2025MNRAS.536.2914H

Anomalous microwave emission (AME) is a major component of Galactic emission in the frequency band 10-60 GHz and is commonly modelled as rapidly rotating spinning dust grains. The photodissociation region (PDR) at the boundary of the $\lambda$-Orionis H II region has been identified by several recent analyses as one of the brightest spinning dust-emitting sources in the sky. We investigate the Barnard 30 dark cloud, a dark cloud embedded within the $\lambda$-Orionis PDR. We use total-power observations of Barnard 30 from the CO Mapping Array Project (COMAP) pathfinder instrument at 26-34GHz with a resolution of 4.5 arcmin alongside existing data from Planck, WISE, IRAS, ACT, and the 1.447 GHz GALFACTS survey. We use aperture photometry and template fitting to measure the spectral energy distribution of Barnard 30. We find that the spinning dust is the dominant emission component in the 26-34GHz range at the $6\, \sigma$ level ($S_{30\, \mathrm{GHz}} = 3.35\pm 0.56$ Jy). From correlating COMAP data with dust templates we find no evidence that polycyclic aromatic hydrocarbons are the preferred carrier for the spinning dust emission, suggesting that the spinning dust carriers are due to a mixed population of very small grains. Finally, we find evidence for variations in spinning dust emissivity and peak frequency within Barnard 30, and that these variations are possibly driven by changes in dust grain population and the total radiation field. Confirming the origin of the variations in the spinning dust spectrum will require both future COMAP observations at 15 GHz combined with spectroscopic mid-infrared data of Barnard 30.