Microwave observations of spinning dust emission in NGC6946

TL;DR

This study presents new centimeter-wave observations of NGC6946, revealing excess emission consistent with spinning dust, and uses Bayesian analysis to compare emission models, favoring the spinning dust hypothesis.

Contribution

First detection of potential spinning dust emission in NGC6946 using multi-frequency radio data and Bayesian spectral fitting.

Findings

Excess emission at 15-18 GHz suggests spinning dust presence.

Bayesian analysis slightly favors spinning dust model over others.

Emission consistent with optically thin free-free from a compact HII region.

Abstract

We report new cm-wave measurements at five frequencies between 15 and 18GHz of the continuum emission from the reportedly anomalous "region 4" of the nearby galaxy NGC6946. We find that the emission in this frequency range is significantly in excess of that measured at 8.5GHz, but has a spectrum from 15-18GHz consistent with optically thin free-free emission from a compact HII region. In combination with previously published data we fit four emission models containing different continuum components using the Bayesian spectrum analysis package radiospec. These fits show that, in combination with data at other frequencies, a model with a spinning dust component is slightly preferred to those that possess better-established emission mechanisms.