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A Radio Study of the Seyfert Galaxy Markarian 6: Implications for Seyfert Life Cycles
We have carried out an extensive radio study with the Very Large Arrayon the Seyfert 1.5 galaxy Mrk 6 and imaged a spectacular radio structurein the source. The radio emission occurs on three different spatialscales: ~7.5 kpc bubbles, ~1.5 kpc bubbles lying nearly orthogonal tothem, and a ~1 kpc radio jet lying orthogonal to the kiloparsec-scalebubble. To explain the complex morphology, we first consider a scenarioin which the radio structures are the result of superwinds ejected by anuclear starburst. However, recent Spitzer observations of Mrk 6 providean upper limit to the star formation rate (SFR) of ~5.5Msolar yr-1, an estimate much lower than the SFRof ~33 Msolar yr-1 derived assuming that thebubbles are a result of starburst winds energized by supernovaexplosions. Thus, a starburst alone cannot meet the energy requirementsfor the creation of the bubbles in Mrk 6. We then present anenergetically plausible model wherein the bubbles are a result of energydeposited by the kiloparsec-scale jet as it plows into the interstellarmedium. Finally, we consider a model in which the complex radiostructure is a result of an episodically powered precessing jet thatchanges its orientation. This model is the most attractive as it cannaturally explain the complex radio morphology and is consistent withthe energetics, the spectral index, and the polarization structure.Radio emission in this scenario is a short-lived phenomenon in thelifetime of a Seyfert galaxy, which results from an accretion event.
| The Jet and Circumnuclear Environment of 3C 293
We present new HST NIR polarimetry, broadband and narrowband imaging,and MERLIN 4.5 GHz multifrequency synthesis radio imaging of 3C 293, aunique radio galaxy whose host is an obvious merger remnant, in anexceptionally underdense region of space. We have discovered NIR,optical, and UV synchrotron emission from the jet. In the optical, thejet is mostly obscured by a dust lane, but three knots are clear in ourHST NICMOS images at 1.6 and 2.0 μm, clearly aligning with featuresin the radio. The outer jet knot is highly polarized (~15%) at 2 μm,confirming the synchrotron emission mechanism. The radio-IR spectralindex steepens significantly with distance from the nucleus, as in 3C273 and in contrast to M87. The inner knot is visible (with hindsight)on the WFPC2 and STIS images obtained for the earlier 3CR HST snapshotsurveys. There is no [Fe II] emission seen associated with the jet,constraining the role of shock-induced ionization by the jet. Overallthere is a strong implication that the NIR jet emission is indeedsynchrotron. From our NIR images, the core of the galaxy is clearlyidentifiable with the main feature in the western extension of the radio``jet'' image, although no unresolved AGN component is identifiable evenat K band, consistent with an FR II-like nucleus obscured by anoptically thick torus. The galaxy appears to have a single nucleus, withany multiple nuclei falling within the central <~100 pc.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 (AURA), Inc.,under NASA contract NAS5-26555.Based on observations with MERLIN, a national facility operated by theUniversity of Manchester on behalf of PPARC in the UK.
| The lifecycles of powerful radio galaxies: Triggering and feedback
I review the links between host galaxy evolution and quasar/jet activityin radio galaxies from an observational standpoint. Observations of thewarm ionized gas provide evidence for powerful outflows in both theextended emission line regions (EELR: 5 < r < 100 kpc) and thenarrow line regions (NLR: r < 5 kpc) that are capable of directlyinfluencing the evolution of the stellar populations in the hostgalaxies. There is also evidence that the distribution of circum-nuclearISM undergoes significant evolution as the radio jets expand through thecentral bulges of the hosts. On the other hand, results for the youngstellar populations in the host galaxies provide key information aboutthe triggering merger events. They indicate that there can be asignificant time lag between the major episode of merger-induced starformation and triggering of the radio jets, and that some ultraluminousinfrared galaxies may evolve into radio galaxies.
| The relation between mergers and AGN activity. Results from radio galaxy and luminous infrared galaxy studies
There is morphological evidence that the activity in powerful radiogalaxies could be triggered by mergers and galaxy interactions. However,nothing is known about the timescales, order of events, and the type ofinteraction involved. It is not yet known whether there exists anevolutionary link between radio galaxies and other merger systems suchas very luminous and ultraluminous infrared galaxies (VLIRGs andULIRGs). Here, we report preliminary results obtained from the analysisof near-ultraviolet and optical spectroscopic observations of samples ofRadio Galaxies and VLIRGs-ULIRGs to investigate, through age-dating oftheir young stellar population, whether an evolutionary link existsbetween VLIRGs/ULIRGs-Radio Galaxies-normal elliptical galaxies. Theseresults will help to understand the genesis events that lead to theformation of radio jet and quasar activity, and they will allow us toplace radio galaxies in the context of hierarchical evolution models forthe population of giant elliptical galaxies.
