Comparison of AGN and Nuclear Starburst Activity in Seyfert 1 and 2
  Galaxies over a Wide Luminosity Range Based on Near-infrared 2-4 micrometer
  Spectroscopy
  We present near-infrared K- (1.9-2.5 micrometer) and L- (2.8-4.2 micrometer)
band spectroscopy of 22 Seyfert nuclei. We use two methods to investigate the
presence of nuclear starbursts: (1) the Polycyclic Aromatic Hydrocarbon (PAH)
emission feature at lambda_rest = 3.3 micrometer in the rest frame of L-band
spectrum (a starburst indicator) and (2) the CO absorption feature at
lambda_rest = 2.3-2.4 micrometer in the rest frame of the K-band spectrum,
originating in the CO molecule. We clearly detected the 3.3 micrometer PAH
emission features in five objects and the CO absorption features in 17 objects.
Seyfert 2 galaxies tend to show bluer K-L colors compared with Seyfert 1
galaxies. We interpret the discrepancy as resulting from relative strength of
stellar emission because AGN emission is affected by dust extinction. The 3.3
micrometer PAH emission luminosity (L_3.3PAH) distributions for the Seyfert 1s
and Seyfert 2s are very similar when normalized to the AGN power.
Star-formation rates estimated from L_3.3PAH could be large enough to inflate
the dusty torus by supernova explosion. We find that L_3.3PAH positively
correlates with N-band luminosity with small aperture over a wide AGN
luminosity range, and is independent of physical area we probed. The results
suggest that nuclear region has a concentration of star formation and the star
formation would control AGN activity.
