The Kinematics of Polycyclic Aromatic Hydrocarbons (PAHs) in Galaxies revealed by Principal Component Analysis (PCA) tomography with JWST/NIRSpec

Fergus R. Donnan, Dimitra Rigopoulou, Ismael García-Bernete

Published 2024-05-22Version 1

Polycyclic Aromatic Hydrocarbons (PAHs) are organic molecules which comprise the smallest particles of dust in the interstellar medium (ISM). Due to their broad/complex emission profiles, obtaining kinematics is a challenge with traditional methods, especially before the advent of the JWST. In this work we employ Principal Component Analysis (PCA) tomography to analyse JWST/NIRSpec IFU data of 3 nearby luminous infrared galaxies (LIRGs), namely, NGC 3256 N, NGC 3256 S and NGC 7469. We detect the signature of rotation in the second principal component of the 3.3 $\mu$m PAH feature in all three targets. We construct velocity maps from the principal components for the 3.3 $\mu$m PAH feature, Br$\beta$ (2.625$\mu$m) and molecular hydrogen, H$_2$ 1-0 S(1) (2.12$\mu$m). We find that in each target, the PAHs qualitatively follow the rotation of the galaxy, consistent with the rotational signature derived from Br$\beta$ and H$_2$. There are however some differences, with the PAH rotation in NGC 3256 N appearing at a different position angle, which suggest differences in the motion of the dust as compared to the gas. This kind of analysis opens a new window into this key component of the ISM.