| 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.
| The Spiral Host Galaxy of the Double Radio Source 0313-192
We present new Hubble Space Telescope (HST), Gemini South, and Chandraobservations of the radio galaxy 0313-192, which hosts a 350 kpc doublesource and jets, even though previous data have suggested that it is aspiral galaxy. We measure the bulge scale and the luminosity, radial,and vertical profiles of disk starlight and consider the distributionsof H II regions and absorbing dust. In each case the HST data confirmits classification as an edge-on spiral galaxy, the only such systemknown to produce such an extended radio source of this kind. The Gemininear-IR images and Chandra spectral fit reveal a strongly obscuredcentral active galactic nucleus (AGN), seen through the entireinterstellar medium path length of the disk and showing X-ray evidenceof additional absorption from warm or dense material close to thecentral object. We consider several possible mechanisms for producingsuch a rare combination of AGN and host properties, some combination ofwhich may be at work. These include an unusually luminous bulge(suggesting a black hole of mass ~8×108Msolar), the orientation of the jets near the pole of thegas-rich disk, and some evidence of a weak gravitational interactionthat has warped the disk and could have enhanced fueling of the centralengine. We detect an X-ray counterpart of the kiloparsec-scale radio jetemerging to the south; jet/counterjet limits on both radio and X-rayregimes allow them to be symmetric if seen more than 15° from theplane of the sky, still consistent with the jet axes being within~30° of the poles of the gas-rich galaxy disk. A linear or disklikeemission-line structure is seen around the nucleus, inclined by ~20°to the stellar disk but nearly perpendicular to the jets; this mayrepresent the aftermath of a galaxy encounter, in which gas isphotoionized by a direct view of the nuclear continuum.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy (AURA), Inc.,under NASA contract NAS5-26555 made with the Chandra X-Ray Observatory;and obtained at the Gemini Observatory, which is operated by AURA, Inc.,under a cooperative agreement with the National Science Foundation (NSF)on behalf of the Gemini partnership: the NSF (United States), theParticle Physics and Astronomy Research Council (United Kingdom), theNational Research Council (Canada), CONICYT (Chile), the AustralianResearch Council (Australia), CNPq (Brazil), and CONICET (Argentina).
| Timescales of merger, starburst and AGN activity in radio galaxy B2 0648+27
We use neutral hydrogen (H I) and optical spectroscopic observations tocompare the timescales of a merger event, starburst episode andradio-AGN activity in the radio galaxy B2 0648+27. Wedetect a large ring-like structure of H I in emission around theearly-type host galaxy of B2 0648+27 (MH I= 8.5 × 109~Mȯ, diameter = 190 kpc). Weinterpret this as the result of a major merger that occurred ≳1.5Gyr ago. From modelling optical long-slit spectra we find that a youngstellar population of 0.3 Gyr, indicative of a past starburst event,dominates the stellar light throughout the galaxy. The off-set in timebetween the merger event and the starburst activity in B20648+27 suggests that the starburst was triggered in anadvanced stage of the merger, which can be explained if the gas-richprogenitor galaxies contained a bulge. Although the exact age of theradio source remains uncertain, there appears to be a significanttime-delay between the merger/starburst event and the current episode ofradio-AGN activity. We also observe an outflow of emission-line gas inthis system, which is likely related to superwinds driven by the starsthat formed during the starburst event. We argue that the radio galaxyB2 0648+27 is a link in the evolutionary sequencebetween Ultra-Luminous Infrared Galaxies (ULIRGs) and genuine early-typegalaxies.
| The Chandra view of the 3C/FR I sample of low luminosity radio-galaxies
We present results from Chandra observations of the 3C/FR I sample oflow luminosity radio-galaxies. We detected a power-law nuclear componentin 12 objects out of the 18 with available data. In 4 galaxies wedetected nuclear X-ray absorption at a level of NH (0.2{-}6) × 1022 cm-2. X-ray absorbedsources are associated with the presence of highly inclined dusty disks(or dust filaments projected onto the nuclei) seen in the HST images.This suggests the existence of a flattened X-ray absorber, but of muchlower optical depth than in classical obscuring tori. We thus have anunobstructed view toward most FR I nuclei, while absorption plays only amarginal role in the remaining objects. Three pieces of evidence supporta jet origin for the X-ray cores: i) the presence of strong correlationsbetween the nuclear luminosities in the radio, optical, and X-ray bands,extending over 4 orders of magnitude and having a much smallerdispersion ( 0.3 dex) when compared to similar trends found for otherclasses of AGNs, all of which points to a common origin for the emissionin the three bands; ii) the close similarity of the broad-band spectralindices with the sub-class of BL Lac objects sharing the same range ofextended radio-luminosity, in accord with the FR I/BL Lacs unifiedmodel; iii) the presence of a common luminosity evolution of spectralindices in both FR I and BL Lacs. The low luminosities of the X-raynuclei, regardless of their origin, strengthens the interpretation oflow efficiency accretion in low luminosity radio-galaxies.
| The host galaxy/AGN connection in nearby early-type galaxies. Is there a miniature radio-galaxy in every "core" galaxy?
