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A comparative HST imaging study of the host galaxies of radio-quiet quasars, radio-loud quasars and radio galaxies: Paper I  [PDF]
R. J. McLure,J. S. Dunlop,M. J. Kukula,S. A. Baum,C. P. O'Dea,D. H. Hughes
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.
Host galaxies, BH masses and Eddington ratio of radio-loud AGNs  [PDF]
A. Treves,N. Carangelo,R. Falomo,C. M. Urry,M. O'Dowd,R. Scarpa
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.
The Nuclei of Nearby Radio-Loud Ellipticals  [PDF]
G. A. Verdoes Kleijn,P. T. de Zeeuw,S. A. Baum,C. P. O'Dea,R. P. van der Marel,C. Xu,C. M. Carollo,J. Noel-Storr
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.
Host galaxies and black hole masses of low and high luminosity radio loud active nuclei  [PDF]
Renato Falomo,Nicoletta Carangelo,Aldo Treves
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},
The connection between radio-loudness and central surface brightness profiles in optically-selected low-luminosity active galaxies  [PDF]
A. J. Richings,P. Uttley,E. Kording
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.
Compact Radio Cores in the Galactic Center and Elsewhere  [PDF]
Heino Falcke
Physics , 1996,
Abstract: Compact radio cores are not only common in radio galaxies and quasars but also in many nearby galaxies with low-active, supermassive black holes. One famous example is the Galactic Center source Sgr A*. Recent studies of proper motions and radial velocities of stars in the inner parsec of the Galaxy convincingly demonstrate the presence of a compact dark mass of 2.5 10^6 Mo in the nucleus of the Milky Way. Millimeter VLBI and submm observations of Sgr A* thus probe a region of only a few Schwarzschild radii in diameter. In this paper I will review our current theoretical and observational knowledge of this source and compare it to some famous LINER galaxies like NGC 4258, NGC 3079, and NGC 6500. In all cases these radio cores can be well explained by a standard AGN jet model, and, with the exception of Sgr A*, large scale outflows are observed that have powers comparable to those inferred from the radio cores. Recent VLBI observations of radio-weak quasars and HST observations of Seyfert galaxies indicate that these AGN also produce powerful jets which, however, have relatively less luminous radio cores than radio-loud quasars and the LINERs discussed here. Therefore, jets and compact radio cores appear to be natural constituents of an AGN, but the reason why apparently some jets are radio-loud and others not remains a mystery.
Millimeter observations of radio-loud active galaxies  [PDF]
Ilse van Bemmel,Frank Bertoldi
Physics , 2001, DOI: 10.1051/0004-6361:20010040
Abstract: In order to study the nature of the far-infrared emission observed in radio-loud active galaxies, we have obtained 1.2 mm observations with the IRAM 30 m telescope for a sample of eight radio-loud active galaxies. In all objects we find that the 1.2 mm emission is dominated by non-thermal emission. An extrapolation of the non-thermal radio spectrum indicates that the contribution of synchrotron emission to the far-infrared is less than 10% in quasars, and negligible in the radio galaxies. The quasars in the sample show signs of relativistic beaming at millimeter wavelengths, and the quasar 3C334 shows evidence for strong variability.
Examining the Radio-Loud/Radio-Quiet dichotomy with new Chandra and VLA observations of 13 UGC galaxies  [PDF]
Preeti Kharb,A. Capetti,D. J. Axon,M. Chiaberge,P. Grandi,A. Robinson,G. Giovannini,B. Balmaverde,D. Macchetto,R. Montez
Physics , 2012, DOI: 10.1088/0004-6256/143/4/78
Abstract: (Abridged) We present the results from new 15 ks Chandra-ACIS and 4.9 GHz Very Large Array observations of 13 galaxies hosting low luminosity AGN. This completes the multiwavelength study of a sample of 51 nearby early-type galaxies described in Capetti & Balmaverde (2005, 2006); Balmaverde & Capetti (2006). The aim of the three previous papers was to explore the connection between the host galaxies and AGN activity in a radio-selected sample. We detect nuclear X-ray emission in eight sources and radio emission in all but one (viz., UGC6985). The new VLA observations improve the spatial resolution by a factor of ten: the presence of nuclear radio sources in 12 of the 13 galaxies confirms their AGN nature. As previously indicated, the behavior of the X-ray and radio emission in these sources depends strongly on the form of their optical surface brightness profiles derived from Hubble Space Telescope imaging, i.e., on their classification as "core", "power-law" or "intermediate" galaxies. With more than twice the number of "power-law" and "intermediate" galaxies compared to previous work, we confirm with a much higher statistical significance that these galaxies lie well above the radio-X-ray correlation established in FRI radio galaxies and the low-luminosity "core" galaxies. This result highlights the fact that the "radio-loud/radio-quiet" dichotomy is a function of the host galaxy's optical surface brightness profile. We present radio-optical-X-ray spectral indices for all 51 sample galaxies. Survival statistics point to significant differences in the radio-to-optical and radio-to-X-ray spectral indices between the "core" and "power-law" galaxies (Gehan's Generalized Wilcoxon test probability "p" for the two classes being statistically similar is <10^-5), but not in the optical-to-X-ray spectral indices (p=0.25).
Nearby radio loud AGN and the Unified Model  [PDF]
Elisabetta Liuzzo,Gabriele Giovannini,Marcello Giroletti
Physics , 2015,
Abstract: The statistical study of the parsec scale properties of radio sources is crucial to get information on the nature of the central engine and to provide the foundations of the current unified theories, suggesting that the appearance of active galactic nuclei depends strongly on orientation. We started a project to observe at sub-arcsec resolution a complete sample of 94 nearby (z<0.1) radio galaxies, the Bologna Complete Sample, which is not affected by any selection effect on the jet velocity and orientation with respect to the line of sight. Up to now, we published our parsec scale analysis of 77/94 sources. Here, we describe the last VLBA observations at 5 GHz and EVN data at 18 cm obtained for the 17 remaining faintest radio core (<5 mJy at 5 GHz in VLA images) BCS sources and we report our preliminary results on the whole complete sample.
Host Galaxies of low z Radio-loud Quasars: A search of HST archives  [PDF]
C. Pagani,R. Falomo,A. Treves
Physics , 2003, DOI: 10.1086/378199
Abstract: We searched the HST archives for unpublished WFPC2 images of low redshift (z<0.5) radio loud quasars (RLQ). This led to the identification of 11 objects. We present here 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 which significantly expands all previous studies of low redshift RLQ based on HST data. For this full sample we derive the average absolute magnitude of the host galaxies =-24.01+/-0.48, and the effective radius =10.5+/-3.7kpc. 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 M_BH and total radio power for RLQ and compare with other classes of radio sources. The overall distribution of AGN in the plane M_BH-P(radio) exhibits a trend for increasing M_BH with increasing P(radio) but with a substantial spread. RLQ occupy the region of most powerful sources and most massive BH. The quasars appear to emit over a wide range of power with respect to their Eddington luminosity as deduced by the estimated M_BH.
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