Anomalous Microwave Emission: Theory, Modeling, and Observations

Abstract

Anomalous Microwave Emission (AME) was first identified in the late 1990s, through sensitive high frequency radio CMB observations. The usual emission mechanisms (e.g., blackbody, synchrotron, and free-free) did not appear to be able to account for the excess emission in the frequency range 10– 60GHz. Since then, a large body of observational evidence has emerged showing that AME appears to be emitted both in the diffuse interstellar medium at large, and from specific clouds within our galaxy. Detections from star-forming regions in an external galaxy have also been made. Nevertheless, detailed measurements have been difficult due to the frequency range (difficult to observe from the ground) and confusion with other emission mechanisms that emit in this frequent range. The most promising candidate for the AME is electric dipole radiation from small spinning dust grains (spinning dust emission). This was first predicted in the late 50s, with major developments in the theory over the last 15 years. The theory predicts a peaked spectrum which emits at frequencies from about 10GHz to over 100GHz, but with a wide range of peak frequencies and emissivities, which depend on the local environment and dust grain size distribution. There is still significant debate about the true nature of the AME, and both observations and theory are still relatively unexplored. An exciting possibility is to use detailed radio observations of spinning dust to study the interstellar medium, in a complementary way to the optical, UV, and infrared domains. This special issue is dedicated to the study of AME.