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Missing Baryons in Galaxies

by Joel Bregman (University of Michigan, US)

Nov 13, 2014 from 02:00 PM to 03:30 PM

Where Seminars' room, floor -1, via Ranzani 1

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Galaxies are missing most of their baryons in that the ratio of the dark matter to the star and gas masses in the optical galaxy is much larger than the cosmological value. This census does not include halo gas, which is predicted to exist from galaxy formation models, although the hot gas mass is model-dependent. Our program includes the search for the faint X-ray emission from million degree halos that are in approximate hydrostatic equilibrium with the gravitational field. We detect extended X-ray emitting gas and the mass within R_200 can be comparable to the stellar mass but still falls far short of the missing baryons. The baryons are no longer “missing" if the halo gas extends to 3-5 R_200, which implies that the gas is unbound. The S-Z measurements from Planck supports the picture where most of the baryons are indeed hot.