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Neutral hydrogen in radio galaxies: Results from nearby, importance for far away
The study of neutral hydrogen emission and absorption in radio galaxiesis giving new and important insights on a variety of phenomena observedin these objects. Such observations are helping to understand the originof the host galaxy, the effects of the interaction between the radio jetand the ISM, the presence of fast gaseous outflows as well asjet-induced star formation. Recent results obtained on these phenomenaare summarized in this review. Although the {H I observationsconcentrate on nearby radio galaxies, the results also have relevancefor the high-z objects as all these phenomena are important, and likelyeven more common, in high-redshift radio sources.
| On the X-ray, optical emission line and black hole mass properties of local Seyfert galaxies
We investigate the relation between X-ray nuclear emission, opticalemission line luminosities and black hole masses for a sample of 47Seyfert galaxies. The sample, which has been selected from the Palomaroptical spectroscopic survey of nearby galaxies (Ho et al. 1997a, ApJS,112, 315), covers a wide range of nuclear powers, from L2-10keV ~ 1043 erg/s down to very low luminosities(L2-10 keV ~ 1038 erg/s). Best available data fromChandra, XMM-Newton and, in a few cases, ASCA observations have beenconsidered. Thanks to the good spatial resolution available from theseobservations and a proper modeling of the various spectral components,it has been possible to obtain accurate nuclear X-ray luminosities notcontaminated by off-nuclear sources and/or diffuse emission. X-rayluminosities have then been corrected taking into account the likelycandidate Compton thick sources, which are a high fraction (>30%)among type 2 Seyferts in our sample. The main result of this study isthat we confirm strong linear correlations between 2-10 keV,[OIII]λ5007, Hα luminosities which show the same slope asquasars and luminous Seyfert galaxies, independent of the level ofnuclear activity displayed. Moreover, despite the wide range ofEddington ratios (L/L_Edd) tested here (six orders of magnitude, from0.1 down to ~10-7), no correlation is found between the X-rayor optical emission line luminosities and the black hole mass. Ourresults suggest that Seyfert nuclei in our sample are consistent withbeing a scaled-down version of more luminous AGN.
| The Bologna Complete Sample of Nearby Radio Sources
We present a new, complete sample of 95 radio sources selected from theB2 Catolog of Radio Sources and the Third Cambridge Revised Catalog(3CR), with z<0.1. Since no selection effect on the core radio power,jet velocity, or source orientation is present, this sample is wellsuited for statistical studies. In this first paper we present theobservational status of all sources on the parsec (milliarcsecond) andkiloparsec (arcsecond) scale; we give new parsec-scale data for 28sources and discuss their parsec-scale properties. By combining thesedata with those in the literature, information on the parsec-scalemorphology is available for a total of 53 radio sources with differentradio power and kiloparsec-scale morphologies. We investigate theirproperties. We find a dramatically higher fraction of two-sided sourcesin comparison with that of previous flux-limited VLBI surveys.
| The Westerbork HI survey of spiral and irregular galaxies. III. HI observations of early-type disk galaxies
We present Hi observations of 68 early-type disk galaxies from the WHISPsurvey. They have morphological types between S0 and Sab and absoluteB-band magnitudes between -14 and -22. These galaxies form the massive,high surface-brightness extreme of the disk galaxy population, few ofwhich have been imaged in Hi before. The Hi properties of the galaxiesin our sample span a large range; the average values of MHI/LB and DH I/D25 are comparableto the ones found in later-type spirals, but the dispersions around themean are larger. No significant differences are found between the S0/S0aand the Sa/Sab galaxies. Our early-type disk galaxies follow the same Himass-diameter relation as later-type spiral galaxies, but theireffective Hi surface densities are slightly lower than those found inlater-type systems. In some galaxies, distinct rings of Hi emissioncoincide with regions of enhanced star formation, even though theaverage gas densities are far below the threshold of star formationderived by Kennicutt (1989, ApJ, 344, 685). Apparently, additionalmechanisms, as yet unknown, regulate star formation at low surfacedensities. Many of the galaxies in our sample have lopsided gasmorphologies; in most cases this can be linked to recent or ongoinginteractions or merger events. Asymmetries are rare in quiescentgalaxies. Kinematic lopsidedness is rare, both in interacting andisolated systems. In the appendix, we present an atlas of the Hiobservations: for all galaxies we show Hi surface density maps, globalprofiles, velocity fields and radial surface density profiles.
