AKARI Near-Infrared Spectroscopy of Luminous Infrared Galaxies
  We present the AKARI near-infrared (NIR; 2.5-5 micron) spectroscopic study of
36 (ultra)luminous infrared galaxies [(U)LIRGs] at z=0.01-0.4. We measure the
NIR spectral features including the strengths of 3.3 micron polycyclic aromatic
hydrocarbon (PAH) emission and hydrogen recombination lines (Br\alpha. and
Br\beta), optical depths at 3.1 and 3.4 micron, and NIR continuum slope. These
spectral features are used to identify optically elusive, buried AGN. We find
that half of the (U)LIRGs optically classified as non-Seyferts show AGN
signatures in their NIR spectra. Using a combined sample of (U)LIRGs with NIR
spectra in the literature, we measure the contribution of buried AGN to the
infrared luminosity from the SED-fitting to the IRAS photometry. The
contribution of these buried AGN to the infrared luminosity is 5-10%, smaller
than the typical AGN contribution of (U)LIRGs including Seyfert galaxies
(10-40%). We show that NIR continuum slopes correlate well with WISE
[3.4]-[4.6] colors, which would be useful for identifying a large number of
buried AGN using the WISE data.
