A Case Against Spinning PAHs as the Source of the Anomalous Microwave Emission

TL;DR

This study challenges the spinning PAH hypothesis for AME by analyzing all-sky microwave data, revealing that AME correlates with dust radiance but not with PAH emission, and showing inconsistencies with existing models.

Contribution

The paper provides observational evidence against PAHs as the primary source of AME, suggesting alternative carriers like ultrasmall silicates or magnetic dipole emission.

Findings

AME correlates best with dust radiance.

No correlation between AME fluctuations and PAH emission.

AME increases with radiation field strength, contrary to spinning dust predictions.

Abstract

We employ an all-sky map of the anomalous microwave emission (AME) produced by component separation of the microwave sky to study correlations between the AME and Galactic dust properties. We find that while the AME is highly correlated with all tracers of dust emission, the best predictor of the AME strength is the dust radiance. Fluctuations in the AME intensity per dust radiance are uncorrelated with fluctuations in the emission from polycyclic aromatic hydrocarbons (PAHs), casting doubt on the association between AME and PAHs. The PAH abundance is strongly correlated with the dust optical depth and dust radiance, consistent with PAH destruction in low density regions. We find that the AME intensity increases with increasing radiation field strength, at variance with predictions from the spinning dust hypothesis. Finally, the temperature-dependence of the AME per dust radiance disfavors the interpretation of the AME as thermal emission. A reconsideration of other AME carriers, such as ultrasmall silicates, and other emission mechanisms, such as magnetic dipole emission, is warranted.