| Low power compact radio galaxies at high angular resolution
We present sub-arcsecond resolution multi-frequency (8 and 22 GHz) VLAimages of five low power compact (LPC) radio sources, and phasereferenced VLBA images at 1.6 GHz of their nuclear regions. At the VLAresolution we resolve the structure and identify component positions andflux densities. The phase referenced VLBA data at 1.6 GHz revealsflat-spectrum, compact cores (down to a few milliJansky) in four of thefive sources. The absolute astrometry provided by the phase referencingallows us to identify the center of activity on the VLA images.Moreover, these data reveal rich structures, including two-sided jetsand secondary components. On the basis of the arcsecond scale structuresand of the nuclear properties, we rule out the presence of strongrelativistic effects in our LPCs, which must be intrinsically small(deprojected linear sizes 10 kpc). Fits of continuous injectionmodels reveal break frequencies in the GHz domain, and ages in the range10 5{-}107 yrs. In LPCs, the outermost edge may beadvancing more slowly than in more powerful sources or could even bestationary; some LPCs might also have ceased their activity. In general,the properties of LPCs can be related to a number of reasons, including,but not limited to: youth, frustration, low kinematic power jets, andshort-lived activity in the radio.
| Radio sources in low-luminosity active galactic nuclei. IV. Radio luminosity function, importance of jet power, and radio properties of the complete Palomar sample
We present the completed results of a high resolution radio imagingsurvey of all ( 200) low-luminosity active galactic nuclei (LLAGNs) andAGNs in the Palomar Spectroscopic Sample of all ( 488) bright northerngalaxies. The high incidences of pc-scale radio nuclei, with impliedbrightness temperatures ≳107 K, and sub-parsec jetsargue for accreting black holes in ≳50% of all LINERs andlow-luminosity Seyferts; there is no evidence against all LLAGNs beingmini-AGNs. The detected parsec-scale radio nuclei are preferentiallyfound in massive ellipticals and in type 1 nuclei (i.e. nuclei withbroad Hα emission). The radio luminosity function (RLF) of PalomarSample LLAGNs and AGNs extends three orders of magnitude below, and iscontinuous with, that of “classical” AGNs. We find marginalevidence for a low-luminosity turnover in the RLF; nevertheless LLAGNsare responsible for a significant fraction of present day massaccretion. Adopting a model of a relativistic jet from Falcke &Biermann, we show that the accretion power output in LLAGNs is dominatedby the kinetic power in the observed jets rather than the radiatedbolometric luminosity. The Palomar LLAGNs and AGNs follow the samescaling between jet kinetic power and narrow line region (NLR)luminosity as the parsec to kilo-parsec jets in powerful radio galaxies.Eddington ratios {l_Edd} (=L_Emitted/L_Eddington) of≤10-1{-}10-5 are implied in jet models of theradio emission. We find evidence that, in analogy to Galactic black holecandidates, LINERs are in a “low/hard” state (gas poornuclei, low Eddington ratio, ability to launch collimated jets) whilelow-luminosity Seyferts are in a “high” state (gas richnuclei, higher Eddington ratio, less likely to launch collimated jets).In addition to dominating the radiated bolometric luminosity of thenucleus, the radio jets are energetically more significant thansupernovae in the host galaxies, and are potentially able to depositsufficient energy into the innermost parsecs to significantly slow thegas supply to the accretion disk.
