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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.
| 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.
| 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 transition in the accretion properties of radio-loud active nuclei
We present evidence for the presence of a transition in the accretionproperties of radio-loud sources. For a sample of radio galaxies andradio-loud quasars, selected based on their extended radio properties,the accretion rate is estimated from the black hole mass and nuclearluminosity. The inferred distribution is bimodal, with a paucity ofsources at accretion rates, in Eddington units, of the order of~10-2- assuming a radiative efficiency of 10 per cent - andpossibly spanning 1-2 orders of magnitude. Selection biases are unlikelyto be responsible for such behaviour. We discuss possible physicalexplanations, including a fast transition to low accretion rates, achange in the accretion mode/actual accretion rate/radiative efficiency,the lack of stable disc solutions at intermediate accretion rates or theinefficiency of the jet formation processes in geometrically thin flows.This transition might be analogous to spectral states (and jet)transitions in black hole binary systems.
| 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.
| 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.
| Surface photometry of radio loud elliptical galaxies from the B2 sample
V-band CCD imaging is presented for 72 galaxies from the B2 radio sample(Colla et al. \cite{colla}; Fanti et al. \cite{fanti78}), with redshiftsup to 0.2 and radio powersP408=1023-1026.5 W Hz-1.According to the morphology on the optical images 57 galaxies areclassified as ellipticals, 6 as spirals and 7 as irregular. Surfacephotometry of the sample of ellipticals was obtained fitting ellipses tothe light distribution. The light profile of these galaxies generallyfollows a de Vaucouleurs law, although in three cases the profiles showlarge excesses relative to the r1/4 law at large radii. Thefitted mu_e and r_e parameters for the de Vaucouleurs galaxies are givenin the paper. Three of the ellipticals show a bright nucleus. One ofthem is a known broad line radio galaxy (B2 1833+32) and the remainingtwo are Markarian galaxies, classified in the literature as BL Lacobjects (B2 1101+38 and B2 1652+39). The radial profiles forellipticity, position angle, and B_4 term of the Fourier analysis arepresented in the paper, and the morphological peculiarities of theellipticals are described, including the presence of shells, tails,nuclear dust, isophote twisting, off-centering, and boxiness or disknessof the isophotes. Only one of the galaxies in this work is included inthe subsample of B2 radio galaxies with well-defined jets (Parma et al.\cite{parma87}). In this sense the present sample complements the sampleof 24 radio galaxies with well-defined radio jets in Parma et al. forwhich a similar study was presented in González-Serrano et al.(\cite{gserrano93}). The irregular galaxy B2 0916+33 appears to bemisclassified, and we suggest that the right identification of the radiosource is a nearby point like object with V=18.45 mag. The spiral galaxyassociated with B2 1441+26 is also misclassified. A point-like opticalobject with V=18.88 mag, located at ~ 36 arcsec from the originalidentification and coincident with the radio core is the most probablecounterpart. Table 4 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html Complete Figure 1 and Figure 2are only available at http://www.edpsciences.org
| The HST snapshot survey of the B2 sample of low luminosity radio-galaxies: a picture gallery
A Hubble Space Telescope snapshot survey of the B2 sample of lowluminosity radio galaxies has, at present, produced V and I images of 41objects. Together with 16 images of B2 sources taken from the HSTarchive, there are now high resolution optical data for ~ 57% of thesample. All host galaxies are luminous ellipticals, except one which isa spiral galaxy, while another one turns out to be a misidentification.We present an album of the images of the B2 radio galaxies observed sofar, and give a brief description of the optical morphology of thegalaxies. Dust features (in the form of disks, lanes or irregularpatches) are seen in most of the galaxies of the sample, ~ 58%. Compactoptical cores are also very common (18/57). A preliminary analysis hasrevealed the presence of an optical jet in three objects, indicatingthey can be detected in a sizeable percentage in these low luminosityradio sources. Brightness profiles of dust-free galaxies are wellrepresented by a Nuker law and all shows the existence of a resolvedshallow cusp. 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
| Weak Radio Galaxies. II. Narrow-Band Optical Imaging and Physical Conditions
Not Available
| Weak Radio Galaxies. I. Broad-Band Optical Imaging
We report on a study of the optical properties of weak radio galaxies(WRGs) from the B2 survey, to obtain the broad-band photometricproperties and morphology information crucial for our narrow-bandimaging at Hα and [O III] study (Carrillo et al. 1997). This papercontains optical CCD images of 30 radio galaxies obtained at V, R and I.We present the morphological and photometric results and discuss theirrelationship to the radio structure and environmental properties. Wefind that most WRGs are E galaxies, have peculiar morphologies and arelocated in high galaxy density environments. Optical colors of WRGs areunusual if compared to colors of normal ellipticals, but similar to AGNcolors. The surface brightness profiles of most WRGs follow the deVaucouleurs law expected for ellipticals at most radii, but in all casesa turnover or flatness is observed in the innermost portion of theprofiles, possibly produced by an additional nuclear emission source.The tidal effects produced by galaxy companions described by Kormendy(1977) for ellipticals, are clearly evident in the outer parts of theWRGs profiles and can be associated to interaction effects.
