Tracing PAH Emission in $\lambda$-Orionis Using COBE/DIRBE Data

TL;DR

This study maps PAH emission in the $\

Contribution

It introduces a new method to estimate PAH emission using COBE/DIRBE data and investigates its correlation with anomalous microwave emission in $\

Findings

Higher correlation between AME and far-infrared dust emission than with PAH emission.

PAH emission does not strongly correlate with AME, challenging the spinning PAH hypothesis.

Environmental factors may influence the correlation between PAHs and microwave emission.

Abstract

We use archival COBE/DIRBE data to construct a map of polycyclic aromatic hydrocarbon (PAH) emission in the $\lambda$-Orionis region. The presence of the 3.3 $\mu$m PAH feature within the DIRBE 3.5 $\mu$m band and the corresponding lack of significant PAH spectral features in the adjacent DIRBE bands (1.25, 2.2, and 4.9 $\mu$m) enable estimation of the PAH contribution to the 3.5 $\mu$m data. Having the shortest wavelength of known PAH features, the 3.3 $\mu$m feature probes the smallest PAHs, which are also the leading candidates for carriers of anomalous microwave emission (AME). We use this map to investigate the association between the AME and the emission from PAH molecules. We find that the spatial correlation in $\lambda$-Orionis is higher between AME and far-infrared dust emission (as represented by the DIRBE 240 $\mu$m map) than it is between our PAH map and AME. This finding, in agreement with previous studies using PAH features at longer wavelengths, is in tension with the hypothesis that AME is due to spinning PAHs. However, the expected correlation between mid-infrared and microwave emission could potentially be degraded by different sensitivities of each emission mechanism to local environmental conditions even if PAHs are the carriers of both.