Characterizing Spatial Variations of PAH Emission in the Reflection Nebula NGC 1333

• Main Authors: Knight, C, Peeters, E, Wolfire, M, Stock, D. J
• Format: Journal Article
• Language: English
• Published: 15-11-2021
• Subjects: Physics - Astrophysics of Galaxies
• DOI: 10.48550/arxiv.2111.08139

Infrared emission features at 3.3, 6.2, 7.7, 8.6, and 11.2 $\mu$m, attributed
to polycyclic aromatic hydrocarbons, show variations in relative intensity,
shape, and peak position. These variations depend on the physical conditions of
the photodissociation region (PDR) in which strong PAH emission arises, but
their relationship has yet to be fully quantified. We aim to better calibrate
the response of PAH species to their environment using observations with
matching apertures and spatial resolution. We present observations from the
Field-Imaging Far-Infrared Line Spectrometer (FIFI-LS) on board the
Stratospheric Observatory for Infrared Astronomy (SOFIA) of the gas cooling
lines [OI] 63, 146 $\mu$m and [CII] 158 $\mu$m in the reflection nebula NGC
1333 and use archival dust continuum observations from the Photodetector Array
Camera and Spectrometer (PACS) on board Herschel. We employ PDR modelling to
derive the physical conditions and compare these with the characteristics of
the PAH emission as observed with the Infrared Spectrometer (IRS) on board
Spitzer. We find distinct spatial characteristics for the various PAH spectral
components. We conclude that the ionic bands (6.2, 7.7, 8.6, and 11.0) and the
7-9 $\mu$m emission are due to multiple PAH sub-populations and that the
plateaus are distinct from the features perched on top. The 6-9 $\mu$m PAH
emission exhibit a significant change in behaviour between the irradiated PDR
and diffuse outskirts, confirming these bands arise from multiple PAH
sub-populations with different underlying molecular properties. We find
multiple promising relationships between PAH ratios and the FUV radiation field
strength but no clear correlations with the PAH ionization parameter.