This is the second of a series of three papers exploring the connectionbetween the multiwavelength properties of AGN in nearby early-typegalaxies and the characteristics of their hosts. We selected two sampleswith 5 GHz VLA radio flux measurements down to 1 mJy, reaching levels ofradio luminosity as low as 1036 erg s-1. In PaperI we presented a study of the surface brightness profiles for the 65objects with available archival HST images out of the 116 radio-detectedgalaxies. We classified early-type galaxies into "core" and "power-law"galaxies, discriminating on the basis of the slope of their nuclearbrightness profiles, following the Nukers scheme. Here we focus on the29 core galaxies (hereafter CoreG). We used HST and Chandra data toisolate their optical and X-ray nuclear emission. The CoreG invariablyhost radio-loud nuclei, with an average radio-loudness parameter of LogR = L5 {GHz} / LB 3.6. The optical and X-raynuclear luminosities correlate with the radio-core power, smoothlyextending the analogous correlations already found for low luminosityradio-galaxies (LLRG) toward even lower power, by a factor of 1000, covering a combined range of 6 orders of magnitude. This supportsthe interpretation of a common non-thermal origin of the nuclearemission also for CoreG. The luminosities of the nuclear sources, mostlikely dominated by jet emission, set firm upper limits, as low asL/L_Edd 10-9 in both the optical and X-ray band, on anyemission from the accretion process. The similarity of CoreG and LLRGwhen considering the distributions host galaxies luminosities and blackhole masses, as well as of the surface brightness profiles, indicatesthat they are drawn from the same population of early-type galaxies.LLRG represent only the tip of the iceberg associated with (relatively)high activity levels, with CoreG forming the bulk of the population. Wedo not find any relationship between radio-power and black hole mass. Aminimum black hole mass of M_BH = 108 Mȯ isapparently associated with the radio-loud nuclei in both CoreG and LLRG,but this effect must be tested on a sample of less luminous galaxies,likely to host smaller black holes. In the unifying model for BL Lacsand radio-galaxies, CoreG likely represent the counterparts of the largepopulation of low luminosity BL Lac now emerging from the surveys at lowradio flux limits. This suggests the presence of relativistic jets alsoin these quasi-quiescent early-type "core" galaxies.
| A jet-induced outflow of warm gas in 3C293
Using long-slit emission-line spectra we detect a fast outflow ofionized gas, with velocities up to 1000 km s-1, in the nearbypowerful radio galaxy 3C293 (z= 0.045). The fast outflow is locatedabout 1 kpc east of the nucleus, in a region of enhanced radio emissiondue to the presence of a distorted radio jet. We present results thatindicate that this fast outflow is caused by a jet-ISM interaction. Thekinematics of the outflowing ionized gas are very similar to those of afast outflow of neutral hydrogen gas in this galaxy, suggesting thatboth outflows are the result of the same driving mechanism. While themass of the outflowing ionized gas is about 1 ×105Msolar, the total HI mass involved in theneutral outflow is about 100 times higher(107Msolar). This shows that, despite the highenergies that must be involved in driving the outflow, most of the gasremains, or again becomes, neutral. Other outflows of ionized gas,although not as pronounced as in the region of the enhanced radioemission, are also seen in various other regions along the axis of theinner radio jets. The regular kinematics of the emission-line gas alongthe major axis of the host galaxy reveals a rotating ionized gas disc 30kpc in extent.
| Starbursts and the triggering of the activity in nearby powerful radio galaxies
We present high-quality long-slit spectra for three nearby powerfulradio galaxies - 3C 293, 3C 305 and PKS 1345+12. These were taken withthe aim of characterizing the young stellar populations (YSP), andthereby investigating the evolution of the host galaxies, as well as theevents that triggered the activity. Isochrone spectral synthesismodelling of the wide wavelength coverage spectra of nuclear andoff-nuclear continuum-emitting regions have been used to estimate theages, masses and luminosities of the YSP component, taking full accountof reddening effects and potential contamination by activity-relatedcomponents. We find that the YSP make a substantial contribution to thecontinuum flux in the off-nuclear regions on a radial scale of 1-20 kpcin all three objects. Moreover, in two objects we find evidence forreddened post-starburst stellar populations in the near-nuclear regionsof the host galaxies. The YSP are relatively old (0.1-2 Gyr), massive(109 < MYSP < 2 × 1010Msolar) and make up a large proportion (~1-50 per cent) ofthe total stellar mass in the regions of the galaxies sampled by theobservations. Overall, these results are consistent with the idea thatthe nuclear activity of active galactic nuclei in some radio galaxies istriggered by major gas-rich mergers. Therefore, these radio galaxiesform part of the subset of early-type galaxies that is evolving mostrapidly in the local Universe. Intriguingly, the results also suggestthat the radio jets are triggered relatively late in the mergersequence, and that there is an evolutionary link between radio galaxiesand luminous/ultraluminous infrared galaxies.
