The Discovery of Anomalous Microwave Emission

We discuss the first detection of anomalous microwave emission, in theOwens Valley RING5M experiment, and its interpretation in the contextof the ground-based cosmic microwave background (CMB) experiments ofthe early 1990s. The RING5M experiment was one of the first attemptsto constrain the anisotropy power on sub-horizon scales, by observinga set of -size fields around the North Celestial Pole (NCP). Fields were selected close to the NCP to allow continuous integrationfrom the Owens Valley site. The experiment detected significantemission at both 14.5 GHz and 30 GHz, consistent with a mixture of CMBand a flat-spectrum foreground component, which we termed anomalous, as it could be explained neither by thermal dust emission,nor by standard models for synchrotron or free-free emission. Asignificant spatial correlation was found between the extractedforeground component and structure in the IRAS 100 μm maps. While microwave emission from spinning dust may be the most naturalexplanation for this correlation, spinning dust is unlikely to accountfor all of the anomalous emission seen in the RING5M data