| The mass distribution in early type disk galaxies
We are studying the mass distribution in a sample of 50 early typespiral galaxies, with morphological type between S0 and Sab and absolutemagnitudes M_B between -18 and -22; they form the massive andhigh-surface brightness extreme of the disk galaxy population. Our studyis designed to investigate the relation between dark and luminous matterin these systems, of which very little yet is known.From a combination of WSRT HI observations and long-slit opticalspectra, we have obtained high-quality rotation curves. The rotationvelocities always rise very fast in the center; in the outer regions,they are often declining, with the outermost measured velocity 10-25%lower than the maximum.We decompose the rotation curves into contributions from the luminous(stellar and gaseous) and dark matter. The stellar disks and bulgesalways dominate the rotation curves within the inner few disk scalelengths, and are responsible for the decline in the outer parts. As anexample, we present here the decompositions for UGC 9133. We are able toput tight upper and lower limits on the stellar mass-to-light ratios.
| Evidence for Interactions in H I Imaging of Seyfert Galaxies
We still do not know the primary trigger of local active galacticnuclei. Tidal torques and nuclear bars are often invoked to explain gasinfall onto the central supermassive black hole, but as yet neither hasdefinitive observational support. Here we exploit the sensitivity andendurance of H I to trace the strength and prevalence of tidalinteractions among Seyfert galaxies. To minimize selection biases, wesurvey the 27 northern Seyferts compiled in the comprehensive opticalcatalog of Véron-Cetty & Véron lying in the narrowredshift range 0.015-0.017. This paper is a detailed presentation of asubsample, including channel maps for all systems. In addition to theprogram objects, we also investigate galaxies imaged in the field.
| Stacking Searches for Gamma-Ray Emission above 100 MeV from Radio and Seyfert Galaxies
The EGRET telescope on board Compton Gamma Ray Observatory detected morethan 60 sources of high-energy gamma radiation associated with activegalactic nuclei (AGNs). All but one of those belong to the blazarsubclass; the only exception is the nearby radio galaxy Centaurus A.Since there is no obvious reason other than proximity to expect Cen A tobe the only nonblazar AGN emitting in high-energy gamma rays, we haveutilized the ``stacking'' technique to search for emission above 100 MeVfrom two nonblazar AGN subclasses, radio galaxies and Seyfert galaxies.Maps of gamma-ray counts, exposure, and diffuse background have beencreated, then co-added in varying numbers based on sorts by redshift, 5GHz flux density, and optical brightness, and finally tested forgamma-ray emission. No detection significance greater than 2 σ hasbeen found for any subclass, sorting parameter, or number of objectsco-added. Monte Carlo simulations have also been performed to validatethe technique and estimate the significance of the results.
| Motion and properties of nuclear radio components in Seyfert galaxies seen with VLBI
We report EVN, MERLIN and VLBA observations at 18 cm, 6 cm and 3.6 cm ofthe Seyfert galaxies NGC 7674, NGC5506, NGC 2110 and Mrk1210 to study their structure and proper motions on pc scalesand to add some constraints on the many possible causes of theradio-quietness of Seyferts. The component configurations inNGC 7674 and NGC 2110 are simple,linear structures, whereas the configurations in NGC5506 and Mrk 1210 have multiple componentswith no clear axis of symmetry. We suggest that NGC7674 is a low-luminosity compact symmetric object. Comparingthe images at different epochs, we find a proper motion in NGC7674 of (0.92±0.07) c between the two centralcomponents separated by 282 pc and, in NGC 5506, wefind a 3 σ upper limit of 0.50 c for the components separated by3.8 pc. Our results confirm and extend earlier work showing that theoutward motion of radio components in Seyfert galaxies isnon-relativistic on pc scales. We briefly discuss whether thisnon-relativistic motion is intrinsic to the jet-formation process orresults from deceleration of an initially relativistic jet byinteraction with the pc or sub-pc scale interstellar medium. We combinedour sample with a list compiled from the literature of VLBI observationsmade of Seyfert galaxies, and found that most Seyfert nuclei have atleast one flat-spectrum component on the VLBI scale, which was not seenin the spectral indices measured at arcsec resolution. We found alsothat the bimodal alignment of pc and kpc radio structures displayed byradio galaxies and quasars is not displayed by this sample of Seyferts,which shows a uniform distribution of misalignment between0° and 90°. The frequent misalignmentcould result from jet precession or from deflection of the jet byinteraction with gas in the interstellar medium.
