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Situation
and
the
scientific
objectives
The
current
standard model
of galaxy
formation is
crossing a
crisis: the
dark matter is
predicted to
collapse in
the center of
galaxies,
baryons lose
their angular
momentum
through
dynamical
friction
against dark
matter, and
each halo of
Milky Way type
should be
surrounded by
thousands of
unseen dark
satellites.
Are the
baryonic
physical
processes
(star
formation,
feedback,
active
galactic
nuclei..) able
to modify
sufficiently
the
distribution
of dark
matter, and
solve the
various
problems?
Massive
galaxies are
forming
most of
their stars
early in the
universe,
while the
present
starbursts are
occurring
mainly in
dwarfs, is
this
incompatible
with the
hierarchical
scenario?
Direct
observations
at high
redshift, and
numerical
simulations
have
made large
progress in
recent years,
and it should
be fruitful to
confront both
in order that
possible
solutions to
the problems
emerge.
Previously
regarded
simply as a
prediction of
general
relativity,
nowadays
gravitational
lenses are a
valuable tool
in astronomy.
When strong,
they act like
a telescope,
by amplifying
enough the
image of
distant
galaxies to
make them
detectable.
When
weak,
they can be
efficient in
statistical
studies to
trace mass in
the universe,
and mainly the
one of dark
matter. They
can be used to
enlighten
fundamental
problems; for
example, the
equation of
state of dark
energy is now
a main clue to
allow the
determination
of
cosmological
parameters, or
the nature of
the first
galaxies,
which requires
a
high-resolution
study.
Catalogs from
deep fields at
high
resolution
(COSMOS, ...)
as well as
those
corresponding
to larger
fields but
lower
resolution
(CFHTLS,
Terapix, ..),
have shown
that we can
detect the
distribution
of dark matter
at different
scales around
the clusters
and voids. In
the case of
individual
clusters,
strong lensing
has allowed a
clearer
determination,
which can be
compared to
the
dark-matter
distribution
derived from
X-rays.
Towards
individual
galaxies, the
only method is
to stack of a
large number
of them, of
the same type,
or derive
statistical
properties.
This school
will cover the
study and use
of
gravitational
lenses at all
scales
(cosmological,
that of galaxy
clusters, and
galaxies), so
to highlight
the shape and
extent of dark
matter halos
around
structures
(clusters,
galaxies of
all types). It
provides an
opportunity
for theorists
and observers
to discuss by
confronting
data with
theories. We
can also
compare the
properties of
dark matter
relative to
those of
baryons.
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