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Spectral Variability of Quasars in the Sloan Digital Sky Survey. II. The C IV Line
We examine the variability of the high-ionization C IV λ1549 linein a sample of 105 quasars observed at multiple epochs by the SloanDigital Sky Survey. We find a strong correlation between the change inthe C IV line flux and the change in the line width, but no correlationsbetween the change in flux and changes in line center and skewness. Therelation between line flux change and line width change is consistentwith a model in which a broad line base varies with greater amplitudethan the line core. The objects studied here are more luminous and athigher redshift than those normally studied for variability, ranging inredshift from 1.65 to 4.00 and in absolute r-band magnitude from roughly-24 to -28. Using moment analysis line-fitting techniques, we measureline fluxes, centers, widths, and skewnesses for the C IV line at twoepochs for each object. The well-known Baldwin effect is seen for theseobjects, with a slope of β=-0.22. The sample has a median intrinsicBaldwin effect slope of βint=-0.85 the C IV lines inthese high-luminosity quasars appear to be less responsive to continuumvariations than those in lower luminosity AGNs. In addition, we find noevidence for variability of the well-known blueshift of the C IV linewith respect to the low-ionization Mg II λ2798 line in thehighest flux objects, indicating that this blueshift might be useful asa measure of orientation.Presented as part of a dissertation to the Department of Astronomy andAstrophysics of the University of Chicago, in partial fulfillment of therequirements for the Ph.D. degree.
| Merger origin of radio galaxies investigated with H I observations
We present results of an H I study of a complete sample of nearby radiogalaxies. Our goal is to investigate whether merger or interactionevents could be at the origin of the radio-AGN activity. Around five ofour radio galaxies, hosted mainly by early-type galaxies, we detectextended H I in emission. In most cases this H I is distributed in large(up to 190 kpc) and massive (up to M_HI 1010Mȯ) disk- or ring-like structures, that show fairlyregular rotation around the host galaxy. This suggests that in thesesystems a major merger likely occurred, but at least several Gyr ago.For the H I-rich radio galaxy B2 0648+27 we confirm such a merger originthrough the detection of a post-starburst stellar population thatdominates the visible light throughout this system. The timescale of thecurrent episode of radio-AGN activity in our H I- rich radio galaxies isseveral orders of magnitude smaller than the merger timescales.Therefore the radio-AGN activity either started late in the lifetime ofthe merger event, or is not directly related to the merger event at all.Another intriguing result is that the H I- rich (> 109Mȯ) radio galaxies in our sample all have compact radiosources, while none of the extended radio sources contain these amountsof extended H I. This strongly suggests that there is a relation betweenthe size of the radio jet and the presence of large amounts of neutralgas associated with the host galaxy.
| Gamma-ray emissions of AGN and cosmological standard candles
In this work, we compile a sample which contains 71 GeV Gamma-ray-loudActive Galactic Nuclei (AGNs) (14 BL Lacs and 57 FSRQs), 53 FR I radiogalaxies and 63 FR II radio galaxies. We make a nonlinear least-squarefit to this sample, and find that the best fit value of the Hubbleconstant is H0=71.5±3.8 kms-1Mpc-1 with a reduced χ ~= 2.46 by assumingMv = -23.0 and accepting q0 = 1.0, and thecorresponding regression line has a correlation index R ~= 0.78. Thebest fit value of H0 = 71.5±3.8 kms-1Mpc-1 is in well agreement with H0 =72±8 km s-1 obtained by the Hubble Space TelescopeKey Project. Our results show that the GeV Gamma-ray emissions of AGNscan be used as cosmological standard candles indeed.
