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A Chandra Snapshot Survey for 3C Radio Galaxies with Redshifts between 0.3 and 0.5
This paper contains an analysis of short Chandra observations of 19 3Csources with redshifts between 0.3 and 0.5 not previously observed inthe X-rays. This sample is part of a project to obtain Chandra data forall of the extragalactic sources in the 3C catalog. Nuclear X-rayintensities as well as any X-ray emission associated with radio jetknots, hotspots, or lobes have been measured in three energy bands:soft, medium, and hard. Standard X-ray spectral analysis for the fourbrightest nuclei has also been performed. X-ray emission was detectedfor all the nuclei of the radio sources in the current sample with theexception of 3C 435A. There is one compact steep spectrum source whileall the others are FR II radio galaxies. X-ray emission from two galaxyclusters (3C 19 and 3C 320), from six hotspots in four radio galaxies(3C 16, 3C 19, 3C 268.2, 3C 313), and extended X-ray emission onkiloparsec scales in 3C 187 and 3C 313, has been detected.
| Chandra Observations of 3C Radio Sources with z < 0.3. II. Completing the Snapshot Survey
We report on the second round of Chandra observations of the 3C snapshotsurvey developed to observe the complete sample of 3C radio sources withz < 0.3 for 8 ks each. In the first paper, we illustrated the basicdata reduction and analysis procedures performed for the 30 sources ofthe 3C sample observed during Chandra Cycle 9, while here we present thedata for the remaining 27 sources observed during Cycle 12. We measuredthe X-ray intensity of the nuclei and of any radio hot spots and jetfeatures with associated X-ray emission. X-ray fluxes in three energybands, i.e., soft, medium, and hard, for all the sources analyzed arealso reported. For the stronger nuclei, we also applied the standardspectral analysis, which provides the best-fit values of the X-rayspectral index and absorbing column density. In addition, a detailedanalysis of bright X-ray nuclei that could be affected by pile-up hasbeen performed. X-ray emission was detected for all the nuclei of theradio sources in our sample except for 3C 319. Among the current sample,there are two compact steep spectrum radio sources, two broad-line radiogalaxies, and one wide angle tail radio galaxy, 3C 89, hosted in acluster of galaxies clearly visible in our Chandra snapshot observation.In addition, we also detected soft X-ray emission arising from thegalaxy cluster surrounding 3C 196.1. Finally, X-ray emission from hotspots has been found in three FR II radio sources and, in the case of 3C459, we also report the detection of X-ray emission associated with theeastern radio lobe as well as X-ray emission cospatial with radio jetsin 3C 29 and 3C 402.
| Extended soft X-ray emission in 3CR radio galaxies at z < 0.3: high excitation and broad line galaxies
We analyze Chandra observations of diffuse soft X-ray emissionassociated with a complete sample of 3CR radio galaxies at z < 0.3.We focus on the properties of the spectroscopic sub-classes of highexcitation galaxies (HEGs) and broad line objects (BLOs). Among the 33HEGs we detect extended (or possibly extended) emission in about 40% ofthe sources; the fraction is even higher (8/10) when restricting theanalysis to the objects with exposure times larger than 10 ks. In the 18BLOs, extended emission is seen only in two objects; this lowerdetection rate can be ascribed to the presence of their bright X-raynuclei that easily outshine any genuine diffuse emission. A very closecorrespondence between the soft X-ray and optical line morphologyemerges. We also find that the ratio between [O III] and extended softX-ray luminosity is confined within a factor of 2 around a median valueof 5. Both results are similar to what is seen in Seyfert galaxies. Wediscuss different processes that could explain the soft X-ray emissionand conclude that the photoionization of extended gas, coincident withthe narrow line region, is the favored mechanism.Appendix A is available in electronic form at http://www.aanda.org
| The First Polarization Maps from the GMRT
We present the first set of polarimetric images made with the GMRT. Wefind that the instrumental polarization leakage at the GMRT varies withfrequency. It is possible to calibrate these terms to better than 1%accuracy, making it feasible to study sources that are polarized at thefew per cent level. We present 610 MHz polarization images of twoextended FR-II radio galaxies, viz. 3C 79 and 3C 265. We present highresolution polarization images of these two sources and also find thatthe polarization fractions of the two sources as seen at the GMRT areconsistent with those reported by Conway & Strom (1984).
| The 1.6 ?m Near-infrared Nuclei of 3C Radio Galaxies: Jets, Thermal Emission, or Scattered Light?
