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This Week at Physics

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Event Number 3507

  Friday, October 17th, 2014

Special Astronomy Talk
"The Structure of the Faintest Dwarf Galaxies"
Time: 12:00 pm
Place: 4421 Sterling Hall
Speaker: Ken Freeman, ANU College of Physical and Mathematical Sciences
Abstract: The faintest dwarf galaxies are very baryon-depleted and have large
M/L ratios. Their gravitational fields are dominated by their dark halos.
If the dark halos have cores of near-constant surface density, and the
baryons have isotropic kinematics and are close to isothermal as observed,
then the density distribution of the baryons is expect to have a simple
analytic form which we can use to measure the central densities of their
dark halos. The observed density distributions of the faintest dwarf
spheroidal and dwarf irregular galaxies appear to follow this expected

The core radii and central densities of the dark halos of rotationally
dominated late-type spirals scale with their absolute magnitudes: the
densities decrease with luminosity and the core radii increase, with
the central surface densities of the halos being almost independent of
lumiosity. I will talk about the consequences of these scaling laws and
some other correlations for the epoch of formation of the dwarfs, the
sizes of their dark halos and the existence of dark dwarfs.
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