The Calibration of Polycyclic Aromatic Hydrocarbon Dust Emission as a Star Formation Rate Indicator in the AKARI NEP Survey

Abstract

Polycyclic aromatic hydrocarbon (PAH) dust emission has been proposed as an effective extinction-independent star formation rate (SFR) indicator in the mid-infrared, but this may depend on conditions in the interstellar medium. The coverage of the AKARI/Infrared Camera (IRC) allows us to study the effects of metallicity, starburst intensity, and active galactic nuclei on PAH emission in galaxies with f _ν ( L 18 W ) ≲ 19 AB mag. Observations include follow-up, rest-frame optical spectra of 443 galaxies within the AKARI North Ecliptic Pole survey that have IRC detections from 7 to 24 μ m. We use optical emission line diagnostics to infer SFR based on H α and [O ii ] λ λ 3726, 3729 emission line luminosities. The PAH 6.2 μ m and PAH 7.7 μ m luminosities ( L (PAH 6.2 μ m) and L (PAH 7.7 μ m), respectively) derived using multiwavelength model fits are consistent with those derived from slitless spectroscopy within 0.2 dex. L (PAH 6.2 μ m) and L (PAH 7.7 μ m) correlate linearly with the 24 μ m dust-corrected H α luminosity only for normal, star-forming “main-sequence” galaxies. Assuming multilinear correlations, we quantify the additional dependencies on metallicity and starburst intensity, which we use to correct our PAH SFR calibrations at 0 < z < 1.2 for the first time. We derive the cosmic star formation rate density (SFRD) per comoving volume from 0.15 ≲ z ≲ 1. The PAH SFRD is consistent with that of the far-infrared and reaches an order of magnitude higher than that of uncorrected UV observations at z ∼ 1. Starburst galaxies contribute ≳0.7 of the total SFRD at z ∼ 1 compared to main-sequence galaxies.

Keywords

• Star formation
• Polycyclic aromatic hydrocarbons
• Interstellar dust
• Infrared galaxies
• Infrared photometry
• Spectral energy distribution