Using HST NICMOS 2 observations we have measured 1.6 ?m near-infrarednuclear luminosities of 100 3CR radio galaxies with z < 0.3, bymodeling and subtracting the extended emission from the host galaxy. Weperformed a multiwavelength statistical analysis (including optical andradio data) of the properties of the nuclei following classification ofthe objects into FR I and FR II, and low-ionization galaxies (LIGs),high-ionization galaxies (HIGs), and broad-line objects (BLOs) using theradio morphology and optical spectra, respectively. The correlationsamong near-infrared, optical, and radio nuclear luminosity support theidea that the near-infrared nuclear emission of FR Is has a non-thermalorigin. Despite the difference in radio morphology, the multiwavelengthproperties of FR II LIG nuclei are statistically indistinguishable fromthose of FR Is, an indication of a common structure of the centralengine. All BLOs show an unresolved near-infrared nucleus and a largenear-infrared excess with respect to FR II LIGs and FR Is of equal radiocore luminosity. This requires the presence of an additional (anddominant) component other than the non-thermal light. Considering theshape of their spectral energy distribution, we ascribe the origin oftheir near-infrared light to hot circumnuclear dust. A near-infraredexcess is also found in HIGs, but their nuclei are substantially fainterthan those of BLO. This result indicates that substantial obscurationalong the line of sight to the nuclei is still present at 1.6 ?m.Nonetheless, HIG nuclei cannot simply be explained in terms of dustobscuration: a significant contribution from light reflected in acircumnuclear scattering region is needed to account for theirmultiwavelength properties.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, Inc.
| The Mid-infrared High-ionization Lines from Active Galactic Nuclei and Star-forming Galaxies
We used Spitzer/Infrared Spectrograph spectroscopic data on 426 galaxiesincluding quasars, Seyferts, LINERs, and H II galaxies to investigatethe relationship among the mid-IR emission lines. There is a tightlinear correlation between the [Ne V]14.3 μm and 24.3 μm (97.1 eV)and the [O IV]25.9 μm (54.9 eV) high-ionization emission lines. Thecorrelation also holds for these high-ionization emission lines and the[Ne III]15.56 μm (41 eV) emission line, although only for activegalaxies. We used these correlations to calculate the [Ne III] excessdue to star formation in Seyfert galaxies. We also estimated the [O IV]luminosity due to star formation in active galaxies and determined thatit dominates the [O IV] emission only if the contribution of the activenucleus to the total luminosity is below 5%. We find that the activegalactic nucleus dominates the [O IV] emission in most Seyfert galaxies,whereas star formation adequately explains the observed [O IV] emissionin optically classified H II galaxies. Finally, we computedphotoionization models to determine the physical conditions of thenarrow-line region where these high-ionization lines originate. Theestimated ionization parameter range is -2.8 < log U < -2.5 andthe total hydrogen column density range is 20 < log n H(cm-2) < 21.This work is based on observations made with the Spitzer SpaceTelescope, which is operated by the Jet Propulsion Laboratory,California Institute of Technology, under NASA contract 1407.
| Mapping the ionised gas around the luminous QSO HE 1029-1401: evidence for minor merger events?
We present VIMOS integral field spectroscopy of the brightestradio-quiet QSO on the southern sky HE 1029-1401 at a redshift of z =0.086. Standard decomposition techniques for broad-band imaging areextended to integral field data in order to deblend the QSO and hostemission. We perform a tentative analysis of the stellar continuum,finding a young stellar population (<100 Myr) or a featurelesscontinuum embedded in an old stellar population (10 Gyr) typical for amassive elliptical galaxy. The stellar velocity dispersion ofσ* = 320±90 km s-1 and theestimated black hole mass log(MBH/M⊙) =8.7±0.3 are consistent with the localMBH-σ* relation within theerrors. For the first time, we map the two-dimensional ionised gasdistribution and the gas velocity field around HE 1029-1401. While thestellar host morphology is purely elliptical, we find a highlystructured distribution of ionised gas out to 16 kpc from the QSO. Thegas is highly ionised solely by the QSO radiation and has asignificantly lower metallicity than would be expected for the stellarmass of the host, indicating an external origin of the gas most likelydue to minor mergers. We find a rotating gas disc around the QSO and adispersion-dominated non-rotating gas component within the central 3kpc. At larger distances the velocity field is heavily disturbed, whichcould be interpreted as another signature of past minor merger events.Alternatively, the arc-like structure seen in the ionised gas might alsobe indicative of a large-scale expanding bubble, centred on and possiblydriven by the active nucleus.Based on observations made with VIMOS integral field spectrographmounted on the Melipal VLT telescope at ESO-Paranal Observatory(programme 072.B-0550A; PI: K. Jahnke).
