2007ApJ...671..447V

Spatial associations have been found between interstellar neutral hydrogen (H I) emission morphology and small-scale structure observed by the Wilkinson Microwave Anisotropy Probe (WMAP) in an area bounded by l=60°, 180° and b=30°, 70°, which was the primary target for this study. This area is marked by the presence of highly disturbed local H I and a preponderance of intermediate- and high-velocity gas. The H I 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 the high-velocity cloud MI, the H I and WMAP ILC morphologies are similar, and an excess of soft X-ray emission and Hα emission have been reported for this feature. It is suggested that the small angular scale, high-frequency continuum emission observed by WMAP may be produced at the surfaces of H I features interacting one another, or at the interface between moving H I structures and regions of enhanced plasma density in the surrounding interstellar medium. It is possible that dust grains play a role in producing the emission. However, the primary purpose of this report is to draw attention to these apparent associations, without offering an unambiguous explanation as to the relevant emission mechanism(s).