Constraints on free-free emission from Anomalous Microwave Emission Sources in the Perseus Molecular Cloud

TL;DR

This study uses Green Bank Telescope observations at 1.4 and 5 GHz to constrain free-free emission in the Perseus molecular cloud, confirming that the 33 GHz anomalous emission exceeds low-frequency contributions.

Contribution

The paper provides new upper limits on free-free emission at low frequencies, demonstrating that the 33 GHz emission is not explained by free-free processes, confirming its anomalous nature.

Findings

No significant extended emission detected at 1.4 and 5 GHz.

Upper limits on free-free contribution are 27%, 12%, and 18%.

Low frequency emission is not spatially correlated with 33 GHz emission.

Abstract

We present observations performed with the Green Bank Telescope at 1.4 and 5 GHz of three strips coincident with the anomalous microwave emission features previously identified in the Perseus molecular cloud at 33 GHz with the Very Small Array. With these observations we determine the level of the low frequency (~1 - 5 GHz) emission. We do not detect any significant extended emission in these regions and we compute conservative 3\sigma upper limits on the fraction of free-free emission at 33 GHz of 27%, 12%, and 18% for the three strips, indicating that the level of the emission at 1.4 and 5 GHz cannot account for the emission observed at 33 GHz. Additionally, we find that the low frequency emission is not spatially correlated with the emission observed at 33 GHz. These results indicate that the emission observed in the Perseus molecular cloud at 33 GHz, is indeed in excess over the low frequency emission, hence confirming its anomalous nature.