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Prof R. Brent Tully (Institute for Astronomy, University of Hawaii)

Squelched Galaxies and Dark halos - Prof R. Brent Tully Colloquium

The Australia Telescope National Facility Colloquium
15:30-16:30 Wed 03 Dec 2003

ATNF Marsfield Lecture Theatre


According to the Cold Dark Matter hierarchical clustering
paradigm, there should be many more low mass halos than
massive halos. However the frequency of dwarf galaxies
is not high enough to meet these expectations. There is
increasingly good evidence that the deficiency with
respect to expectations depends on environment, with
greater deficiencies at lower densities. Possibly the
cause is related to constraints on the ability of low
mass halos to accummulate baryons at the epoch of collapse.
If the baryons are hot, as they would be after reionization,
then they contain too much thermal energy to be trapped in
low mass potential wells. Accordingly, only early-forming
dwarfs would gather baryons such that they become visible
and most low mass dark halos would be devoid of gas and

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