Recognizing the properties of the host galaxies of quasi-stellar objects ( QSOs ) is essential for understanding the suspected coevolution of central supermassive black holes ( BHs ) and their host galaxies .
Low-luminosity type-1 QSOs ( LLQSOs ) are ideal targets because of their small cosmological distance , which allows a for detailed structural analysis .
We selected a subsample of the Hamburg/ESO survey for bright UV-excess QSOs that contains only the 99 nearest QSOs with redshift z \leq 0.06 .
From this low-luminosity type-1 QSO sample , we observed 20 galaxies and performed aperture photometry and bulge-disk-decomposition with BUDDA on near-infrared J - , H - , and K -band images to separate disk , bulge , bar , and nuclear component .
From the photometric decomposition of these 20 objects and visual inspection of images of another 26 , we find that \sim 50 % of the hosts are disk galaxies and most of them ( 86 % ) are barred .
Stellar masses , calculated from parametric models based on inactive galaxy colors , range from 2 \times 10 ^ { 9 } M _ { \odot } to 2 \times 10 ^ { 11 } M _ { \odot } with an average mass of 7 \times 10 ^ { 10 } M _ { \odot } .
Black hole masses measured from single-epoch spectroscopy range from 1 \times 10 ^ { 6 } M _ { \odot } to 5 \times 10 ^ { 8 } M _ { \odot } with a median mass of 3 \times 10 ^ { 7 } M _ { \odot } .
In comparison with higher-luminosity QSO samples , LLQSOs tend to have lower stellar and BH masses .
Moreover , in the effective radius vs. mean surface-brightness projection of the fundamental plane , they lie in the transition area between luminous QSOs and normal galaxies .
This can be seen as additional evidence that they populate a region intermediate between the local Seyfert population and luminous QSOs at higher redshift .
This region has not been well studied so far .
Eleven low-luminosity type-1 QSOs , for which we have reliable morphological decompositions and BH mass estimations , lie below the published BH mass vs. bulge luminosity relations for inactive galaxies .
This can partially be explained if one assumes that the bulges of active galaxies contain much younger stellar populations than the bulges of inactive galaxies .
Another possibility would be that their BHs are undermassive .
This might indicate that the growth of the host spheroid precedes that of the BH .