SPHEREx: Aromatics, Aliphatics, and PAH Size across the Iris Nebula

Abstract Observations by the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) are combined with counterpart Spitzer spectral map data to study the aromatic, aliphatic, and polycyclic aromatic hydrocarbon (PAH) size evolution across the northwest photodissociation region (PDR) of the Iris Nebula (NGC 7023). The 3.3–3.4 μ m complex (I 3.3 ) and 11.2 μ m (I 11.2 ) PAH band strength are determined through direct integration. In addition, the former is decomposed into a 3.3 ( I ′ 3.3 ) and 3.4 μ m ( I ′ 3.4 ) subfeature by fitting SPHEREx bandpass-integrated photometry using a modeled, highly sampled, multicomponent spectrum. I 3.3 , I 11.2 , I ′ 3.3 , and I ′ 3.4 all peak at the PDR. The NASA Ames PAH IR Spectroscopic Database is used to obtain the average number of carbon atoms ( N C ¯ ) and small PAH fraction ( f small ) by fitting the isolated PAH component of the Spitzer segment: 70 ≲ N C ¯ ≲ 76 and 0.24 ≲ f small ≲ 0.36, respectively. I ′ 3.4 / I ′ 3.3 , I 11.2 /I 3.3 , N C ¯ , and f small all show a demarcation that matches the large-scale morphology of the region. For I ′ 3.3 and