| Decametric survey of discrete sources in the Northern sky. XIIIb. Spectra of discrete sources in the declination zone from +300 to +400
New data obtained in the course of the decametric survey of the Northernsky with the UTR-2 radiotelescope in the declination zone from+300 to +400 were used together with data fromhigh-frequency radio surveys to construct spectra for 62 radio sourcesin the frequency range from 12.6 to 50000 MHz. Spectra plots andparameters for these radio sources are given together with statisticalanalysis.
| Unifying B2 radio galaxies with BL Lacertae objects
In an earlier paper we presented nuclear X-ray flux densities, measuredwith ROSAT, for the B2 bright sample of nearby low-luminosity radiogalaxies. In this paper we construct a nuclear X-ray luminosity functionfor the B2 radio galaxies, and discuss the consequences of our resultsfor models in which such radio galaxies are the parent population of BLLacertae (BL Lac) objects. Based on our observations of the B2 sample,we use Monte Carlo techniques to simulate samples of beamed radiogalaxies, and use the selection criteria of existing samples of BL Lacobjects to compare our simulated results to what is observed. We findthat previous analytical results are not applicable since the BL Lacsamples are selected on beamed flux density. A simple model in which BLLacs are the moderately beamed (γ~ 3) counterparts of radiogalaxies, with some random dispersion (~0.4 decades) in the intrinsicradio-X-ray relationship, can reproduce many of the features of theradio-selected and X-ray-selected BL Lac samples, including their radioand X-ray luminosity functions and the distributions of theirradio-to-X-ray spectral indices. In contrast, models in which the X-rayand radio emission have systematically different beaming parameterscannot reproduce important features of the radio-galaxy and BL Lacpopulations, and recently proposed models in which the radio-to-X-rayspectral index is a function of source luminosity cannot in themselvesaccount for the differences in the slopes of the radio- andX-ray-selected BL Lac luminosity functions. The redshift distributionand number counts of the X-ray-selected Einstein Medium SensitivitySurvey (EMSS) sample are well reproduced by our best models, supportinga picture in which these objects are beamed Fanaroff-Riley type I radiogalaxies with intrinsic luminosities similar to those of the B2 sample.However, we cannot match the redshift distribution of the radio-selected1-Jy sample, and it is likely that a population of Fanaroff-Riley typeII radio galaxies is responsible for the high-redshift objects in thissample, in agreement with previously reported results on the sample'sradio and optical emission-line properties.
| Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| High-energy sources before INTEGRAL. INTEGRAL reference catalog
We describe the INTEGRAL reference catalog which classifies previouslyknown bright X-ray and gamma-ray sources before the launch of INTEGRAL.These sources are, or have been at least once, brighter than ~ 1 mCrababove 3 keV, and are expected to be detected by INTEGRAL. This catalogis being used in the INTEGRAL Quick Look Analysis to discover newsources or significantly variable sources. We compiled several publishedX-ray and gamma-ray catalogs, and surveyed recent publications for newsources. Consequently, there are 1122 sources in our INTEGRAL referencecatalog. In addition to the source positions, we show an approximatespectral model and expected flux for each source, based on which wederive expected INTEGRAL counting rates. Assuming the default instrumentperformances and at least ~ 105 s exposure time for anypart of the sky, we expect that INTEGRAL will detect at least ~ 700sources below 10 keV and ~ 400 sources above 20 keV over the missionlife.The Catalog is available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/411/L59
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| Far-Infrared Census of Starburst-Seyfert Connection
Far-infrared flux densities are newly extracted from the IRAS databasefor the Revised Shapley-Ames and CfA complete samples of Seyfertgalaxies. These data are used to classify the Seyfert galaxies intothose where the far-infrared continuum emission is dominated by theactive galactic nucleus (AGN), circumnuclear starburst, or host galaxy.While AGN-dominant objects consist of comparable numbers of Seyfert 1and 2 galaxies, starburst- and host-dominant objects consistpreferentially of Seyfert 2 galaxies. Thus, in addition to the dustytorus, the circumnuclear starburst region and host galaxy are importantin hiding the broad-line region. Morphologically, starburst-dominantSeyfert galaxies are of later types and more strongly interacting thanAGN-dominant Seyfert galaxies. In a later type galaxy, the AGN centralengine has a lower Eddington luminosity, and the gaseous content ishigher. The gas is efficiently supplied to the starburst via agalaxy-galaxy interaction. Morphologies of host-dominant Seyfertgalaxies are of various types. Since starbursts in Seyfert galaxies areolder than those in classical starburst galaxies, we propose anevolution from starburst to starburst-dominant Seyfert to host-dominantSeyfert for a late-type galaxy. An evolution from AGN-dominant Seyfertto host-dominant Seyfert is proposed for an early-type galaxy. Thesesequences have durations of a few times 108 yr and occurrepeatedly within a galaxy during its evolution from a late type to anearly type.
| Redshifts for a Sample of Radio-selected Poor Clusters
Multifiber optical spectroscopy has been performed on galaxies in thevicinity of strong, nearby radio galaxies. These radio galaxies wereselected from the 3CR and B2 catalogs based on their exclusion from theAbell catalog, which is puzzling given the hypothesis that an externalmedium is required to confine the radio plasma of such galaxies.Velocities derived from the spectra were used to confirm the existenceof groups and poor clusters in the fields of most of the radio galaxies.We find that all radio galaxies with classical Fanaroff-Riley type Imorphologies prove to reside in clusters, whereas the other radiogalaxies often appear to be recent galaxy-galaxy mergers in regions oflow galaxy density. These findings confirm the earlier result that theexistence of extended X-ray emission combined with a statistical excessof neighboring galaxies can be used to identify poor clusters associatedwith radio galaxies.
| A new list of extra-galactic radio jets
A catalogue of extra-galactic jets is very useful both in observationaland theoretical studies of active galaxies. With the use of new powerfulradio instruments, the detailed structures of very compact or weak radiosources are investigated observationally and many new radio jets aredetected. In this paper, we give a list of 661 radio sources withdetected radio jets known to us prior to the end of December 2000. Allreferences are collected for the observations of jets in radio, IR,optical, UV and X-ray wave-bands. Table 1 and references to Table 1 areonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/757
| A catalogue and analysis of X-ray luminosities of early-type galaxies
We present a catalogue of X-ray luminosities for 401 early-typegalaxies, of which 136 are based on newly analysed ROSAT PSPC pointedobservations. The remaining luminosities are taken from the literatureand converted to a common energy band, spectral model and distancescale. Using this sample we fit the LX:LB relationfor early-type galaxies and find a best-fit slope for the catalogue of~2.2. We demonstrate the influence of group-dominant galaxies on the fitand present evidence that the relation is not well modelled by a singlepower-law fit. We also derive estimates of the contribution to galaxyX-ray luminosities from discrete-sources and conclude that they provideLdscr/LB~=29.5ergs-1LBsolar-1. Wecompare this result with luminosities from our catalogue. Lastly, weexamine the influence of environment on galaxy X-ray luminosity and onthe form of the LX:LB relation. We conclude thatalthough environment undoubtedly affects the X-ray properties ofindividual galaxies, particularly those in the centres of groups andclusters, it does not change the nature of whole populations.
