Spatial analysis of PAH molecules in the Pillars of Creation using JWST

Abstract

I present a spatially resolved analysis of the polycyclic aromatic hydrocarbon (PAH) population in the Pillars of Creation within the Eagle Nebula (M16) using the James Webb Space Telescope's (JWST) Mid Infrared Instrument (MIRI) and Near Infrared Camera (NIRCam) imaging. By using mid infrared PAH sensitive bands, I derive resolved maps of PAH size and ionization state across the pillars and connect these directly to variations in the radiation field and gas structure. I present the first spatial maps of PAH ionization and size in the Pillars of Creation. The analysis reveals clear internal gradients that show the PAH population is strongly shaped by local conditions within the cloud, such as the local radiation intensity and orientation of the nebular structure. The intensely radiated regions show a neutral and large PAH population, possibly due to electron recombination in these regions. I measure a mean PAH size of 198 carbon atoms with an error bar of 1.22 for M16 and use the resolved emission structure to obtain a first-order estimate of the electron density in the molecular cloud. These results provide direct evidence that PAH properties in M16 are governed by the interplay between radiation and density on sub-cloud scales, demonstrating the power of JWST imaging to probe dust processing in star-forming regions.

Figures (8)

• Figure 1: Image depicting the stellar removal process. Left panel image shows the original F335M image with the different regions of the nebula written in red. The right panel shows the image after the star removal process. We can see that most of the bright stars have removed and the gas cloud is better highlighted.
• Figure 2: F187N image showing Pa$\alpha$ emission line flux (MJy/sr), which can be treated as a proxy for FUV radiation. The dark blue regions have flux of the order $10^0$ MJy/sr, and the bright yellow regions have flux of the order $10^2$ MJy/sr. The image shows the stellar radiation which is coming from the NGC6611 cluster located above the pillars. North is up and east is to the left.
• Figure 3: RGB composite of the Pillars of Creation in the Eagle Nebula (M16) observed with JWST. Blue corresponds to Filter NIRCAM F187N which shows the FUV radiation, red to NIRCAM F470N tracing the molecular gas, and green to the MIRI F770W which traces the 7.7$\mu$m PAH feature. The image highlights spatial variations in PAH emission along the irradiated surfaces of the pillars, with enhanced PAH intensity at the ionization fronts facing the central OB cluster. North is up and east is to the left.
• Figure 4: Spatial Map showing the distribution of different ionization states in the nebula. Yellow corresponds to neutral states which populate Pillar 1, and skins of Pillar 2. While blue regions represent cationic ionization states, which are located deeper in the nebula, far away from the intense steallr radiation.
• Figure 5: Spatial map showing the size of PAH molecules in different regions of the nebula. The number of carbon atoms represent the size of the PAH molecule. The map shows distinct gradients in the size, with Pillar 1 showing molecules with $N_c$ (Number of carbon atoms) > 300, while the molecular cloud having molecules with $N_c \sim 200$.