| Galaxy structures in the Hercules region
216 redshifts have been obtained in a region of 981 sq deg south of theHercules supercluster. 172 of these redshifts are of galaxies withmpg less than or equal to 15.1, 110 of which had no previousvelocity measurement. 44 new redshifts are of galaxies fainter thanmpg = 15.1. With these new data we have been able to define asample in a vast region (approximately 1700 sq deg) around Herculeslimited to mpg less than or equal to 15.1 with a velocitycompleteness of 81.5%. 189 galaxies have been morphologically classifiedso that all galaxies in the sample with known velocity now also haveknown morphology. The magnitude limited sample, including 556 galaxies,is then used to identify and describe galaxy structures in the region.We find that the overdense volume is small, that its overall appearanceis that of a coral branch floating in a sea of nothing and that earlyand late type galaxies defined different structures.
| Energy distributions of radio galaxies
Far-infrared observations of 140 radio galaxies which span a range ofover four orders of magnitude in radio power, (from weak nuclear sourcesin nearby galaxies, to powerful FR II doubled lobed sources at moderateredshift) are presented. The strength of the far-infrared emission ismore closely correlated with core than total radio emission.Far-infrared emission in radio galaxies represents star formation thatis more closely tied to the active nucleus than to the global propertiesof the galaxy. The far-infrared luminosity function shows goodcontinuity between radio galaxies and radio loud quasars.
| Observations of faint radio galaxies with the Ratan-600 radio telescope
The results of observations of 79 faint radio galaxies from the BolognaSurvey with the RATAN-600 radio telescope at the frequency 3.95 GHz arepresented. The dependences of spectral indices of radio emission on theratio of radio and optical luminosities are analyzed. The dependence oflinear sizes of radio galaxies on these ratios and on spectral indiceswas studied. It is shown that median angular sizes and spectral indicesincrease with flux density. It is also shown that among radio galaxieswith flat spectra objects of small linear sizes (less than 10 kpc) occurmuch more frequently than among radio galaxies with steep spectra.
| Radio nuclei in elliptical galaxies
Observations at 4.9 GHz with the VLA are presented for 36 radio galaxiesof the B2 and 3C catalog, with no previous core flux measurement: 24cores were detected, while for the others stringent upper limits aregiven. The statistical properties of the radio cores in ellipticalgalaxies are then analyzed, using a sample of 187 radio galaxies, whichcover a power range from 10 to the 23rd to 10 to the 28th W/Hz.Correlations are found between the core power and the total power andbetween the core power and the optical absolute magnitude, in agreementwith previous results; no redshift dependence is found of the twocorrelations. The existence of radio galaxies with upper limits to thecore flux well below the value expected from the Pc-Pt correlationsuggests that these could be relic radio sources, where the nucleus hasceased its activity.
| VLA observations of low-luminosity radio galaxies. VI - Discussion of radio jets
The B2 source sample of low luminosity radio galaxies, which is used forthe present statistical study of the properties of jets, contains about100 objects, and has been reobserved at 1.4 GHz using three differentconfigurations of the VLA. Unambiguous evidence is found for thepresence of jets in 45 percent of the sources. The fraction of sourceswith jets decreases with increasing source power; the less powerfulradio galaxies are noted to have the more symmetric jets. Jet propertiesare discussed in terms of the Bicknell (1984, 1985) model.
| VLA observations of low luminosity radio galaxies. I - Sources with angular size smaller than two arcminutes
Fifty-seven radio sources with angular size smaller than about twoarcmin, selected from two complete samples of low luminosity B2 radiogalaxies, have been observed at 20 cm with the VLA in the Bconfiguration, with an angular resolution of about 3.5 arcsec. Thereduction procedure is described and the quality of the radio maps isdiscussed. The dynamic range in the final CLEANed maps is usually around100:1 or better. Observational parameters and intrinsic propertiesderived for each source are given in separate tables. Contour maps arepresented for resolved sources. Information on individual sources isprovided, particularly in case of interesting structures.
| Statistical properties of the radio cores in elliptical galaxies
A statistical study of the properties of the radio cores in ellipticalgalaxies has been performed on a sample of 138 radio galaxies taken fromthe B2 and 3CR catalogues. About two-thirds of these objects have adetected core at 5 GHz. A statistically significant correlation is foundbetween the core and the total radio power. However, the largedispersion around the best fit regression line implies that the coreradio power is not a good indicator of the total radio power. Moreover,a correlation is found between the core radio power and the opticalabsolute magnitude: optically brighter galaxies tend to have higher coreradio powers. Within the limited redshift range of the present sample,no redshift dependence of the two correlations is found.
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