| Molecular Gas and Nuclear Activity in Radio Galaxies Detected by IRAS
This paper reports the latest results from a millimeter-wave (CO)spectroscopic survey of IRAS-detected radio galaxies withL1.4GHz~1023-1028 W Hz-1 inthe redshift range z~0.02-0.15. The IRAS flux-limited sample contains 33radio galaxies with different radio morphologies and a broad range ofinfrared luminosities (LIR=109-1012Lsolar), allowing for an investigation of (1) whether low-zradio-selected active galactic nuclei (AGNs) reside in moleculargas-rich host galaxies and (2) whether the CO properties are correlatedwith the properties of the host galaxy or the AGN. All of the radiogalaxies in Mazzarella et al. and Mirabel et al. have been reobserved.Three new CO detections have been made, raising the total number of COdetections to nine and setting the survey detection rate at ~25%. Manyof the CO lines have double-peaked profiles, and the CO line widths arebroad (average ΔvFWHM~500+/-130 km s-1),exceeding the average CO widths of both ultraluminous infrared galaxies(300+/-90 km s-1) and Palomar-Green QSOs (260+/-160 kms-1), and thus being indicative of massive host galaxies. TheCO luminosities translate into molecular gas masses of~(0.4-7)×109 Msolar, however, the 3 σCO upper limits for nondetections do not rule out a molecular gas massas high as that of the Milky Way (~3×109Msolar). Optical images of eight out of nine moleculargas-rich radio galaxies show evidence of close companions and/or tidalfeatures. Finally, there is no obvious correlation between radio powerand molecular gas mass. However, it is notable that only one F-R IIgalaxy out of 12 is detected in this CO survey; the remaining detectionsare of galaxies hosting F-R I and compact radio jets.
| Observational Evidence of Jet Precession in Galactic Nuclei Caused by Accretion Disks
We show that the observational data of extragalactic radio sources tendto support the theoretical relationship between the jet precessionperiod and the optical luminosity of the sources, as predicted by themodel in which an accretion disk causes the central black hole toprecess.
| Outflows in Active Galactic Nucleus/Starburst-Composite Ultraluminous Infrared Galaxies1,
Galactic superwinds occur in almost all infrared-luminous galaxies withstar formation rates (SFRs) above 10 Msolar yr-1,as shown by studies of the Na I D interstellar absorption line. Wedemonstrate that this result also applies to ultraluminous infraredgalaxies (ULIRGs) that host an active galactic nucleus (AGN) embedded ina strong starburst (SFR>~100 Msolar yr-1) bystudying a sample of 26 Seyfert ULIRGs in Na I D. The infraredluminosity of these galaxies is powered jointly by the AGN andstarburst. We find that there are hints of the influence of the AGN onoutflows in Seyfert 2/starburst composites, but the evidence is not yetstatistically conclusive. The evidence we find is lower wind detectionrates (i.e., wind opening angles) in Seyfert 2 ULIRGs than in galaxiesof comparable LIR, higher velocities than in galaxies ofcomparable SFR, and correlations between the neutral gas and the ionizedgas in the extended narrow-line region. Although the AGN probablycontributes to the outflows in Seyfert 2 ULIRGs, its momentum and energyinjection is equal to or less than that of the starburst. Similarly, theoutflow mechanical luminosity (energy outflow rate) per unit radiativeluminosity is the same for starburst and Seyfert 2 ULIRGs. In the nucleiof Seyfert 1 ULIRGs, we observe small-scale outflows that are poweredsolely by the AGN. However, in Mrk 231, we observe both a high-velocity,small-scale and low-velocity, extended outflow. The latter may bepowered by a starburst or radio jet. These large-scale, lower velocityoutflows certainly exist in other Seyfert 1 ULIRGs, but they are washedout by the light of the nucleus.Some of the observations reported here were obtained at the MMTObservatory, which is a joint facility of the Smithsonian Institutionand the University of Arizona.Some of the observations reported here were obtained at the Kitt PeakNational Observatory, National Optical Astronomy Observatory, which isoperated by the Association of Universities for Research in Astronomy(AURA), Inc., under cooperative agreement with the National ScienceFoundation.
| The Hubble Space Telescope View of LINER Nuclei: Evidence for a Dual Population?
