My guess is that it's a result of something obscuring the view (or otherwise lengthening wavelength, lowering the effective temperature, reducing the wavelength, etc) not a giant gap in space.
The paper doesn't seem to have been published yet but you can get the preprint at:
http://lanl.arxiv.org/PS_cache/arxiv/pdf/0704/0704.0908v2.pdf
Oh Los Alamos, what can't you do?