The AKARI 2.5-5.0 Micron Spectral Atlas of Type-1 Active Galactic
  Nuclei: Black Hole Mass Estimator, Line Ratio, and Hot Dust Temperature
  We present 2.5-5.0 $\mu$m spectra of 83 nearby ($0.002\,<\,z\,<\,0.48$) and
bright ($K<14$mag) type-1 active galactic nuclei (AGNs) taken with the Infrared
Camera (IRC) on board $\it{AKARI}$. The 2.5-5.0 $\mu$m spectral region contains
emission lines such as Br$\beta$ (2.63 $\mu$m), Br$\alpha$ (4.05 $\mu$m), and
polycyclic aromatic hydrocarbons (PAH; 3.3 $\mu$m), which can be used for
studying the black hole (BH) masses and star formation activities in the host
galaxies of AGNs. The spectral region also suffers less dust extinction than in
the ultra violet (UV) or optical wavelengths, which may provide an unobscured
view of dusty AGNs. Our sample is selected from bright quasar surveys of
Palomar-Green (PG) and SNUQSO, and AGNs with reverberation-mapped BH masses
from Peterson et al. (2004). Using 11 AGNs with reliable detection of Brackett
lines, we derive the Brackett-line-based BH mass estimators. We also find that
the observed Brackett line ratios can be explained with the commonly adopted
physical conditions of the broad line region (BLR). Moreover, we fit the hot
and warm dust components of the dust torus by adding photometric data of SDSS,
2MASS, $\it{WISE}$, and $\it{ISO}$ to the $\it{AKARI}$ spectra, finding hot and
warm dust temperatures of $\sim1100\,\rm{K}$ and $\sim220\,\rm{K}$,
respectively, rather than the commonly cited hot dust temperature of 1500 K.
