Microwave emission from dust revisited (Research Note)

Context. The origin of the anomalous microwave emission is not yet identified but it may be associated with (spinning) dust. Aims. We point out that the emission from low-energy, solid-state structural transitions, apparent over a range of dust temperatures, and particularly important at low dust temperatures (T(d) < 30K), could provide an origin for the excess microwave emission. Methods. The physics of two-level systems (TLS) within amorphous materials is applied within the context of interstellar dust. Results. TLS systems, which are thought to be at the origin of the temperature-dependent emissivity of interstellar dust, should reveal their existence at long wavelengths in the emission from dust. Conclusions. Low-energy, structural transitions in amorphous interstellar grains could make a contribution to the anomalous microwave emission, which should correlate with the emission from dust components with temperatures less than about 30K.