Professor Gerrit Verschuur, University of Memphis

"Associations between Galactic HI and WMAP Small-Scale Structure"

Abstract:
Spatial associations have been found between interstellar neutral
hydrogen (HI) emission morphology and small-scale structure observed 
by the Wilkinson Microwave Anisotropy Probe (WMAP) in an area bounded by 
l = 60 & 180, b = 30 & 70 degrees, which is marked by the presence of highly 
disturbed local HI and a preponderance of intermediate- and high-velocity gas.
The HI distribution toward the brightest peaks in the WMAP Internal
Linear Combination (ILC) map for this area is examined and by
comparing with a second area on the sky it is demonstrated that the
associations do not appear to be the result of chance coincidence.
Close examination of several of the associations reveals important
new properties of diffuse interstellar neutral hydrogen structure. In
the case of high-velocity cloud MI, the HI and ILC morphologies are
similar and an excess of soft X-ray and H-alpha emission have been
reported for this feature. A prediction regarding what is likely to
be found toward HVC MII is confirmed.  Overall, the data suggest that
the small angular-scale structure observed by WMAP is produced at the
interface between HI features interacting with one another, or at the
interface between moving HI structures and regions of enhanced plasma
density in the surrounding interstellar medium.  Examples of the
apparent associations will be shown without offering an unambiguous
explanation as to the relevant emission mechanism(s).   A preview of
a number of dramatic associations already noted in the southern
galactic hemisphere will also be offered.