Observations of Free-Free and Anomalous Microwave Emission from LDN 1622 with the 100 m Green Bank Telescope

TL;DR

This study uses high-resolution radio observations to analyze free-free and anomalous microwave emissions from LDN 1622, confirming the spinning dust model as a natural explanation for the observed AME at 13.7 GHz.

Contribution

First high-resolution mapping of LDN 1622 at 4.85 and 13.7 GHz, linking radio emissions with infrared data and supporting the spinning dust model for AME.

Findings

Free-free emission corona surrounds LDN 1622

Measured AME flux density at 13.7 GHz is 7.0 ± 1.4 mJy

Evidence of rising spectrum between 13.7 GHz and 31 GHz

Abstract

LDN 1622 has previously been identified as a possible strong source of dust-correlated Anomalous Microwave Emission (AME). Previous observations were limited by resolution meaning that the radio emission could not be compared with current generation high-resolution infrared data from Herschel, Spitzer or WISE. This Paper presents arcminute resolution mapping observations of LDN 1622 at 4.85 GHz and 13.7 GHz using the 100 m Robert C. Byrd Green Bank Telescope. The 4.85 GHz map reveals a corona of free-free emission enclosing LDN 1622 that traces the photo-dissociation region of the cloud. The brightest peaks of the 4.85 GHz map are found to be within 10% agreement with the expected free-free predicted by SHASSA H{\alpha} data of LDN 1622. At 13.7 GHz the AME flux density was found to be 7.0 $\pm$ 1.4 mJy and evidence is presented for a rising spectrum between 13.7 GHz and 31 GHz. The spinning dust model of AME is found to naturally account for the flux seen at 13.7 GHz. Correlations between the diffuse 13.7 GHz emission and the diffuse mid-infrared emission are used to further demonstrate that the emission originating from LDN 1622 at 13.7 GHz is described by the spinning dust model.