The Nucleus-Host Galaxy Connection in Radio-Loud AGN

Abstract

We studied a moderate-redshift (0.15 < z < 0.5) sample of H ST ¹- imaged radio-loud (RL) AGN spanning a large range of nuclear power. The total sample consists of 57 objects, divided into sub-samples of 40 BL Lac objects and 17 RL quasars. Essentially all the AGN nuclei lie in luminous elliptical galaxies (Es), which follow the Kormendy relation for normal Es. The host galaxies occupy a narrow range of ~1 magnitude, compared to >5 orders of magnitude in nuclear power, and the two sub-samples have indistinguishable luminosity-redshift distributions over the redshift range 0.15 < z < 0.5. No correlation between nuclear brightness (corrected for beaming) and galaxy luminosity is seen. Assuming the host galaxy-black hole mass correlation for local galaxies, the derived Eddington ratios range from 2×10^-4 for low-power AGN (BL Lac objects) to 2×10^-1 for high power AGN (RL quasars). This implies a considerable difference in rate of fueling. At least for RL AGN, the host galaxy properties appear to have no close connection to the power of the jet.

Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract No. NAS5-26555.