Microwave observations of spinning dust emission in NGC 6946☆

We report new cm-wave measurements at five frequencies between 15 and 18 GHz of the continuum emission from the reportedly anomalous 'region 4' of the nearby galaxy NGC 6946. We find that the emission in this frequency range is significantly in excess of that measured at 8.5 GHz, but has a spectrum from 15 to 18 GHz consistent with optically thin free-free emission from an ultracompact H ii 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.