A Principal Component Analysis of polycyclic aromatic hydrocarbon emission in NGC 2023

Abstract

We use the measured fluxes of polycyclic aromatic hydrocarbon (PAH) emission features at 6.2, 7.7, 8.6, 11.0 and 11.2 $\mu$m in the reflection nebula NGC 2023 to carry out a principal component analysis (PCA) as a means to study previously reported variations in the PAH emission. We find that almost all of the variations (99%) can be explained with just two parameters -- the first two principal components (PCs). We explore the characteristics of these PCs and show that the first PC ($P{C}_1$), which is the primary driver of the variation, represents the amount of emission of a mixture of PAHs with ionized species dominating over neutral species. The second PC ($P{C}_2$) traces variations in the ionization state of the PAHs across the nebula. Correlations of the PCs with various PAH ratios show that the 6.2 and 7.7 $\mu$m bands behave differently than the 8.6 and 11.0 $\mu$m bands, thereby forming two distinct groups of ionized bands. We compare the spatial distribution of the PCs to the physical conditions, in particular to the strength of the radiation field, $G_0$, and the $G_0/n_H$ ratio and find that the variations in $P{C}_2$, i.e. the ionization state of PAHs are strongly affected by $G_0$ whereas the amount of PAH emission (as traced by $P{C}_1$) does not depend on $G_0$.

16 pages, 12 figures, accepted for publication in MNRAS

References in corpus (35)

• The Spitzer Space Telescope Mission
• The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
• The Infrared Spectrograph on the Spitzer Space Telescope
• Infrared Emission from Interstellar Dust. II. The Diffuse Interstellar Medium
• The Mid-Infrared Spectrum of Star-Forming Galaxies: Global Properties of PAH Emission
• Structure of Stationary Photodissociation Fronts
• Far Infrared and Submillimeter Emission from Galactic and Extragalactic Photo-Dissociation Regions
• The rich 6 to 9 um spectrum of interstellar PAHs
• Common-Resolution Convolution Kernels for Space- and Ground-Based Telescopes
• The CH out-of-plane bending modes of PAH molecules in astrophysical environments
• Formation of buckminsterfullerene (C60) in interstellar space
• The APOGEE-2 Survey of the Orion Star Forming Complex II: Six-dimensional structure
• Variations of the Mid-IR Aromatic Features Inside and Among Galaxies
• Analysis of the emission of very small dust particles from Spitzer spectro-imagery data using blind signal separation methods
• The infrared spectra of very large, compact, highly symmetric, polycyclic aromatic hydrocarbons (PAHs)
• The aromatic infrared bands as seen by ISO-SWS: probing the PAH model
• The Infrared Spectra of Very Large Irregular Polycyclic Aromatic Hydrocarbons (PAHs): Observational Probes of Astronomical PAH Geometry, Size and Charge
• Evaporating Very Small Grains as tracers of the UV radiation field in Photo-dissociation Regions
• Mapping PAH sizes in NGC 7023 with SOFIA
• The PAH emission characteristics of the reflection nebula NGC2023
• Probing the size and charge of Polycyclic Aromatic Hydrocarbons
• Direct spectroscopic evidence for ionized PAHs in the interstellar medium
• Variations of the Mid-IR Emission Spectrum in Reflection Nebulae
• The 15-20 um emission in the reflection nebula NGC2023
• Spitzer Mapping of PAHs and H2 in Photodissociation Regions
• Coupled Blind Signal Separation and Spectroscopic Database Fitting of the Mid Infrared PAH Features
• PAHs and star formation in the HII regions of nearby galaxies M83 and M33
• PDR Model Mapping of Physical Conditions via Spitzer/IRS Spectroscopy of H2: Theoretical Success toward NGC 2023-South
• Polycyclic Aromatic Hydrocarbons with armchair edges and the 12.7 μm band
• Polycyclic Aromatic Hydrocarbon emission in Spitzer/IRS maps I: Catalog and simple diagnostics
• Polycyclic Aromatic Hydrocarbon emission in Spitzer/IRS maps II: A direct link between band profiles and the radiation field strength
• Interpreting the subtle spectral variations of the 11.2 and 12.7 μm polycyclic aromatic hydrocarbon bands
• The mid-infrared appearance of the Galactic Mini-Starburst W49A
• High Spectral and Spatial Resolution Observations of the PDR Emission in the NGC2023 Reflection Nebula with SOFIA and APEX
• An In-Depth View of the Mid-Infrared Properties of Point Sources and the Diffuse ISM in the SMC Giant HII Region, N66

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