COMAP Galactic Science I: Observations of Spinning Dust Emission at 30 GHz in Dark Clouds Surrounding the 𝜆-Orionis HII Region

Anomalous Microwave Emission (AME) is a major component of Galactic emission in the frequency band 10\textendash60 GHz that remains poorly understood. AME has been found to have a strong spatial correlation with the dust column along a line-of-sight, and the favored model of AME ascribes the source to rapidly rotating spinning dust grains. The photodissociation region (PDR) at the boundary of the $\lambda$-Orionis H\textsc{ii} region has recently become a target of interest, with multiple results highlighting the ring as one of the brightest spinning dust emitting sources in the sky. We investigate the Barnard~30 dark cloud, which is a sub-region of the $\lambda$-Orionis PDR that was identified by both \textit{Planck}, and more recent combined analyses from \mbox{C-BASS} and QUIJOTE, as the brightest spinning dust emitting region in the PDR. We use new, dedicated total power observations of Barnard~30 from the CO Mapping Array Project (COMAP) pathfinder instrument at 26--34\,GHz with a resolution of $4.\!^\prime5$ alongside existing data from \textit{Planck}, WISE, IRAS, and the 1.447\,GHz GALFACTS survey. We use a combination of aperture photometry and template fitting to measure the spectral energy distribution of Barnard~30, and sub-regions within Barnard~30, and use Markov Chain Monte Carlo modeling to characterize the spectrum in terms of spinning dust and other emission components. We find that the spinning dust is constrained at the $7\,\sigma$ level ($S_{30\mathrm{GHz}} = 2.85\pm0.43$\,Jy) and is the dominant emission component in the COMAP pathfinder band. The spinning dust emission is found to be most strongly correlated with far infrared IRAS data. We find no evidence that polycyclic aromatic hydrocarbons are the preferred carrier for the spinning dust emission, but propose that spinning dust in Barnard~30 is generated by 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 driven by a combination of changes in dust column density and the total radiation field. However, 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.