Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-12-13
Astrophys.J.680:1235-1242,2008
Astronomy and Astrophysics
Astrophysics
8 pages, 5 figures; submitted to ApJ; LaTeX modified slightly to reveal missing Figure 5
Scientific paper
10.1086/587863
CMB experiments commonly use maps of Halpha intensity as a spatial template for Galactic free-free emission, assuming a power law I_nu \propto nu^-0.15 for the spectrum. Any departure from the assumed free-free spectrum could have a detrimental effect on determination of the primary CMB anisotropy. We show that the Halpha-correlated emission spectrum in the diffuse warm ionized medium (WIM) is not the expected free-free spectrum at WMAP frequencies. Instead, there is a broad bump in the spectrum at ~50 GHz which is consistent with emission from spinning dust grains. Spectra from both the full sky and smaller regions of interest are well fit by a superposition of a free-free and WIM Draine & Lazarian (1998) spinning dust model, shifted in frequency. The spinning dust emission is ~5 times weaker than the free-free component at 50 GHz, with the null hypothesis that the Halpha-correlated spectrum is pure free-free, ruled out at >8 sigma in all regions and >100 sigma for the full sky fit.
Dobler Gregory
Finkbeiner Douglas Paul
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