| 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 HST view of the nuclear emission line region in low luminosity radio-galaxies
We study the properties of the emission line regions in two samples oflow luminosity radio-galaxies, while focusing on the Compact EmissionLine Region (CELR) revealed to be a characteristic feature of theseobjects by HST narrow-band imaging. We find a strong correlation betweenline and optical continuum nuclear emission, which suggests that theoptical cores (most likely of non-thermal origin) can be directlyassociated to the source of ionizing photons, i.e. that we are seeing ajet-ionized narrow line region. A photon budget argument indicates thatthe optical nuclear sources produce sufficient photon flux provided thatthe covering factor of the circum-nuclear gas is rather large, onaverage 0.3. Analysis of HST images and spectra suggests that the CELRmay take the form of a pc-scale, high filling factor structure, possiblyan optically thin torus. Estimates of the CELR mass lead to values assmall as 10{-}10^3 Mȯ, and photon counting sets a limitto the Broad Line Region mass of M_BLR < 10-2Mȯ. When considered together with the low accretion rateand the tenuous torus structure, a general paucity of gas in theinnermost regions of low luminosity radio-galaxies emerges as the maincharacterizing difference from more powerful Active Galactic Nuclei.
| Are radio galaxies and quiescent galaxies different? Results from the analysis of HST brightness profiles
We present a study of the optical brightness profiles of early typegalaxies, using a number of samples of radio galaxies and opticallyselected elliptical galaxies. For the radio galaxy samples - B2 ofFanaroff-Riley type I and 3C of Fanaroff-Riley type II - we determined anumber of parameters that describe a "Nuker-law" profile, which werecompared with those already known for the optically selected objects. Wefind that radio active galaxies are always of the "core" type (i.e. aninner Nuker law slope γ < 0.3). However, there are core-typegalaxies which harbor no significant radio source and which areindistinguishable from the radio active galaxies. We do not find anyradio detected galaxy with a power law profile (γ > 0.5). Thisdifference is not due to any effect with absolute magnitude, since in aregion of overlap in magnitude the dichotomy between radio active andradio quiescent galaxies remains. We speculate that core-type objectsrepresent the galaxies that have been, are, or may become, radio activeat some stage in their lives; active and non-active core-type galaxiesare therefore identical in all respects except their eventualradio-activity: on HST scales we do not find any relationship betweenboxiness and radio-activity. There is a fundamental plane, defined bythe parameters of the core (break radius rb and breakbrightness μ_b), which is seen in the strong correlation betweenrb and μ_b. The break radius is also linearly proportionalto the optical Luminosity in the I band. Moreover, for the few galaxieswith an independently measured black hole mass, the break radius turnsout to be tightly correlated with MBH. The black hole masscorrelates even better with the combination of fundamental planeparameters rb and μ_b, which represents the centralvelocity dispersion.
| A dichotomy in the orientation of dust and radio jets in nearby low-power radio galaxies
We examine the properties of central dust in nearby quiescent and activeearly-type galaxies. The active galaxies are low-power radio galaxieswith Fanaroff & Riley type I or I/II radio jets. We focus on (a) thecomparison of the dust distributions in the active and quiescent galaxysamples; and (b) the relation between the radio jet and dustorientations. Our main observational conclusions are: (i) in line withprevious studies, the dust detection rate is higher in radio-jetgalaxies than in non radio-jet galaxies; (ii) radio galaxies contain ahigher fraction of regular dust “ellipses” compared toquiescent galaxies which contain more often irregular dustdistributions; (iii) the morphology, size and orientation of dustellipses and lanes in quiescent early-types and active early-types withkpc-scale radio jets is very similar; (iv) dust ellipses are alignedwith the major axis of the galaxy, dust lanes do not show a preferredalignment except for large (>kpc) dust lanes which are aligned withthe minor axis of the galaxy; and (v) as projected on the sky, jets donot show a preferred orientation relative to the galaxy major axis (andhence dust ellipses), but jets are preferentially perpendicular to dustlanes. We show that the dust ellipses are consistent with being nearlycircular thin disks viewed at random viewing angles. The lanes arelikely warped dust structures, which may be in the process of settlingdown to become regular disks or are being perturbed by anon-gravitational force. We use the observed dust-jet orientations toconstrain the three-dimensional angle θDJ between jetand dust. For dust-lane galaxies, the jet is approximately perpendicularto the dust structure, while for dust-ellipse galaxies there is a muchwider distribution of θDJ. We discuss two scenariosthat could explain the dust/jet/galaxy orientation dichotomy. If lanesare indeed settling, then the jet orientation apparently is roughlyaligned with the angular momentum of the dust before it settles. Iflanes are perturbed by a jet-related force, it appears that it causesthe dust to move out of its equilibrium plane in the galaxy into a planewhich is perpendicular to the jet.