| A catalogue of quasars and active nuclei: 13th edition
Aims: This catalogue is aimed at presenting a compilation of allknown AGN in a compact and convenient form, and we hope that it will beuseful to all workers in this field. Methods: Like the twelfthedition, it includes position and redshift, as well as photometry (U, B,V) and 6 cm and 20 cm flux densities, when available. Results:The present version contains 133 336 quasars, 1 374 BL Lac objects, and34 231 active galaxies (including 16 517 Seyfert 1s), almost doublingthe number listed in the 12th edition. We also give a list of all knownlensed and double quasars.The catalogue (Table_QSO, Table_BL, Table_AGN and Table_reject) and thelist of references are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/518/A10or at the Observatoire de Haute Provence (http://www.obs-hp.fr/catalogues/veron213/veron213.html).
| The Discovery of Host Galaxy H I Absorption in CTA 21
We report the discovery of H I 21 cm absorption toward the well-studiedGigahertz peaked spectrum source CTA 21 (4C 16.09) using the Arecibotelescope on 2009 September 20 and 21. Recently, the frequency bandbetween 700 and 800 MHz was temporarily opened up to radio astronomywhen US TV stations were mandated to switch from analog to digitaltransmissions, with new frequency allocations. The redshifted H Ifrequency for CTA 21 falls within this band. CTA 21 has a complex radiostructure on a range of scales. The innermost prominent components areseparated by ~12 mas while weak diffuse emission extends for up to ~300mas. The H I absorption profile that we find has two main components,one narrow and the other wider and blueshifted. The total H I columndensity is 7.9 × 1020 cm-2, assuming acovering factor of unity and a spin temperature of 100 K. This H Iabsorption confirms the recently determined optical redshift of thisfaint galaxy of z ~ 0.907. We discuss this new detection in light of H Iabsorption studies toward compact radio sources, and also thepossibility that CTA 21 may be exhibiting multiple cycles of nuclearactivity. This new detection in CTA 21 is consistent with a strong trendfor detection of H I absorption in radio galaxies with evidence ofepisodic nuclear/jet activity.
| Scattered X-rays in Obscured Active Galactic Nuclei and Their Implications for Geometrical Structure and Evolution
We construct a new sample of 32 obscured active galactic nuclei (AGNs)selected from the Second XMM-Newton Serendipitous Source Catalogue toinvestigate their multiwavelength properties in relation to the"scattering fraction," the ratio of the soft X-ray flux to theabsorption-corrected direct emission. The sample covers a broad range ofthe scattering fraction (~0.1%-10%). A quarter of the 32 AGNs have avery low scattering fraction (<= 0.5%), which suggests that they areburied in a geometrically thick torus with a very small opening angle.We investigate correlations between the scattering fraction andmultiwavelength properties. We find that AGNs with a small scatteringfraction tend to have low [O III]?5007/X-ray luminosity ratios.This result agrees with the expectation that the extent of thenarrow-line region is small because of the small opening angle of thetorus. There is no significant correlation between scattering fractionand far-infrared luminosity. This implies that a scale height of thetorus is not primarily determined by starburst activity. We also comparescattering fraction with black hole mass or Eddington ratio and find aweak anti-correlation between the Eddington ratio and scatteringfraction. This implies that more rapidly growing supermassive blackholes tend to have thicker tori.
