JOINT
ASTROPHYSICS/JOINT PARTICLE SEMINAR
Date:
Tuesday, 24 February
2004
Time:
4:00 pm
Place:
1114 Nat. Sci. 1
Speaker:
James Bullock, CfA, Harvard
Title:
"Cosmology and the Milky Way"
Abstract: If the favored Cold Dark Matter
(CDM) model of structure formation is correct, then
the first objects to collapse in the
Universe are low-mass systems, which fall
together to form progressively larger structures over
time. Our Galaxy system, for example,
should have accreted and subsequently tidally destroyed
~100 low-mass galaxies in the past ~12 Gyr. The roughly 10
satellite galaxies we see around the Milky Way today correspond
to the residual, surviving population of these
early-collapse objects. Put in
this context, near-field observations of the Milky
Way and its environment offer a powerful probe of cosmology
and galaxy formation on small scales and at early
times. I discuss a program to simulate the formation of the Milky
Way system within the context the LCDM "concordance"
cosmological model. One interesting result is that the
debris from accreted, disrupted, low-mass galaxies should produce
an extended stellar cloud of material about the main galaxy that has
similar characteristics to the observed "stellar halo" component
of our Milky Way. A stellar halo formed in this
manner should be dominated by spatially coherent substructure at
large radii, and this should be detectable by
several ongoing and upcoming surveys.
Searches of this kind offer a direct test of
whether cosmology is indeed hierarchical
on small scales, where the current paradigm is facing its most
serious challenges. More generally, Galactic
observations help test ideas about star formation in
early-forming, low-mass galaxies and are sensitive to the shape
of the initial inflationary power spectrum and to the
nature of dark matter..
Host:
G. Chanan