Universities Space Research Association | Arecibo Observatory | 2017 Jan 04
Arecibo Observatory observations of galactic neutral hydrogen structure confirm the discovery of an unexpected contribution to the measurements of the cosmic microwave background observed by the WMAP and Planck spacecraft. An accurate understanding of the foreground (galactic) sources of radiation observed by these two spacecraft is essential for extracting information about the small-scale structure in the cosmic microwave background believed to be indicative of events in the early universe.
The new source of radiation in the 22 to 100 GHz range observed by WMAP and Planck appears to be emission from cold electrons (known as free-free emission). While cosmologists have corrected for this type of radiation from hot electrons associated with galactic nebulae where the source temperatures are thousands of degrees, the new model requires electron temperatures more like a few 100 K.
The spectrum of the small-scale features observed by WMAP and Planck in this frequency range is very nearly flat -- a finding consistent with the sources being associated with the Big Bang. At first glance it appears that the spectrum expected from the emission by cold galactic electrons, which exist throughout interstellar space, would be far too steep to fit the data. However, if the sources of emission have a small angular size compared with the beam width used in the WMAP and Planck spacecraft, the signals they record would be diluted. The beam widths increase with lower frequency, and the net result of this "beam dilution" is to produce an apparently flat spectrum in the 22 to 100 GHz range. ...
On the Nature of Small-Scale Structure in the Cosmic Microwave Background Observed by Planck and WMAP - G. L. Verschuur, J. T. Schmelz
- Astrophysical Journal 832(2):98 (2016 Dec 01) DOI: 10.3847/0004-637X/832/2/98