Infrared 3-4 Micron Spectroscopy of Nearby PG QSOs and AGN-Nuclear
  Starburst Connections in High-luminosity AGN Populations
  We present the results of infrared L-band (3-4 micron) slit spectroscopy of
30 PG QSOs at z < 0.17, the representative sample of local high-luminosity,
optically selected AGNs. The 3.3 micron polycyclic aromatic hydrocarbon (PAH)
emission feature is used to probe nuclear (< a few kpc) starburst activity and
to investigate the connections between AGNs and nuclear starbursts in PG QSOs.
The 3.3 micron PAH emission is detected in the individual spectra of 5/30 of
the observed PG QSOs. We construct a composite spectrum of PAH-undetected PG
QSOs and discern the presence of the 3.3 micron PAH emission therein. We
estimate the nuclear-starburst and AGN luminosities from the observed 3.3
micron PAH emission and 3.35 micron continuum luminosities, respectively, and
find that the nuclear-starburst-to-AGN luminosity ratios in PG QSOs are similar
to those of previously studied AGN populations with lower luminosities,
suggesting that AGN-nuclear starburst connections are valid over the wide
luminosity range of AGNs in the local universe. The observed
nuclear-starburst-to-AGN luminosity ratios in PG QSOs with available
supermassive black hole masses are comparable to a theoretical prediction based
on the assumption that the growth of a supermassive black hole is controlled by
starburst-induced turbulence.