We study a complete, distance-limited sample of 25 LINERs, 21 of whichhave been imaged with the Hubble Space Telescope. In nine objects wedetect an unresolved nucleus. To study their physical properties, wecompare the radio and optical properties of the nuclei of LINERs withthose of other samples of local active galactic nuclei (AGNs), namely,Seyfert galaxies and low-luminosity radio galaxies (LLRGs). Our resultsshow that the LINER population is not homogeneous, as there are twosubclasses: (1) the first class is similar to the LLRG class, as itextends the population of radio-loud nuclei to lower luminosities; (2)the second is similar to Seyfert galaxies and extends the properties ofradio-quiet nuclei toward the lowest luminosities. The objects areoptimally discriminated in the plane formed by the black hole massversus nuclear radio loudness: all radio-loud LINERs haveMBH>~108Msolar, while Seyfertgalaxies and radio-quiet LINERs haveMBH<~108Msolar. The different natureof the various classes of local AGNs are best understood when thefraction of the Eddington luminosity they irradiate,Lo/LEdd, is plotted against the nuclearradio-loudness parameter: Seyfert galaxies are associated withrelatively high radiative efficienciesLo/LEdd>~10-4 (and high accretionrates onto low-mass black holes); LLRGs are associated with lowradiative efficiencies (and low accretion rates onto high-mass blackholes); all LINERs have low radiative efficiency (and accretion rates)and can be radio-loud or radio-quiet, depending on their black holemass.Based on observations obtained at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.
| 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.
| Fast neutral outflows in powerful radio galaxies: a major source of feedback in massive galaxies
We report the detection of fast (~1000 km s-1), massiveoutflows of neutral gas observed - using the WSRT - as 21-cm H Iabsorption against the strong radio continuum of seven radio sources.The neutral outflows occur, in at least somes cases, at kpc distancefrom the nucleus, and they are most likely driven by the interactionsbetween the expanding radio jets and the gaseous medium enshrouding thecentral regions. We estimate that the associated mass outflow rates areup to ~50 Mȯ yr-1, comparable (although atthe lower end of the distribution) to the outflow rates found forstarburst-driven superwinds in Ultra Luminous IR Galaxies (ULIRG). Thissuggests that massive, jet-driven outflows of neutral gas in radio-loudAGN can have as large an impact on the evolution of the host galaxies asthe outflows associated with starbursts. A radio-loud phase of the AGNis likely a relatively common, albeit short, phase in the life of many(or even all) massive ellipticals. Jet-driven neutral outflows mayrepresent one of the main feedback mechanisms in these galaxies.
| The location of the broad H i absorption in 3C 305: clear evidence for a jet-accelerated neutral outflow
We present high-spatial resolution 21-cm H i VLA observations of theradio galaxy 3C 305 (z=0.041). These new high-resolution data show thatthe 1000 km s-1 broad H I absorption, earlier detectedin low-resolution WSRT observations, is occurring against the bright,eastern radio lobe, about 1.6 kpc from the nucleus. We use new opticalspectra taken with the WHT to make a detailed comparison of thekinematics of the neutral hydrogen with that of the ionised gas. Thestriking similarity between the complex kinematics of the two gas phasessuggests that both the ionised gas and the neutral gas are part of thesame outflow. Earlier studies of the ionised gas had already foundevidence for a strong interaction between the radio jet and theinterstellar medium at the location of the eastern radio lobe. Ourresults show that the fast outflow produced by this interaction alsocontains a component of neutral atomic hydrogen. The most likelyinterpretation is that the radio jet ionises the ISM and accelerates itto the high outflow velocities observed. Our observations demonstratethat, following this strong jet-cloud interaction, not all gas cloudsare destroyed and that part of the gas can cool and become neutral. Themass outflow rate measured in 3C 305 is comparable, although at thelower end of the distribution, to that found in Ultra-Luminous IRgalaxies. This suggests that AGN-driven outflows, and in particularjet-driven outflows, can have a similar impact on the evolution of agalaxy as starburst-driven superwinds.
