The discovery
of a new class of gravitational lenses, the groups of galaxies, by an
international team of astronomers using the Canada-France-Hawaii Legacy
Survey
(CFHTLS), comes 20 years after the publication in January 1987 of the
first
image of a gravitational arc, made also at CFHT with one of the first
CCD
cameras in operation at an observatory. This discovery of gravitational
arcs in
the center of galaxy groups is an important step in our understanding
of the
large scale structures of the universe. These
new results will allow a better understanding of the distribution of
the dark
matter and the formation mechanisms of the groups of galaxies,
structures intermediate in mass between galaxies
and
clusters of galaxies.
Up to recently, only the most massive galaxy clusters
and the massive galaxies were the object of gravitational lensing
studies.
Intermediate-scale structures like the galaxy groups should however be
looked
in order to better understand the evolution of the structures in the
Universe.
Since the arrival of the MegaCam camera in 2003 on
Megaprime, the new CFHT prime focus, astronomers have been able to
observe at
once a large area of the sky (1 square degree or 4 Full Moon) in 340
MegaPixel
digital images with an unprecedented resolution for such a field of
view. The
Canadian and French communities decided to pull their resources
together and to
devote 500 nights of telescope time over five years to a large project,
the
CFHT Legacy Survey, which will cover around 1% of the sky visible from
Thanks to a careful inspection aimed at detecting
gravitational arcs in one fourth of the CFHTLS, the team has been able
to
detect for the first time numerous arcs around galaxy groups. This
unexpected
discovery provides for the first time direct information on the
structure of galaxy
groups which are key environments in the formation of structures in the
Universe. Scientists will be able to understand the role of dark matter
in the
evolution of these groups and of the mass concentrations that make the
large
structures of the Universe.
Images of some of the newly discovered
arc systems, as
well as historical pictures of the first observation of a gravitational
arc, are
available here:
www.cfht.hawaii.edu/News/StrongLensing/
Contacts in France:
Remi Cabanac – Observatoire Midi-PyreneesJean-Paul Kneib – Laboratoire d'Astronomie de MarseilleContact at CFHT:
Jean-Francois Sygnet - Institut d'Astrophysique de Paris
Christian Veillet - 1 (808) 885 2143 or 1 (808) 938 3905