Abstract
The evidence for microwave emission from spinning dust grains has been strengthened considerably by its detection in a number of discrete astrophysical objects associated with star formation. These detections, in combination with statistical constraints on its presence on large angular scales in the diffuse ISM, have provided strong observational confirmation of an emission mechanism still referred to as anomalous. This emission has a peaked spectrum with a maximum in the microwave band; the present review discusses the continuum radio emission mechanisms which can contribute to this region of the electromagnetic spectrum, collects published results on the prevalence of anomalous microwave emission in a variety of star formation regions, presents the overall conclusions that may be drawn from the detections so far, and discusses the prospects for future research on the anomalous microwave emission attributed to spinning dust within star forming regions.
Highlights
The interstellar medium (ISM) of our galaxy and others is volume dominated by a small number of components
Between them these components make up three phases, where they exist with densities regulated by pressure equilibrium: the hot phase of the hot ionized medium (HIM), the cooler combined warm phase of the warm ionized medium (WIM) and warm neutral medium (WNM), and the cold cold neutral medium (CNM) phase [4]
Of the seven different environments considered as possible sites for producing spinning dust emission by Draine and Lazarian [13], three are representative of the large scale diffuse interstellar medium or cirrus: the cold neutral medium (CNM), the warm neutral medium (WNM), and the warm ionized medium (WIM); five are directly associated with star formation: dark clouds, molecular clouds, the warm ionized medium, reflection nebulae, and photodissociation regions
Summary
The interstellar medium (ISM) of our galaxy and others is volume dominated by a small number of components. Hii regions themselves have electron densities that range 1–105 cm−3, far higher than those of the WIM With such high densities and large thermal velocities, these Hii regions often cause otherwise collapsing clouds to expand into the ambient ISM, tearing apart the larger gravitationally bound molecular cloud. Star formation regions are generally studied at much shorter wavelengths, the identification of such regions with anomalous microwave emission attributed to spinning dust has led to a surge of observational studies at radio-microwave frequencies These studies concentrate on small angular scales where radio emission is known historically to be associated with protostellar objects, and on the extended scales of the clouds which contain this activity and the wider complexes of such clouds.
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