| An optical spectroscopic survey of the 3CR sample of radio galaxies with z < 0.3 . II. Spectroscopic classes and accretion modes in radio-loud AGN
In a previous paper we presented a homogeneous and 92% complete opticalspectral dataset of the 3CR radio sources with redshift <0.3. Here weuse the emission line measurements to explore the spectroscopicproperties of the sample. The 3CR sources show a bimodal distribution ofexcitation index, a new spectroscopic indicator that measures therelative intensity of low and high excitation lines. This unveils thepresence of two main sub-populations of radio-loud AGN to which we referto, following previous studies, as high and low excitation galaxies (HEGand LEG, respectively). In addition to the two main classes, we find onesource with a spectrum typical of star forming galaxies, and 3 objectsof extremely low level of excitation. All broad-line objects are HEGfrom the point of view of their narrow emission line ratios and all HEGare FR II radio-galaxies with log L178 [erg s-1]⪆ 32.8. Conversely LEG cover the whole range of radio powerencompassed by this 3CR subsample (30.7 ⪉ log L178 ⪉35.4) and they are of both FR I and FR II type. The brightest LEG areall FR II. HEG and LEG obey to two (quasi) linear correlations betweenthe optical line and extended radio luminosities, with HEG beingbrighter than LEG in the [O III] line by a factor of ~10. HEG and LEGare offset also in a plane that compares the black hole mass and theionizing nuclear luminosity. However, although HEG are associated withhigher nuclear luminosities, we find LEG among the brightest radiosources of the sample and with a clear FR II morphology,indistinguishable from those seen in HEG. This suggests that LEG are notsimply objects with a lower level of accretion. We speculate that thedifferences between LEG and HEG are related to a different mode ofaccretion: LEG are powered by hot gas, while HEG require the presence ofcold accreting material. The high temperature of the accreting gas inLEG accounts for the lack of “cold” structures (i.e.molecular torus and broad line region), for the reduced radiative outputof the accretion disk, and for the lower gas excitation.Based on observations made with the Italian Telescopio Nazionale Galileooperated on the island of La Palma by the Centro Galileo Galilei of INAF(Istituto Nazionale di Astrofisica) at the Spanish Observatorio delRoque del los Muchachos of the Instituto de Astrofísica deCanarias.
| FR II Quasars: Infrared Properties, Star Formation Rates, and Extended Ionized Gas
We present Spitzer Infrared Spectrograph spectra and Multiband ImagingPhotometer for Spitzer photometry of 12 radio-loud QSOs with FR IImorphologies at z ~ 0.3. Six of the sources are surrounded by luminousextended emission-line regions (EELRs), while the other six do not havesuch extended nebulae. The two subsamples are indistinguishable in theirmid-infrared (MIR) spectra and overall IR spectral energy distributions(SEDs). For both subsamples, the MIR aromatic features are undetected ineither individual sources or their stacked spectra, and the SEDs areconsistent with pure quasar emission without significant star formation.The upper limits to the star formation rate (SFR) are sufficiently lowthat starburst-driven superwinds can be ruled out as a mechanism forproducing the EELRs, which are instead likely the result of the ejectionof most of the gas from the system by blast waves accompanying thelaunching of the radio jets. The FR II quasars deviatesystematically from the correlation between host galaxy SFR and blackhole accretion rate apparently followed by radio-quiet QSOs, implyinglittle or no bulge growth coeval with the current intensive black holegrowth. We also present a new Spitzer estimate of the SFR for thestarburst in the host galaxy of the compact steep-spectrum radio quasar3C 48.
| The Genesis of Morphologies in Extended Radio Sources: X-Shapes, Off-Axis Distortions, and Giant Radio Sources
We examine relationships between the morphology in double radio sourcesand the radio-optical position angle offset—the relativeorientation of the radio axis with respect to the major axis of the hostgalaxy. The study was done for a representative sample of radio sources,the nearby (redshift z < 0.5) 3CRR sources, and separately forsamples of giant radio sources and X-shaped radio sources. We find thatradio morphological features have a dependence on the radio-opticalposition angle offset and on whether the source is a major- orminor-axis source. The evidence indicates an anisotropic gasenvironment, related to the ellipticity of the host galaxy, that causesthe source linear size evolution, strength of backflow in the radiolobes, off-axis lobe distortions and the formation of wings, andX-shaped radio sources to depend on the radio-optical position angleoffset. We identify a class of X-shaped radio sources, which are eitheredge-darkened or lacking hotspots, and appear to have inner doublessuggesting a restarting of activity. We suggest a common formationmechanism, requiring backflows, for these apparently FR-I X-shaped radiosources as well as the edge-brightened X-shaped sources.
