A New Calibration of Star Formation Rate in Galaxies Based on Polycyclic Aromatic Hydrocarbon Emission

Abstract

Polycyclic aromatic hydrocarbon (PAH) emission has long been proposed to be a potential star formation rate indicator, as it arises from the photodissociation region bordering the Strömgren sphere of young, massive stars. We apply a recently developed technique of mid-infrared spectral decomposition to obtain a uniform set of PAH measurements from Spitzer  low-resolution spectra of a large sample of star-forming galaxies spanning a wide range in stellar mass ( M ⋆  ≈ 10 6 –10 11.4 M ⊙ ) and star formation rate (∼0.1–2000 M ⊙ yr −1 ). High-resolution spectra are also analyzed to measure [Ne ii ] 12.8 μ m and [Ne iii ] 15.6 μ m, which effectively trace the Lyman continuum. We present a new relation between PAH luminosity and star formation rate based on the [Ne ii ] and [Ne iii ] lines. Calibrations are given for the integrated 5–15 μ m PAH emission, the individual features at 6.2, 7.7, 8.6, and 11.3 μ m, as well as several mid-infrared bandpasses sensitive to PAH. We confirm that PAH emission is suppressed in low-mass dwarf galaxies, and we discuss the possible physical origin of this effect.