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Astrophysics Colloquium

Missing Baryons in Galaxies
Presented by Joel Bregman
Department of Astronomy, University of Michigan

Thursday, February 12, 2015
4:00 P.M. in 169-336

Abstract
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.

JPL Contact: Olivier Dore (4-0690)


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