Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.mrao.cam.ac.uk/~anthony/latex/Wilkinson.ps Дата изменения: Sun Jun 25 15:54:30 2000 Дата индексирования: Tue Oct 2 03:50:52 2012 Кодировка: Поисковые слова: manicouagan crater

Constraints on mass clumps in the Universe
P.N. Wilkinson et al.
University of Manchester, Jodrell Bank Observatory, U.K.
Over the past decade large radio surveys for strong gravitational
lensing have been carried out. Radio observations are particularly
well suited to making complete and unbiased searches since they
are not aected by extinction and have similar resolution and sen-
sitivity for all the sources in a sample. The Caltech-Jodrell Bank
VLBI Surveys (CJ{300 objects) are sensitive to the angular size
range 1.5-50 milliarcsec ( 10 5:5 10 8:5
M ); the Jodrell-VLA As-
trometric Survey (JVAS{2300 objects) and the Cosmic Lens All
Sky Survey (CLASS{12000 objects) are sensitive from  0:1 to 30
arcsec ( 10 9 10 14 M ) while the Arcminute Radio Cluster Sur-
vey (ARCS{1200 objects) covers the range from 25 to 60 arcsec
( 10 15 M ). So far, however, strong lensing has only been seen
in the JVAS/CLASS surveys and then only for a narrow range of
angular sizes around 1 arcsec corresponding to the mass of the
central regions of large galaxies. The narrowness of the galaxy-
mass lenses places important constraints on theories of galaxy
formation. The well-dened failure to detect strong lensing in all
the other size ranges allows us to place unique constraints on the
amount of clumpy matter (dark or otherwise) in the universe. In
particular the failure to detect millilensing places a strong up-
per limit of  2% of the closure density on compact objects of
 10 6 M and rules out models involving large population of pre-
galactic black holes. Our failure to detect any cluster{mass lenses
is beginning to have an impact on large-scale cluster formation.
Co-authors: The CJ, JVAS/CLASS and ARCS teams
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