On the Apparent Associations between Interstellar Neutral Hydrogen
  Structure and (WMAP) High Frequency Continuum Emission
  Galactic neutral hydrogen (HI) within a few hundred parsecs of the Sun
contains structure with an angular distribution that is similar to small-scale
structure observed by the Wilkinson Microwave Anisotropy Probe (WMAP). A total
of 108 associated pairs of associated HI and WMAP features have now been
cataloged using HI data mapped in 2 km/s intervals and these pairs show a
typical offset of 0.8 degrees. A large-scale statistical test for a direct
association is carried out that casts little additional light on whether the
these small offsets are merely coincidental or carry information. To pursue the
issue further, the nature of several of the features within the foreground HI
most closely associated with WMAP structure are examined in detail and it is
shown that the cross-correlation coefficient for well-matched pairs of
structures is of order unity. It is shown that free-free emission from
electrons in unresolved density enhancements in interstellar space could
theoretically produce high-frequency radio continuum radiation at the levels
observed by WMAP and that such emission will appear nearly flat across the WMAP
frequency range. Evidence for such structure in the interstellar medium already
exists in the literature. Until higher angular resolution observations of the
high-frequency continuum emission structure as well as the apparently
associated HI structure become available, it may be difficult to rule out the
possibility that some if not all the small-scale structure usually attributed
to the cosmic microwave background may have a galactic origin.