| Construction of a Celestial Coordinate Reference Frame from VLBI Data
A large number (2 million) of VLBI observations have been reducedin order to refine the measured coordinates of the observed radiosources. The data reduction was carried out in the OCCAM package usingthe least squares colocation method. Corrections to the coordinates of642 objects were derived. The accuracy of the catalog is no worse than0.2 milliseconds of arc for stable sources.
| 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.
| Optical nuclei of radio-loud AGN and the Fanaroff-Riley divide
We investigate the nature of the point-like optical nuclei that havebeen found in the centres of the host galaxies of a majority of radiogalaxies by the Hubble Space Telescope. We examine the evidence thatthese optical nuclei are relativistically beamed, and look fordifferences in the behaviour of the nuclei found in radio galaxies ofthe two Fanaroff-Riley types. We also attempt to relate this behaviourto the properties of the optical nuclei in their highly beamedcounterparts (the BL Lac objects and radio-loud quasars) as hypothesizedby the simple Unified Scheme. Simple model-fitting of the data suggeststhat the emission may be coming from a non-thermal relativistic jet. Itis also suggestive that the contribution from an accretion disk is notsignificant for the FRI objects and for the narrow-line radio galaxiesof FRII type, while it may be significant for the Broad-line objects,and consistent with the idea that the FRII optical nuclei seem to sufferfrom extinction due to an obscuring torus while the FRI optical nucleido not. These results are broadly in agreement with the Unified Schemefor radio-loud AGNs.Appendix C is only available in electronic form athttp://www.edpsciences.org
| 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.
| Space Telescope Imaging Spectrograph Spectroscopy of the Emission-Line Gas in the Nuclei of Nearby FR-I Galaxies
We present the results of the analysis of a set of medium-resolutionspectra, obtained by the Space Telescope Imaging Spectrograph on boardthe Hubble Space Telescope, of the emission-line gas present in thenuclei of a complete sample of 21 nearby, early-type galaxies with radiojets (the UGC FR-I Sample). For each galaxy nucleus we presentspectroscopic data in the region of Hα and the derived kinematics.We find that in 67% of the nuclei the gas appears to be rotating and,with one exception, the cases where rotation is not seen are eitherface-on or have complex central morphologies. We find that in 62% of thenuclei the fit to the central spectrum is improved by the inclusion of abroad component. The broad components have a mean velocity dispersion of1349+/-345 km s-1 and are redshifted from the narrow linecomponents (assuming an origin in Hα) by 486+/-443 kms-1.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| 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
| Core Radio and Optical Emission in the Nuclei of nearby FR I Radio Galaxies
In this paper we analyze the relation between radio, optical continuumand Hα+[N II] emission from the cores of a sample of 21 nearbyFanaroff and Riley type I galaxies as observed with the VLBA and HST.The emission arises inside the inner tens of parsecs of the galaxies.Core radio emission is observed in 19/20 galaxies, optical corecontinuum emission is detected in 12/21 galaxies and Hα+[N II]core emission is detected in 20/21 galaxies. We confirm the recentlydetected linear correlation between radio and optical core emission inFR I galaxies and show that both core emissions also correlate withcentral Hα+[N II] emission. The tight correlations between radio,optical, and Hα+[N II] core emission constrain the bulk Lorentzfactor to γ~2-5 and γ<~2 for a continuous jet and a jetconsisting of discrete blobs, respectively, assuming jet-viewing anglesin the range 30°-90°. Radio and optical core emissions arelikely to be synchrotron radiation from the inner jet, possibly with asignificant contribution from emission by an accretion disk and/or flow.Elliptical galaxies with LINER nuclei without large-scale radio jetsseem to follow the core emission correlations found in FR I galaxies.This suggests that the central engines could be very similar for the twoclasses of active galactic nuclei. Based on observations with theNASA/ESA Hubble Space Telescope obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| The Orientation of Jets Relative to Dust Disks in Radio Galaxies
We use Hubble Space Telescope broadband images and VLA and VLBIcontinuum data to study the three-dimensional orientation of jetsrelative to nuclear dust disks in 20 radio galaxies. The comparisonbetween the position angles of the jets and those of the dust disk majoraxes shows a wide distribution, suggesting that they are not alignedpreferentially perpendicular to each other. We use a statisticaltechnique to determine the three-dimensional distribution of anglesbetween jets and dust disk rotation axes. This analysis shows that theobservations are consistent with jets homogeneously distributed over alarge region, extending over polar caps of 55°-77° but seemingto avoid lying close to the plane of the dust disks. We argue that thelack of close alignment between jets and dust disks axes is not likelyto be caused by feeding the nucleus with gas from mergers originatedfrom random directions. We suggest that the misalignment can be due to awarping mechanism in the accretion disk, such as self-irradiationinstability or the Bardeen-Petterson effect, or that the gravitationalpotential in the inner regions of the galaxy is misaligned with respectto that of the dust disk. Based partly on observations made with theNASA/ESA Hubble Space Telescope, which is operated by the Association ofUniversities for Research in Astronomy, Inc., under NASA contractNAS5-26555.
