UCLA

Polycyclic aromatic hydrocarbon (PAH) dust emission has been proposed as an effective extinction-independent star formation rate (SFR) indicator in the mid-infrared (MIR), but is sensitive to conditions in the interstellar medium. This thesis is based on MIR photometric data from the AKARI/Infrared Camera (IRC), which provides a representative and unbiased sample for studying the effects of metallicity, starburst intensity, and active galactic nuclei (AGN) on PAH dust emission. Our observations include follow-up, rest-frame optical spectra of 443 galaxies within the AKARI North Ecliptic Pole survey that have IRC detections from 7—24 $\mu$m. We use optical emission line diagnostics to measure gas-phase metallicity, to classify the source of ionizing photons, to measure dust extinction, and to infer star formation rate (SFR) based on H$\alpha$ and [O II]$\lambda\lambda 3726,3729$ emission line luminosities. We show that the PAH 6.2 $\mu$m and PAH 7.7 $\mu$m luminosities ($L(PAH\ 6.2\ \mu m)$ and $L(PAH\ 7.7\ \mu m)$, respectively) derived using multi-wavelength model fits are consistent with those derived from slitless spectroscopy within 0.2 dex. We find that $L(PAH\ 6.2\ \mu m)$ and $L(PAH\ 7.7\ \mu m)$ correlate linearly with the 24 $\mu$m-dust corrected H$\alpha$ luminosity only for normal, main-sequence galaxies. Assuming multi-linear fits, we quantify the additional dependencies on gas-phase metallicity and starburst intensity, which we use to correct our PAH SFR calibrations at $0