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 Physics , 1998, DOI: 10.1046/j.1365-8711.1999.02676.x Abstract: We present the first results from a major HST WFPC2 imaging study aimed at providing the first statistically meaningful comparison of the morphologies, luminosities, scalelengths and colours of the host galaxies of radio-quiet quasars, radio-loud quasars, and radio galaxies. We describe the design of this study and present the images which have been obtained for the first half of our 33-source sample. We find that the hosts of all three classes of luminous AGN are massive elliptical galaxies, with scalelengths ~=10 kpc, and R-K colours consistent with mature stellar populations. Most importantly this is the the first unambiguous evidence that, just like radio-loud quasars, essentially all radio-quiet quasars brighter than M_R = -24 reside in massive ellipticals. This result removes the possibility that radio loudness' is directly linked to host galaxy morphology, but is however in excellent accord with the black-hole/spheroid mass correlation recently highlighted by Magorrian et al. (1998). We apply the relations given by Magorrian et al. to infer the expected Eddington luminosity of the putative black hole at the centre of each of the spheroidal host galaxies we have uncovered. Comparison with the actual nuclear R-band luminosities suggests that the black holes in most of these galaxies are radiating at a few percent of the Eddington luminosity; the brightest host galaxies in our low-z sample are capable of hosting quasars with M_R = -28, comparable to the most luminous quasars at z = 3. Finally we discuss our host-derived black-hole masses in the context of the radio-luminosity:black-hole mass correlation recently uncovered for nearby galaxies by Franceschini et al. (1998), and the resulting implications for the physical origin of radio loudness.
 Physics , 2001, Abstract: We compare the host galaxies properties of BL Lac objects with those of radio loud quasars (RLQs) imaged by the WFPC2 on board of HST. The considered objects (z<0.5) are always well resolved and their host galaxies satisfactorily modelled by ellipticals. After homogeneous treatment of the data we find RLQs hosts are systematically more luminous (by ~0.7 mag) with respect to the hosts of BL Lacs. Using the M_BH - L_bulge relation, derived for nearby elliptical galaxies, we have evaluated the central black hole masses of our sample of active galaxies. These data are discussed in conjunction with the nuclear luminosity and the Eddington ratio.
 Physics , 2000, Abstract: We have observed a complete sample of 21 nearby (D < 70h^{-1} Mpc) Fanaroff & Riley Type I galaxies with HST/WFPC2 and detected dust disks and lanes in 19 of them. The radio jets are roughly perpendicular to the dust which is used to constrain the Doppler boosting factors of the radio jet and cores. The VLBA core flux correlates with the central Halpha+[NII] flux which might indicate that the VLBA core is dominated by an isotropic component. Twelve galaxies show nuclear optical sources. We discuss various possible origins for this emission.
 Physics , 2003, DOI: 10.1046/j.1365-8711.2003.06690.x Abstract: We investigate the host galaxy luminosities of BL Lac Objects (BLLs) and Radio Loud Quasars (RLQs) at z<0.5 imaged with the Hubble Space Telescope (HST). From a homogeneous treatment of the data we construct the host galaxy luminosity functions (HGLFs) and find that RLQ hosts are ~0.5 mag brighter than those of BLL: _BLL= -23.5. For both classes the HGLFs exhibit a remarkably different distribution with respect to that of normal (inactive) ellipticals, with clear preference for more luminous galaxies to show nuclear activity. We make use of the black hole mass -- bulge luminosity (M[BH] -L[bulge]) relation, derived for nearby inactive ellipticals, to estimate the central black hole mass in our sample of radio loud active galaxies. In spite of a ~2 order of magnitude difference of intrinsic nuclear luminosity BLL and RLQ have BH of similar mass _BLL= 5.6x10^{8},
 Physics , 2011, DOI: 10.1111/j.1365-2966.2011.18845.x Abstract: Recent results indicate a correlation between nuclear radio-loudness of active galaxies and their central stellar surface-brightness profiles, in that core' galaxies (with inner logarithmic slope {\gamma}<0.3) are significantly more radio loud than power-law' galaxies ({\gamma}>0.5). This connection, which indicates possible links between radio-loudness and galaxy formation history (e.g. through black hole spin) has so far only been confirmed for a radio-selected sample of galaxies. Furthermore, it has since been shown that the Nuker law, which was used to parameterise the brightness profiles in these studies, gives a poor description of the brightness profile. Here, we present an analysis of the central surface brightness profiles of the active galaxies of Hubble Type T<3, that were identified by the optically-selected Palomar spectroscopic survey of nearby galaxies. We fit the brightness profiles using Sersic, Core-Sersic and, where necessary, Double-Sersic models, which we fit to the semi-major axis brightness profiles extracted from high resolution images of the galaxies from the Hubble Space Telescope (HST). We use these fits to classify the galaxies as Core', Sersic' or Double-Sersic' and compare this classification with the properties of the Active Galactic Nuclei (AGNs). We find that AGN hosted in Core galaxies are generally more radio-loud than those hosted in Sersic galaxies, although there is a large overlap between the two subsamples. The correlation between radio-loudness and brightness profile can partly be explained by a correlation between radio-loudness and black hole mass. Additionally, there is a significant (99 per cent confidence) partial correlation between radio-loudness and the Core/Sersic classification of the host galaxy, which lends support to the previous results based on the radio-selected sample.