| 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.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| HST images of B2 radio galaxies: A link between circum-nuclear dust and radio properties?
Almost 60% of the B2 low luminosity radio galaxies have been observedwith the Hubble Space Telescope. We present an analysis of the dustfeatures, which are often present in the form of circum-nuclear disks orlanes, and show that there are correlations between radio source anddust properties. It is found that nearby radio sources in which a jethas been detected tend to have dust more often than sources withoutjets; the dust is often in the form of disks or lanes. Moreover theradio jets are close to perpendicular to the disk or lane in the weakerradio sources (with P < 1024 WHz-1). Instronger sources the orientation effect appears to be weak or evenabsent. Also the dust masses found in the weaker radio sources aresmaller than in the stronger ones (log M/Msun ~ 3 against 5respectively). More generally it appears that there is a correlationbetween dust mass and total radio power (for those sources in which dusthas been detected); we show that this correlation is not induced byredshift. Based on observations with the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by AURA, Inc., under NASA contract NAS 5-26555 and by STScIgrant GO-3594.01-91A.
| Compact groups in the UZC galaxy sample
Applying an automatic neighbour search algorithm to the 3D UZC galaxycatalogue (Falco et al. \cite{Falco}) we have identified 291 compactgroups (CGs) with radial velocity between 1000 and 10 000 kms-1. The sample is analysed to investigate whether Tripletsdisplay kinematical and morphological characteristics similar to higherorder CGs (Multiplets). It is found that Triplets constitute lowvelocity dispersion structures, have a gas-rich galaxy population andare typically retrieved in sparse environments. Conversely Multipletsshow higher velocity dispersion, include few gas-rich members and aregenerally embedded structures. Evidence hence emerges indicating thatTriplets and Multiplets, though sharing a common scale, correspond todifferent galaxy systems. Triplets are typically field structures whilstMultiplets are mainly subclumps (either temporarily projected orcollapsing) within larger structures. Simulations show that selectioneffects can only partially account for differences, but significantcontamination of Triplets by field galaxy interlopers could eventuallyinduce the observed dependences on multiplicity. Tables 1 and 2 are onlyavailable in electronic at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/391/35
| The HST survey of the B2 sample of radio-galaxies: Optical nuclei and the FR I/BL Lac unified scheme
We examine the optical properties of the nuclei of low luminosityradio-galaxies using snapshot HST images of the B2 sample. In agreementwith the results obtained from the analysis of the brighter 3C/FR Isample, we find a correlation between fluxes (and luminosities) of theoptical and radio cores. This provides further support for theinterpretation that the optical nuclear emission in FR I is dominated bysynchrotron emission and that accretion in these sources takes place ina low efficiency radiative regime. In the framework of the FR I/BL Lacsunified scheme, we find that the luminosity difference between FR I andBL Lac nuclei can be reproduced with a common beaming factor in both theradio and the optical band, independent of the extended radioluminosity, thus supporting such a scenario. The corresponding bulkLorentz factor is significantly smaller than is expected fromobservational and theoretical considerations in BL Lacs: this can beinterpreted as due to a velocity structure in the jet, with a fast spinesurrounded by a slower layer. Based on observations with the NASA/ESAHubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by AURA, Inc., under NASA contract NAS5-26555 and by STScI grant GO-3594.01-91A.
