Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gravitational `Convergence' and Cluster Masses   Two colour photometry of the cluster A1689 reveals a `relative
magnification-bias' between lensed blue and red background galaxies, arising
from a dependence of the faint galaxy count-slope on colour. The colour
distribution is skewed blueward of the far field, allowing us to measure the
cluster magnification and to understand the notorious blueness of large arcs.
We show that the magnification information can be combined with the usual image
distortion measurements to isolate the local `convergence' component of lensing
and hence derive the projected mass. This is achieved through a simple local
relation between the convergence and the observables, which can be applied
generally over the surface a cluster. In the weak lensing limit, the
convergence reduces to a dependence on the magnification alone, so that in the
outskirts of clusters the surface-density of matter is obtained directly from
the surface-density of background galaxies. Hence, useful lensing work requires
colour information but not necessarily good seeing. Interestingly, convergence
varies slowly at high redshift, saturating at a level depending on the Horizon
distance, allowing a useful model-independent measurement of the Global
Geometry.

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The categories of this paper are: patt-sol
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The categories of this paper are: eess
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The categories of this paper are: nlin
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The categories of this paper are: hep-ex
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The categories of this paper are: math
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The categories of this paper are: nucl-ex
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The categories of this paper are: gr-qc
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The categories of this paper are: cond-mat
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The categories of this paper are: atom-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: cs
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-ph
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The categories of this paper are: math-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: q-alg