Mapping The Dark Universe

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Welcome to the IGM research wiki at the University of Chicago. The primary objective of the research is to characterize and understand the evolution and recycling of baryons.

A traditional approach to study the formation and evolution of the large scale structures is to carry out a deep galaxy survey over a large volume. The number density of galaxies and their clustering amplitude as a function of time constrain the history of stellar mass assembly and their bias w.r.t. the underlying dark matter halos. The Hubble Ultra Deep Field has recorded the deepest image of the universe, unveiling both the exquisite details of distant galaxies and the vast empty intergalactic space.

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Stars make up roughly 10-15% of the total baryons there are in the present-day universe. Including atomic gas observed in 21cm surveys and hot x-ray gas observed in galaxy clusters, we can still account for only 1/3 of the total baryons. This "dark" baryon fraction is higher during earlier epochs. The accounting indicates that a dominant fraction of bayrons are invisible in surveys that search for photon emission.


Using a distant luminous source, such as a quasar or optical afterglow of a γ-ray burst, we can study the baryon content of the dark universe through the absorption features imprinted by intervening (otherwise) invisible clouds in the spectrum of the background source.

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Distant quasars have served as a sensitive probe of intervening gas at redshift as high as the quasars can be found. As the photons from the background quasars travel through intergalactic space, they are expected to be reprocessed by intervening gaseous clouds along the line of sight through scattering and/or absorption. In turn, these intervening clouds are expected to imprint absorption features in the spectra of background quasars. Detailed absorption-line studies in the number densities of intervening clouds, their thermal and ionization states versus time, and the underlying chemical abundances have uncovered a wealth of information in the physical properties of the intergalactic medium.

Details of on-going research projects are described here.