Host galaxies of low-z radio-loud quasars:: A search of Hubble Space Telescope archives

We searched the Hubble Space Telescope (HST) archives for unpublished Wide Field Planetary Camera 2 images of low-redshift (z < 0.5) radio-loud quasars (RLQs). This led to the identification of 11 objects. Here we present the results of the analysis of these images from which we derive the properties of their host galaxies. All objects are clearly resolved, and their surrounding nebulosity is consistent with an elliptical galaxy model. These new data, together with previous published HST observations, form a sample of 34 sources that significantly expand all previous studies of low-redshift RLQs based on HST data. For this full sample we derive the average absolute magnitude of the host galaxies [M-R] = - 24.01 +/- 0.48 and the effective radius [R-e] = 10.5 +/- 3.7 kpc. No significant correlation is found between the nucleus and the host galaxy luminosity. Using the relationship between black hole mass (M-BH) and bulge luminosity we investigate the relation between MBH and total radio power for RLQs and compare it with other classes of radio sources. The overall distribution of active galactic nuclei in the M-BH-P-radio plane exhibits a trend for increasing M-BH with increasing P-radio but with a substantial spread. RLQs occupy the region of the most powerful sources and the most massive black hole. The quasars appear to emit over a wide range of power with respect to their Eddington luminosity, as deduced by the estimated M-BH.