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The Missing Baryons and the Cosmic Microwave Background

Carlos Hernandez Monteagudo
MPA, Germany

The amount of baryons seen in the local Universe falls short by a factor 2-5 if  compared to the amount of detected baryons at intermediate (z~5) or high  (z~1,100) redshift. This is the so called "missing baryon" problem in Cosmology. Hydrodynamical  simulations of the large scale structure predict that most of those missing baryons  should be in the form of ionized gas present in slightly overdense regions, at a temperature ranging from 10^5 to 10^7 K, conforming the "Warm Hot Intergalactic  Medium" (WHIM).

This WHIM would not form stars, and would not emit or absorb either in the IR,  optical or UV. However, it should interact with the photons of the Cosmic  Microwave  Background (CMB) through two different channels: (i) Thompson scattering (where  there is no energy exchange) and (ii) Compton scattering (where hot electrons transfer energy to the CMB photons, distorting their black body spectrum).

I shall review the status of the search for missing baryons in the context of CMB observations and the currently most favored cosmological model. I shall also outline  new methods and prospects for detecting this missing gas with upcoming CMB  experiments and address the link between the cosmic baryon problem and the search for (so far undetected) bulk flows at scales of ~20 Mpc/h.

2009 January 14, 13:30

Centro de Astrofísica da Universidade do Porto (Auditorium)
Rua das Estrelas, 4150-762 Porto

Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia