Observations of Anomalous Microwave Emission from HII regions

TL;DR

This review summarizes observations of Anomalous Microwave Emission (AME) from HII regions, highlighting detection challenges, potential emission sources, and the need for more high-resolution, high-frequency data to clarify emission mechanisms.

Contribution

It provides a comprehensive summary of AME observations in HII regions and discusses the complexities and uncertainties in current measurements and interpretations.

Findings

AME detected near HII regions but confirmation needs more data.

Optically thick free-free emission from UCHII regions may contribute significantly.

AME emissivity varies with dust temperature and environment.

Abstract

In this brief review, I give a summary of the observations of Anomalous Microwave Emission (AME) from HII regions. AME has been detected in, or in the vicinity of, HII regions. Given the difficulties in measuring accurate SEDs over a wide range of frequencies and in complex environments, many of these detections require more data to confirm them as emitting significant AME. The contribution from optically thick free-free emission from UCHII regions may be also be significant in some cases. The AME emissivity, defined as the ratio of the AME brightness to the 100 micron brightness, is comparable to the value observed in high-latitude diffuse cirrus in some regions, but is significantly lower in others. However, this value is dependent on the dust temperature. More data, both at high frequencies (>5 GHz) and high resolution (~1 arcmin or better) is required to disentangle the emission processes in such complex regions.