A low-luminosity type-1 QSO sample V. Overluminous host spheroids and their excitation mechanisms

We present near-infrared (NIR) H + K-band long-slit spectra of eleven galaxies that were obtained with SOFI at the NTT (ESO). The galaxies are chosen from the low-luminosity type-1 quasi-stellar object (LLQSO) sample, which comprises the 99 closest (z <= 0.06) QSOs from the Hamburg/ESO survey for bright UV-excess QSOs. These objects are ideal targets to study the gap between local Seyfert galaxies and high-redshift quasars because they show much stronger AGN activity than local objects, but are still close enough for a detailed structural analysis. We fit hydrogen recombination, molecular hydrogen, and [Fe II] lines after carefully subtracting the continuum emission. From the broad Paa components, we estimated black hole masses and enlarged the sample of LLQSOs that deviate from the M-BH-L-buige relations of inactive galaxies from 12 to 16 objects. All objects show emission from hot dust (T similar to 1200 K) as well as stellar contribution. However, the respective fractions vary strongly among the objects. More than half of the objects show H-2 emission lines, which indicate a large reservoir of molecular gas that is needed to feed the AGN and star formation. In the NIR diagnostic diagram all objects lie in the location of AGN-dominated objects. However, most of the objects show indications of star formation activity, suggesting that their offset location with respect to M-BH-L-buige relations of inactive galaxies may be a consequence of overluminous bulges.