Astronomy Colloquium / Fall 2008

September 10

Prof. Michael Shull

University of Colorado

Baryons and Metals in the low-redshift Intergalactic Medium and Galactic Halo

Far-ultraviolet spectra of quasars and other active galaxies from the Hubble Space Telescope (HST) and Far-Ultraviolet Spectroscopic Explorer (FUSE) have allowed astronomers to probe baryons and heavy elements in the low-redshift intergalactic medium (IGM) as well as the Galactic halo. These UV surveys have identified approximately half the baryons inferred from Big Bang nucleosynthesis and the Cosmic Microwave Background, in the form of diffuse Lya absorbers and hot ionized gas (OVI). This OVI-bearing gas, at temperatures of 105 to 106 K, may be produced by shocks during the formation of large-scale structure and by powerful galactic outflows. The Cosmic Origins Spectrograph (COS) to be installed on HST in Oct 2008 will probe the IGM content and evolution out to redshift z = 1. Our key science includes studies of missing baryons, metal evolution and transport, intervening galaxy halos, and cosmology, with over 104 Lyman alpha absorbers and corresponding metal lines at low redshift.