| High-resolution imaging of the radio continuum and neutral gas in the inner kiloparsec of the radio galaxy 3C 293
Using a combination of observations involving the Very Large Array(VLA), MERLIN and global Very Long Baseline Interferometry (VLBI)networks we have made a detailed study of the radio continuum and theneutral hydrogen (HI) kinematics and distribution within the centralkiloparsec of the radio galaxy 3C 293. These observations trace thecomplex jet structure and identify the position of the steeply invertedradio core at 1.3 GHz.Strong HI absorption is detected against the majority of the innerkiloparsec of 3C 293. This absorption is separated into two dynamicallydifferent and spatially resolved systems. Against the eastern part ofthe inner radio jet, narrow HI absorption is detected and shown to havehigher optical depths in areas cospatial with a central dust lane.Additionally, this narrow line is shown to follow a velocity gradient of~50 km s-1 arcsec-1, consistent with the velocitygradient observed in optical spectroscopy of ionized gas. We concludethat the narrow HI absorption, dust and ionized gas are physicallyassociated and situated several kiloparsecs from the centre of the hostgalaxy. Against the western jet emission and core component, broad andcomplex HI absorption is detected. This broad and complex absorptionstructure is discussed in terms of two possible interpretations for thegas kinematics observed. We explore the possibility that these broad,double absorption spectra are the result of two gas layers at differentvelocities and distances along these lines of sight. A second plausibleexplanation for this absorbing structure is that the HI is situated inrotation about the core of this radio galaxy with some velocitydispersion resulting from infall and outflow of gas from the coreregion. If the latter explanation were correct, then the mass enclosedby the rotating disc would be at least 1.7 × 109 solarmasses within a radius of 400 pc.
| No evidence for a different accretion mode for all 3CR FR I radio galaxies
We have analysed the optical and radio properties of a sample of 3CR FRI radio galaxies which have Hubble Space Telescope (HST) imaging capableof detecting optical cores. The jet powers of the FR I radio galaxiesare estimated from their low-frequency radio luminosities, and theoptical core luminosity is taken as an upper limit on the emission fromany unobscured accretion disc. We argue that if the accretion discs inthese sources are assumed to be advection-dominated accretion flows(ADAFs), or adiabatic inflow-outflow solution (ADIOS) flows, then theBlandford-Znajek mechanism provides insufficient power to explain thehigh radio luminosities of at least a third, and perhaps all, of thesample. We suggest instead that a significant fraction (the`high-jet-power' third), and perhaps most, of the 3CR FR I radiogalaxies have normal accretion discs, but that their optical cores canbe hidden, with any HST-detected optical synchrotron emission comingfrom jets on scales larger than the obscuring material. A normalaccretion disc hypothesis, at least for the high-jet-power third of the3CR FR Is, explains why narrow-line luminosity correlates with radioluminosity. It also explains why one object in the sample (3C 386) hasan observed broad-line nucleus. We conclude that there is no evidence tosuggest that there is a difference in accretion mode between FR I and FRII radio galaxies.
| Dust in 3CR radio galaxies: On the FR 1 - FR 2 difference
We compare three 3CR samples of 11 FR 1 galaxies, 17 FR 2 galaxies and18 lobe-dominated quasars contained in the ISO Data Archive. In contrastto the powerful FR 2 galaxies with edge-brightened lobes, the low radiopower FR 1 galaxies in our sample do not exhibit any high MIR or FIRdust luminosity, which is typical for a buried, intrinsically moreluminous AGN. This consolidates the fact already inferred from opticalstudies that their AGNs have only a relatively low luminosity. Also theFR 1 galaxies show a high FIR/MIR luminosity ratio, compared to quasars,suggesting that their FIR luminosity is substantially powered by theinterstellar radiation field (ISRF) of the giant elliptical hosts.Finally, we discuss the FR 1 - FR 2 morphological dichotomy. FR 1galaxies do not have more interstellar matter (ISM) than FR 2s as traced- on the large scale - by the cool FIR emitting dust and - in thenuclear region - by the warm MIR emitting dust. Due to the lack ofcentral gas we suggest that the black holes of our FR 1 galaxies are fedat a lower accretion rate than those of the FR 2 galaxies.Based on observations with the Infrared Space Observatory ISO, an ESAproject with instruments funded by ESA Member States (especially the PIcountries: France, Germany, the Netherlands and the UK) and with theparticipation of ISAS and NASA.
