AKARI Near-Infrared Spectroscopy of SDSS-Selected Blue Early-Type
  Galaxies
  A near-infrared (NIR; 2.5 - 4.5 micron) spectroscopic survey of SDSS(Sloan
Digital Sky Survey)-selected blue early-type galaxies (BEGs) has been conducted
using the AKARI. The NIR spectra of 36 BEGs are secured, which are well
balanced in their star-formation(SF)/Seyfert/LINER type composition. For high
signal-to-noise ratio, we stack the BEG spectra all and in bins of several
properties: color, specific star formation rate and optically-determined
spectral type. We estimate the NIR continuum slope and the equivalent width of
3.29 micron PAH emission. In the comparison between the estimated NIR spectral
features of the BEGs and those of model galaxies, the BEGs seem to be
old-SSP(Simple Stellar Population)-dominated metal-rich galaxies with moderate
dust attenuation. The dust attenuation in the BEGs may originate from recent
star formation or AGN activity and the BEGs have a clear feature of PAH
emission, the evidence of current SF. BEGs show NIR features different from
those of ULIRGs, from which we do not find any clear relationship between BEGs
and ULIRGs. We find that Seyfert BEGs have more active SF than LINER BEGs, in
spite of the fact that Seyferts show stronger AGN activity than LINERs. One
possible scenario satisfying both our results and the AGN feedback is that SF,
Seyfert and LINER BEGs form an evolutionary sequence: SF - Seyfert - LINER.