| Radio Continuum Survey of an Optically Selected Sample of Nearby Seyfert Galaxies
We have used the Very Large Array (VLA) to conduct a survey for radiocontinuum emission in the sample of 52 Seyfert nuclei selected from theoptical spectroscopic galaxy catalog of Ho, Filippenko, & Sargent.This Seyfert sample is the most complete and least biased available,and, as such, it will be useful for a variety of statistical analyses.Here we present the observations, measurements, and an atlas of radiomaps. The observations were made at 6 cm in the B array and at 20 cm inthe A array, yielding matched angular resolutions of ~1". We detected 44objects (85%) at 6 cm and 37 objects (71%) at 20 cm above a 3 σthreshold of 0.12 mJy beam-1. The sources have a wide rangeof radio powers (P~1018-1025 W Hz-1),spectral indices (α206~+0.5 to -1), andlinear sizes (L~few tens pc-15 kpc). The morphology of the radioemission is predominantly that of a compact core, either unresolved orslightly resolved, occasionally accompanied by elongated, jetlikefeatures. Linearly polarized emission was detected at 6 cm in 12sources, nine of which were also detected at 20 cm.
| Statistical Properties of Radio Emission from the Palomar Seyfert Galaxies
We have carried out an analysis of the radio and optical properties of astatistical sample of 45 Seyfert galaxies from the Palomar spectroscopicsurvey of nearby galaxies. We find that the space density of brightgalaxies (-22 mag<=MBT<=-18 mag) showingSeyfert activity is (1.25+/-0.38)×10-3Mpc-3, considerably higher than found in other Seyfertsamples. Host galaxy types, radio spectra, and radio source sizes areuncorrelated with Seyfert type, as predicted by the unified schemes foractive galaxies. Approximately half of the detected galaxies have flator inverted radio spectra, more than expected based on previous samples.Surprisingly, Seyfert 1 galaxies are found to have somewhat strongerradio sources than Seyfert 2 galaxies at 6 and 20 cm, particularly amongthe galaxies with the weakest nuclear activity. We suggest that thisdifference can be accommodated in the unified schemes if a minimum levelof Seyfert activity is required for a radio source to emerge from thevicinity of the active nucleus. Below this level, Seyfert radio sourcesmight be suppressed by free-free absorption associated with the nucleartorus or a compact narrow-line region, thus accounting for both theweakness of the radio emission and the preponderance of flat spectra.Alternatively, the flat spectra and weak radio sources might indicatethat the weak active nuclei are fed by advection-dominated accretiondisks.
| VLBI Observations of a Complete Sample of Radio Galaxies: 10 Years Later
A complete sample of 27 radio galaxies was selected from the B2 and 3CRcatalogs in order to study their properties on the milliarcsecond scale.In the Appendix of this paper we present new radio images for 12 ofthem. Thanks to the present data, all the sources in this sample havebeen imaged at milliarcsecond resolution. We discuss the generalresults. In particular we stress the evidence for high-velocity jets inlow-power radio galaxies, compare high- and low-power sources, anddiscuss the source properties in light of the unified scheme models. Weconclude that the properties of parsec-scale jets are similar in sourceswith different total radio power and kiloparsec-scale morphology. Fromthe core-total radio power correlation, we estimate that relativisticjets with Lorentz factor γ in the range 3-10 are present in high-and low-power radio sources. We discuss also the possible existence of atwo-velocity structure (fast spine and lower velocity external shearlayer).
| Where is the[O III] λ4363 Emitting Region in Active Galactic Nuclei?