| ISOCAM survey and dust models of 3CR radio galaxies and quasars
We present a survey of all 3CR sources imaged with ISOCAM onboard theInfrared Space Observatory (ISO). The sample consists mostly ofradio-loud active galactic nuclei (AGN). For each source, we presentspatially integrated mid-infrared (MIR, 5-18 μm) fluxes measured fromnewly calibrated ISOCAM images. In total, we detected 68 objects of the3CR catalogue, at redshifts z ≤2.5, and obtained upper limits for 17objects. In addition, we detected 10 galaxies not listed in the 3CRcatalogue. The one with the highest redshift is 4C+72.26 at z = 3.53.ISOCAM data are combined with other photometric measurements toconstruct the spectral energy distribution (SED) from optical to radiowavelengths. The MIR emission may include synchrotron radiation of theAGN, stars of the host galaxy or dust. Extrapolation of radio corefluxes to the MIR show that the synchrotron contribution is in mostcases negligible. In order to describe dust emission we apply newradiative transfer models. In the models the dust is heated by a centralsource which emits photons up to energies of 1 keV. By varying threeparameters, luminosity, effective size and extinction, we obtain a fitto the SED for our objects. Our models contain also dust at large(several kpc) distances from the AGN. Such a cold dust component wasneglected in previous computations which therefore underestimated theAGN contribution to the far infrared (FIR). In 53 cases ( 75% ofour detected 3CR sources), the MIR emission can be attributed to dust.The hot dust component is mainly due to small grains and PAHs. Themodelling demonstrates that AGN heating suffices to explain the ISObroad band data, starburst activity is not necessary. In the models, atype 1 AGN is represented by a compact dust distribution, the dust istherefore very warm and emission of PAHs is weak because ofphoto-destruction. In AGNs of type 2, the dust is relatively colder butPAH bands are strong.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) with the participation of ISAS and NASA.Appendices A and B are only available in electronic form athttp://www.edpsciences.org
| Observations of the neutral gas and dust in the radio galaxy 3C 305
We present MERLIN and Hubble Space Telescope (HST) observations of thecentral region of the nearby radio galaxy 3C 305 and use them to studythe gas and dust in this object. The MERLIN observations are of neutralhydrogen (HI) absorption against the strong non-thermal 20 cm continuumseen towards the central 4 kpc of 3C 305. Our ~0.2 arcsec (160 pc)resolution observations show that the HI absorption is highly localizedagainst the south-western radio-emission with column densities ~1.9× 1021 cm-2. The absorption is broad (fullwidth at half maximum, FWHM, of 145 +/- 26 km s-1) andredshifted by 130 km s-1 relative to the systemic velocity.The HST images in multiple optical and infrared filters (430 nm, 702 nm,[OIII] 500.7 nm, [FeII] 1.64 μm and K-band polarization) arepresented. Evidence is seen for coincidence of the [FeII] emission withthe knot at the end of the radio jet, which is evidence for the presenceof shocks.We compare the optical and radio images in order to investigate therelationship between the dust and neutral gas distributions. Anunresolved (0.07 arcsec) nucleus is detected in H and K and itsproperties are consistent with a quasar reddened by AV >4. We propose that the absorption arises in a region of neutral gas anddust. Its structure is complex but is broadly consistent with aninclined disc of gas and dust encircling, but not covering, the activegalactic nucleus. A comparison of the neutral gas observations andprevious emission-line observations suggests that both the neutral andionized gas are undergoing galactic rotation towards the observer in thenorth-east and away from the observer in the south-west. We propose thatthe outflow giving rise to the radio emission has a component towardsthe observer in the north-east and away from the observer in thesouth-west. Unfortunately, as we do not detect radio emission from thecompact nucleus, we cannot set limits to neutral hydrogen absorptionfrom a circumnuclear obscuring torus.
| Supernova 2003jb in IC 1065
IAUC 8259 available at Central Bureau for Astronomical Telegrams.
| Supernovae 2003jb, 2003jc, 2003jd, and 2003je
IAUC 8232 available at Central Bureau for Astronomical Telegrams.
| Hot Dust in Radio-loud Active Galactic Nuclei
We have measured mid-infrared (MIR) fluxes of 3C sources on images takenwith ISOCAM on board the Infrared Space Observatory (ISO). Thephotometric data were combined with existing photometry at otherwavelengths to assemble the spectral energy distribution (SED) for eachgalaxy from infrared to radio wavelengths. In addition, we used ISOPHOTspectra to compute average MIR spectra for different types of activegalactic nuclei (AGNs). The MIR emission of 53 of our sources showsevidence of dust. We find a clear correlation between the SEDs, emissionfrom polycyclic aromatic hydrocarbons (PAHs), and the type of AGN.Specifically, we find that in broad emission line radio galaxies(BLRGs), the dust emission peaks at λ~40 μm and PAH bands areweak, whereas emission in comparable narrow-line radio galaxies (NLRGs)peaks at a longer wavelength of λ~100 μm and the PAH bands aremuch stronger. Although less pronounced, a similar trend is seen whencomparing QSOs with high-luminosity NLRGs. We used dust radiativetransfer models with a central heating source to describe the SEDs. Thedifference in the dust emission appears to be the effect of heating byradiation from the central engine. In type 1 AGNs (BLRGs and QSOs), thebroad-line region (BLR) is directly visible, and therefore hot(T>~300 K) dust dominates the emission. In this region, PAHs aredestroyed, which explains the weak PAH emission. On the other hand, theBLR is hidden in type 2 AGNs (NLRGs). Their SEDs are therefore dominatedby cooler dust, including PAHs.
