Diffuse galactic emission from dust grains

Experiments to measure anistropies in the cosmic background radiation have discovered a new “anomalous” component of galactic emission in the 15–90 GHz region. This component is correlated with interstellar dust, but has an intensity and spectrum very different from what interstellar dust had been expected to emit at these frequencies. The “anomalous emission” has been interpreted by the some as free-free emission, but free-free emission from interstellar plasma cannot possibly be this strong. The “anomalous emission” can be quite naturally explained as the “rotational” emission from the population of ultrasmall dust grains which is independently required by observations of 3–60 μm diffuse infrared emission. Alternatively, some of the observed 15–90 GHz emission could be due to magnetic dipole emission from magnetic materials in interstellar grains. Experiments to distinguish between these two emission processes are discussed.

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