We have obtained high resolution images of the central regions of 14 reverberation-mapped active galactic nuclei ( AGN ) using the Hubble Space Telescope Advanced Camera for Surveys High Resolution Camera to account for host-galaxy starlight contamination of measured AGN luminosities .
We measure the host-galaxy starlight contribution to the continuum luminosity at 5100 Å through the typical ground-based slit position and geometry used in the reverberation-mapping campaigns .
We find that removing the starlight contribution results in a significant correction to the luminosity of each AGN , both for lower luminosity sources , as expected , but also for the higher luminosity sources such as the PG quasars .
After accounting for the host galaxy starlight , we revisit the well-known broad-line region radius–luminosity relationship for nearby AGN .
We find the power-law slope of the relationship for the H \beta line to be 0.518 \pm 0.039 , shallower than previously reported and consistent with the slope of 0.5 expected from the naive theoretical assumption that all AGN have , on average , the same ionizing spectrum and the same ionization parameter and gas density in the H \beta line-emitting region .