All the PAHs: an AKARI-Spitzer Cross Archival Spectroscopic Survey of
  Aromatic Emission in Galaxies
  We present a large sample of 2.5-38 $\mu m$ galaxy spectra drawn from a
cross-archival comparison in the AKARI-Spitzer Extragalactic Spectral Survey
(ASESS), and investigate a subset of 113 star-forming galaxies with prominent
polycyclic aromatic hydrocarbon (PAH) emission spanning a wide range of star
formation properties. With AKARI's extended 2.5-5 $\mu m$ wavelength coverage,
we self-consistently model for the first time all PAH emission bands using a
modified version of PAHFIT. We find $L_\mathrm{PAH\,3.3}/L_\mathrm{IR}$ $\sim$
0.1% and the 3.3 $\mu m$ PAH feature contributes $\sim$1.5-3% to the total PAH
power -- somewhat less than earlier dust models have assumed. We establish a
calibration between 3.3 $\mu m$ PAH emission and star formation rate, but also
find regimes where it loses reliability, including at high luminosity and low
metallicity. The 3.4 $\mu m$ aliphatic emission and a broad plateau feature
centered at 3.47 $\mu m$ are also modeled. As the shortest wavelength PAH
feature, 3.3 $\mu m$ is susceptible to attenuation, leading to a factor of
$\sim$ 3 differences in the inferred star formation rate at high obscuration
with different assumed attenuation geometries. Surprisingly, $L_\mathrm{PAH\,
3.3} / L_\mathrm{\Sigma\, PAH}$ shows no sign of decline at high luminosities,
and the low metallicity dwarf galaxy II Zw 40 exhibits an unusually strong 3.3
$\mu m$ band; both results suggest either that the smallest PAHs are better
able to survive under intense radiation fields than presumed, or that PAH
emission is shifted to shorter wavelengths in intense and high energy radiation
environments. A photometric surrogate for 3.3 $\mu m$ PAH luminosity using
JWST/NIRCam is provided and found to be highly reliable at low redshift.