| 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
| 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).
| New Evidence for the Unified Scheme of BL Lacertae Objects and FR I Radio Galaxies
In this paper, we collect radio and X-ray observations for mostFanaroff-Riley I (FR I) radio galaxies in the Zirbel-Baum radio galaxysample and investigate the distribution of the radio-to-X-ray effectivespectral index, αrx, to test the unified scheme of BLLac objects and FR I radio galaxies. It is found that the range ofαrx for FR I radio galaxies is almost the same as thatfor BL Lac objects, that the distribution of αrxprobably peaks at the same position as BL Lac objects, and that thedistribution of αrx for FR I galaxies is similar tothat for BL Lac objects. These suggest that there exist two subclassesof FR I radio galaxies: one is HBL-like, and the other is LBL-like,corresponding to high-energy-peaked (HBL) and low-energy-peaked (LBL) BLLac objects, respectively. This result is consistent with previous VLAobservations and supports the unified scheme of BL Lac objects and FR Iradio galaxies.
| HI observations of loose galaxy groups. I. Data and global properties
At Nançay, 21-cm H I line observations were made of 15spiral-dominated loose groups of galaxies, divided into two samples: an``interacting'' sample containing at least one pair of interactinggalaxies, and a ``control'' sample having no optical evidence ofinteractions or morphological disturbances among the group members. Theinteracting sample consists of 62 galaxies representing 9 differentgroups, and the control sample contains 40 galaxies representing 6groups. Of the 91 galaxy and galaxy pairs observed, 74 were detected,while upper limits were placed on the remaining 17 objects. Thesehomogeneous H I data, which will be used in future analyses, providecomparative information on the H I content of groups and serve as aprobe of the vicinity of the target spirals for H I clouds or very lowsurface brightness gas-rich galaxies.
| Are all radio galaxies genuine ellipticals?
Classical double radio sources are believed to be powered by a strongrelativistic jet due to the presence of a rapidly spinning black hole inthe center of a giant E galaxy formed by the merging of two galaxies. Ifthis is true, no radio source should have been found in spiral or S0galaxies. A number of radio S0s have been reported, but most of them areprobably misclassified Es. However, our own observations confirm thatNGC 612 is an S0 although it is associated with the FR II radio sourcePKS 0131-36. We conclude that S0s can be classical radio sources, butthat such occurences are extremely rare. Partly based on observationsobtained with the ESO 3.6 m telescope, La Silla, Chile.
| 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.
| VLBA Observations of a Sample of Nearby FR I Radio Galaxies
We observed 17 nearby low-luminosity FR I radio galaxies using the NRAOVery Long Baseline Array (VLBA) at 1.67 GHz, as part of amultiwavelength study of a complete sample of 21 sources selected byradio flux density from the Uppsala General Catalogue of Galaxies. Wedetected radio emission from all 17 galaxies. At a FWHM resolution of~10×4 mas, five galaxies show only an unresolved radio core, 10galaxies show core-jet structures, and two galaxies show twin-jetstructures. Comparing these VLBA images with images previously obtainedwith the NRAO VLA, we find that all detected VLBA jets are well alignedon parsec scales with the VLA jets on kiloparsec scales and that thejet-to-counterjet surface brightness ratios, or the sidedness, decreasessystematically with increasing distance along the jet. We attribute thesidedness to the Doppler boosting effect and its decline to thedeceleration of the jets. We show that a distribution of Lorentz factorcentered near Γ=5 can reproduce our VLBA detection statistics forcore, core-jet, and twin-jet sources. We also note that the luminosityper unit length, Lj, of the VLBA jets drops quickly withdistance, r, along the jet, approximately asLj~r-2.0. We discuss three different mechanisms toexplain this jet fading: (1) the decrease of Doppler boosting due to jetdeceleration, (2) synchrotron losses, and (3) expansion losses inconstant velocity but adiabatically spreading jets. Mechanisms (1) and(2) are inconsistent with the observations, while mechanism (3) isconsistent with the observations provided the magnetic field lines inthe jets are aligned perpendicular to the jet axis. This implies thatthe deceleration of the jets required by the unified scheme does notoccur on the tens of parsec scales but must occur on larger scales.
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