University of Waterloo
200 University Avenue West
Waterloo, Ontario, Canada N2L 3G1
Phone: (519) 888-4567 ext 32215
Fax: (519) 746-8115
University of Michigan
Joel Bregman applies his expertise in X-ray observation and theory to account for the “missing baryons” (normal matter) in galaxies.
The Cosmic Microwave Background measurements gives a precise ratio of the dark matter to baryonic matter and the mean cosmological density of baryons. At low redshift, about half of the baryons are unaccounted for (“missing”), and in individual galaxies, the missing baryon problem is more extreme. A solution is offered by models of structure and galaxy formation, such as a significant mass in dilute hot halos that extend out to, or beyond the virial radius. We have used X-ray observations to detect and study these hot halo and find that they provide an important mass reservoir for future generations of star formation through “hot mode” accretion. However, these hot halos do not account for the missing baryons in galaxies unless they extend well beyond the virial radius, which implies strong galactic feedback.