The emission-line flux ratio of [O III] λ4363/[O III]λ5007 (RO III) is a useful diagnostic for theionization mechanism and physical properties of emission-line regions inactive galactic nuclei (AGNs). However, it is known that simplephotoionization models underpredict the [O III] λ4363 intensity,being inconsistent with observations. In this paper we report on severalpieces of evidence that a large fraction of the [O III] λ4363emission arises from the dense gas obscured by putative tori: (1) thevisibility of high-RO III regions is correlated to that ofbroad-line regions, (2) higher RO III objects show hottermid-infrared colors, (3) higher RO III objects show strongerhighly ionized emission lines such as [Fe VII] λ6087 and [Fe X]λ6374, and (4) higher RO III objects have broader linewidth of [O III] λ4363 normalized by that of [O III]λ5007. To estimate how such a dense component contributes to thetotal emission-line flux, dual-component photoionization modelcalculations are performed. It is shown that the observed values ofRO III of type 1 AGNs may be explained by introducing a5%-20% contribution from the dense component, while those of type 2 AGNsmay be explained by introducing a 0%-2% contribution. We also discussthe [O III] λ4363 emitting regions in LINERs in the framework ofour dual-component model.
| Properties of CSS radio sources from 102 MHz interplanetary scintillation observations
Interplanetary scintillation observations of 56 compact steep-spectrumradio sources have been carried out at 102 MHz on the Large PhasedArray, Russia. Observations have shown that 42 sources havelow-frequency cut-offs in their spectra. The physical conditions in thecores of the quasars and radio galaxies studied are estimated.
| Physical Conditions in Steep-Spectrum Radio Sources
Interplanetary scintillation observations of the radio sources 4C 31.04,3C 67, 4C 34.07, 4C 34.09, OE 131, 3C 93.1, OF 247, 3C 147, 3C 173, OI407, 4C 68.08, 3C186, 3C 190, 3C 191, 3C 213.1, 3C 216, 3C 237, 3C 241,4C 14.41, 3C 258, and 3C 266 have been carried out at 102 MHz.Scintillations were detected for nearly all the sources. The integratedflux densities and flux densities of the scintillating components areestimated. Nine of the 21 sources have a low-frequency turnover in theirspectra; three of the sources have high-frequency turnovers. Thephysical parameters are estimated for sources with turnovers in thespectra of their compact components. In most of the quasars, therelativistic-plasma energy exceeds the magnetic-field energy, while theopposite is true of most of the radio galaxies. Empirical relationsbetween the size of the compact radio source and its magnetic field andrelativistic-electron density are derived.
| RBSC-NVSS Sample. I. Radio and Optical Identifications of a Complete Sample of 1556 Bright X-Ray Sources
We cross-identified the ROSAT Bright Source Catalog (RBSC) and the NRAOVLA Sky Survey (NVSS) to construct the RBSC-NVSS sample of the brightestX-ray sources (>=0.1 counts s-1~10-12 ergscm-2 s-1 in the 0.1-2.4 keV band) that are alsoradio sources (S>=2.5 mJy at 1.4 GHz) in the 7.8 sr of extragalacticsky with |b|>15deg and δ>-40deg. Thesky density of NVSS sources is low enough that they can be reliablyidentified with RBSC sources having rms positional uncertainties>=10". We used the more accurate radio positions to make reliableX-ray/radio/optical identifications down to the POSS plate limits. Weobtained optical spectra for many of the bright identifications lackingpublished redshifts. The resulting X-ray/radio sample is unique in itssize (1557 objects), composition (a mixture of nearly normal galaxies,Seyfert galaxies, quasars, and clusters), and low average redshift[~0.1].
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| X-ray Emission Mechanisms of LINERs
We present here an analysis of the X-ray properties of a sample of LINERgalaxies observed with the ROSAT PSPC and HRI instruments. A spatialanalysis shows that the bulk of the X-ray emission is consistent witharising from a point source; some extended emission appears at weakemission levels. The X-ray spectra are formally best described by apowerlaw with photon index Γ_x ~ -2 or thermal emission from aRaymond-Smith plasma with highly subsolar abundances (Z <= 0.1).Several emission mechanisms that might contribute to the observed X-rayspectra are discussed. In particular, we take the very subsolarabundances derived from Raymond-Smith fits as an indication of a morecomplex emission mechanism, like the presence of a second hard componentor plasma out of equilibrium.
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