Excitation and Destruction of Small Polycyclic Aromatic Hydrocarbons by the Luminous Seyfert Nucleus of NGC 4151

We present a spatially-resolved detection of $3.3\,\mathrm{μm}$ emission from polycyclic aromatic hydrocarbons (PAHs) within the circumnuclear ${\sim}200\,\mathrm{pc}$ of the archetypal Seyfert galaxy NGC 4151, using new JWST NIRSpec/IFU spectroscopy. PAHs are detected down to the innermost $50\,\mathrm{pc}$, though it is likely that PAHs also exist at smaller radii, as PAH detections closer than this seem to be limited by continuum dilution. This is contrary to expectations that PAH grains, especially the smallest grains that carry the $3.3\,\mathrm{μm}$ feature, could not survive near an active galactic nucleus (AGN). Furthermore, the surface brightness of PAH emission increases as radius from the nucleus decreases. We interpret this as evidence that the AGN supplies energy for PAH excitation by driving ultraviolet emission in nearby H and $\mathrm{H_2}$ gas. We do not detect PAH emission within the narrow line region (NLR) that hosts highly ionized and outflowing gas, suggesting that the AGN may also destroy PAHs in these regions, depending on geometry. Together, these results show that an AGN has a complex, multifaceted role in the life cycle of PAHs and in PAH excitation.