Microwave observations of spinning dust emission in NGC 6946

Abstract

We report new cm-wave measurements at five frequencies between 15 and 18 GHz of thecontinuum emission from the reportedly anomalous ‘region 4’ of the nearby galaxyNGC6946.We find that the emission in this frequency range is significantly in excess of that measuredat 8.5 GHz, but has a spectrum from 15 to 18 GHz consistent with optically thin free–freeemission from an ultracompact HII region. In combination with previously published data,we fit four emission models containing different continuum components using the Bayesianspectrum analysis package RADIOSPEC. These fits show that, in combination with data at otherfrequencies, a model with a spinning dust component is slightly preferred to those that possessbetter-established emission mechanisms.