshift?
The existence of BAL outflows in only radio-quiet QSOs was thought to be an
important clue to mass ejection and the radio-loud - radio-quiet dichotomy.
Recently a few radio-loud BAL QSOs have been discovered at high redshift. We
present evidence that PKS 1004+13 is a radio-loud BAL QSO. It would be the
first known at low-redshift (z = 0.24), and one of the most radio luminous. For
PKS 1004+13, there appear to be broad absorption troughs of O VI, N V, Si IV,
and C IV, indicating high-ionization outflows up to about 10,000 km/s. There
are also two strong, broad (~500 km/s), high-ionization, associated absorption
systems that show partial covering of the continuum source. The strong UV
absorption we have detected suggests that the extreme soft-X-ray weakness of
PKS 1004+13 is primarily the result of absorption. The large radio-lobe
dominance indicates BAL and associated gas at high inclinations to the central
engine axis, perhaps in a line-of-sight that passes through an accretion disk
wind.Comment: To appear in Ap.J. Letters, 1999 (June or July); 4 pages, 5 figure
Sediment-moss interactions on a temperate glacier: Falljökull, Iceland
Full text of this article can be found at: http://www.igsoc.org/annals/ Copyright IGS. DOI: 10.3189/172756408784700734We present the results of preliminary investigations of globular moss growth on the surface of Falljökull, a temperate outlet glacier of the Vatnajökull ice cap, southern Iceland. Supraglacial debris has provided a basis for moss colonization, and several large (>500 m2) patches of moss growth (Racomitrium spp.) are observed on the surface of the glacier. Each area of moss-colonized supraglacial debris shows a downslope increase in sphericity and moss cushion size and a decrease in percentage surface coverage of moss-colonized and bare clasts. It is suggested that moss growth on supraglacial debris allows preferential downslope movement of clasts through an associated increase in both overall mass and sphericity. Thermal insulation by moss cushions protects the underlying ice surface from melt, and the resulting ice pedestals assist in downslope sliding and toppling of moss cushions. The morphology and life cycle of supraglacial globular mosses is therefore not only closely linked to the presence and distribution of supraglacial debris, but also appears to assist in limited down-glacier transport of this debris. This research highlights both the dynamic nature of the interaction of mosses with supraglacial sedimentary systems and the need for a detailed consideration of their role within the wider glacial ecosystem.Peer reviewe
Hubble Space Telescope weak lensing study of the z=0.83 cluster MS 1054-03
We have measured the weak gravitational lensing signal of MS 1054-03, a rich
and X-ray luminous cluster of galaxies at a redshift of z=0.83, using a
two-colour mosaic of deep WFPC2 images. The small corrections for the size of
the PSF and the high number density of background galaxies obtained in these
observations result in an accurate and well calibrated measurement of the
lensing induced distortion. The strength of the lensing signal depends on the
redshift distribution of the background galaxies. We used photometric redshift
distributions from the Northern and Southern Hubble Deep Fields to relate the
lensing signal to the mass. The predicted variations of the signal as a
function of apparent source magnitude and colour agrees well with the observed
lensing signal. We determine a mass of (1.2+-0.2)x10^15 Msun within an aperture
of radius 1 Mpc. Under the assumption of an isothermal mass distribution, the
corresponding velocity dispersion is 1311^{+83}_{-89} km/s. For the
mass-to-light ratio we find 269+-37 Msun/Lsun. The errors in the mass and
mass-to-light ratio include the contribution from the random intrinsic
ellipticities of the source galaxies, but not the (systematic) error due to the
uncertainty in the redshift distribution. However, the estimates for the mass
and mass-to-light ratio of MS 1054-03 agree well with other estimators,
suggesting that the mass calibration works well. The reconstruction of the
projected mass surface density shows a complex mass distribution, consistent
with the light distribution. The results indicate that MS 1054-03 is a young
system. The timescale for relaxation is estimated to be at least 1 Gyr.
Averaging the tangential shear around the cluster galaxies, we find that the
velocity dispersion of an Lstar galaxy is 203+-33 km/s.Comment: 21 pages, Latex, with 27 figures (3 figures bitmapped), ApJ, in
press. Version (with non-bitmapped figures) available at
http://www.astro.rug.nl/~hoekstra/papers.htm
Constraints on Omega_m and sigma_8 from weak lensing in RCS fields
We have analysed 53 square degrees of imaging data from the Red-Sequence
Cluster Survey (RCS), and measured the excess correlations in the shapes of
galaxies on scales out to ~1.5 degrees. We separate the signal into an ``E''-
(lensing) and ``B''-mode (systematics), which allows us to study residual
systematics. On scales larger than 10 arcminutes, we find no ``B''-mode. On
smaller scales we find a small, but significant ``B''-mode. This signal is also
present when we select a sample of bright galaxies. These galaxies are rather
insensitive to observational distortions, and we therefore conclude that the
oberved ``B''-mode is likely to be caused by intrinsic alignments. We therefore
limit the cosmic shear analysis to galaxies with 22<R_C<24. We derive joint
constraints on Omega_m and sigma_8, by marginalizing over Gamma, Omega_Lambda
and the source redshift distribution, using different priors. We obtain a
conservative constraint of
(95% confidence). A better constraint is derived when we use Gaussian priors
redshift distribution. For this choice of priors, we find
(95% confidence). Using our
setof Gaussian priors, we find that we can place a lower bound on Gamma:
Gamma>0.1+0.16\Omega_m$ (95% confidence). Comparison of the RCS results with
three other recent cosmic shear measurements shows excellent agreement. The
current weak lensing results are also in good agreement with CMB measurements,
when we allow the reionization optical depth tau and the spectral index n_s to
vary. We present a simple demonstration of how the weak lensing results can be
used as a prior in the parameter estimation from CMB measurements to derive
constraints on the reionization optical depth tau. (abridged)Comment: 9 pages, 6 figures, Accepted for publication in the Astrophysical
Journa
- âŠ