| Fast Outflow of Neutral Hydrogen in the Radio Galaxy 3C 293
We report the detection of very broad H I absorption against the centralregions of the radio galaxy 3C 293. The absorption profile, obtainedwith the Westerbork Synthesis Radio Telescope, has a full width at zerointensity of about 1400 km s-1, and most of this broadabsorption (~1000 km s-1) is blueshifted relative to thesystemic velocity. This absorption represents a fast outflow of neutralgas from the central regions of this active galactic nucleus. Possiblecauses for such an outflow are discussed. We favor the idea that theinteraction between the radio jet and the rich interstellar mediumproduces this outflow. Some of the implications of this scenario areconsiderebd.Based on observations with the Westerbork Synthesis Radio Telescope.
| 870 Micron Observations of Nearby 3CRR Radio Galaxies
We present submillimeter continuum observations at 870 μm of thecores of low-redshift 3CRR radio galaxies, observed at the HeinrichHertz Submillimeter Telescope. The cores are nearly flat-spectrumbetween the radio and submillimeter, which implies that thesubmillimeter continuum is likely to be synchrotron emission and notthermal emission from dust. The emitted power from nuclei detected atoptical wavelengths and in the X-rays is similar in the submillimeter,optical, and X-rays. The submillimeter-to-optical and X-ray power ratiossuggest that most of these sources resemble misdirected BL Lac-typeobjects with synchrotron emission peaking at low energies. However, wefind three exceptions, the FR I galaxy 3C 264 and the FR II galaxies 3C390.3 and 3C 338 with high X-ray-to-submillimeter luminosity ratios.These three objects are candidate misdirected high- orintermediate-energy peaked BL Lac-type objects. With additional infraredobservations and from archival data, we compile spectral energydistributions for a subset of these objects. The steep dips observednear the optical wavelengths in many of these objects suggest thatextinction inhibits the detection and reduces the flux of opticalcontinuum core counterparts. High-resolution near- or mid-infraredimaging may provide better measurements of the underlying synchrotronemission peak.
| The Ultraviolet Continuum Emission of FR I and FR II Radio Galaxies and a Proposal for a Unified AGN Model for FR I sources
This paper is the second in a series of two on the UV continuum emission(in the range from 1400 to 3700 Å) of radio galaxies that wereextracted from the Hubble Space Telescope (HST) Archives. The sampleconsists of 31 3C and Parkes radio galaxies that have redshifts below0.2 (the majority have redshifts of ~0.03) and radio powers of~1025-1027 W Hz-1 (usingH0=50 km-1 s-1 Mpc andq0=0.0). Paper I describes the sample selection and theproperties of individual sources; this paper deals with the analysis. Wefind that only about half the radio galaxies display any UV flux atwavelengths shorter than 2300 Å. More specifically, those galaxiesthat are dominated by a nuclear UV component are either BL Lac objectsor radio galaxies with broad emission lines. We detect a nuclear and anextended UV component only among half the radio galaxies with narrowemission lines. Although we do not find a correlation of the UVluminosity with emission-line luminosity or radio power, there doesappear to be a dependence on radio morphology. While (narrow line) FR IIsources do not show a nuclear UV component, FR I's do, however, only ifthey also have an optical jet (this is the case for seven of 21 FR I's).These results are broadly consistent with orientation-dependentunification models. In radio galaxies in which the torus does notobscure our view of the engine, the observed UV radiation appears to bepoint source-like. This is the case for broad-line radio galaxies and BLLac objects. In other radio galaxies that are oriented at an angle tous, the torus presumably blocks the nuclear UV component. Thenarrow-line FR I galaxies with optical jets can then be interpreted asobjects at a critical angle at which some, but not all, nuclear UVemission is blocked. The UVλ luminosities (withλ ranging from 1400 to 3700 Å) and theUVλ-V colors of radio galaxies show a larger scatterthan those of radio-quiet elliptical galaxies. At wavelengths shorterthan 2300 Å, some radio galaxies have on average bluer colors, butbeyond 3000 Å, their colors are on average slightly redder. Thispicture is also consistent with unification models-the galaxies withbluer colors are either BL Lac objects or broad-line radio galaxies. Allother radio galaxies (including the jetted FR I's) have somewhat reddercolors than radio-quiet elliptical galaxies. We suspect that this isprimarily due to reddening by dust, which we know is present in some ofthe radio galaxies in the sample. At longer wavelengths (>3000 Å),all radio galaxies (14 of 14) show an extended component. The morphologyof the extended emission is in most, but not all, cases comparable tothe morphology at optical wavelengths, implying that this is likely tobe starlight. However, the polarization images of two of seven radiogalaxies indicate that scattered light from the active galactic nucleusmay also contribute toward the UV luminosity.
| 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
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