| An optical spectroscopic survey of the 3CR sample of radio galaxies with z < 0.3. I. Presentation of the data
We present a homogeneous and 92% complete dataset of optical nuclearspectra for the 113 3CR radio sources with redshifts <0.3, obtainedwith the Telescopio Nazionale Galileo. For these sources we could obtainuniform and uninterrupted coverage of the key spectroscopic opticaldiagnostics. The observed sample, including powerful classical FR IIradio-galaxies and FR I, together spanning four orders of magnitude inradio-luminosity, provides a broad representation of the spectroscopicproperties of radio galaxies. In this first paper we present an atlas ofthe spectra obtained, provide measurements of the diagnostic emissionline ratios, and identify active nuclei with broad line emission. Thesedata will be used in follow-up papers to address the connection betweenthe optical spectral characteristics and the multiwavelength propertiesof the sample.Based on observations made with the Italian Telescopio Nazionale Galileooperated on the island of La Palma by the Centro Galileo Galilei of INAF(Istituto Nazionale di Astrofisica) at the Spanish Observatorio delRoque del los Muchachos of the Instituto de Astrofisica de Canarias.
| Extended Emission-Line Regions: Remnants of Quasar Superwinds?
We give an overview of our recent integral-field-unit spectroscopy ofluminous extended emission-line regions (EELRs) around low-redshiftquasars, including new observations of five fields. Previous work hasshown that the most luminous EELRs are found almost exclusively aroundsteep-spectrum radio-loud quasars, with apparently disordered globalvelocity fields, and little, if any, morphological correlation witheither the host galaxy or the radio structure. Our new observationsconfirm and expand these results. The EELRs often show some clouds withvelocities exceeding 500 km s-1, ranging up to 1100 kms-1, but the velocity dispersions, with few exceptions, arein the 30-100 km s-1 range. Emission-line ratios show thatthe EELRs are clearly photoionized by the quasars. Masses of the EELRsrange up to 1010Msun. Essentially all of the EELRsshow relatively low metallicities, and they are associated with quasarsthat, in contrast to most, show similarly low metallicities in theirbroad-line regions. The two objects in our sample that do not haveclassical double-lobed radio morphologies (3C 48, with acompact-steep-spectrum source; Mrk 1014, radio quiet, but with a weakcompact-steep-spectrum source) are the only ones that appear to haverecent star formation. While some of the less luminous EELRs may haveother origins, the most likely explanation for those in our sample isthat they are examples of gas swept out of the host galaxy by alarge-solid-angle blast wave accompanying the production of the radiojets. The triggering of the quasar activity is almost certainly theresult of the merger of a gas-rich galaxy with a massive, gas-poorgalaxy hosting the supermassive black hole.Based in part on observations obtained at the Gemini Observatory, whichis operated by the Association of Universities for Research inAstronomy, Inc., under a cooperative agreement with the NSF on behalf ofthe Gemini partnership: the National Science Foundation (United States),the Particle Physics and Astronomy Research Council (United Kingdom),the National Research Council (Canada), CONICYT (Chile), the AustralianResearch Council (Australia), CNPq (Brazil), and CONICET (Argentina).Gemini Program ID: GN-2007A-Q-43 and GN-2007B-Q-12.
| The Fate of Young Radio Galaxies: Decelerations Inside Host Galaxies?
We examine the evolution of variously sized radio galaxies (i.e.,compact symmetric objects [CSOs], medium-size symmetric objects [MSOs],Fanaroff-Riley type II (FR II) radio galaxies by comparing the relationbetween the hot spot size and the projected linear size with acoevolution model of hot spots and a cocoon. We take account of thedeceleration effect by the cocoon head growth. We find that the advancespeed of hot spots and lobes inevitably show the deceleration phase(CSO-MSO phase) and the acceleration phase (MSO-FR II phase). This isascribed to the change of the power-law index of ambient density profilein the MSO phase (~1 kpc). It is also found that the cocoon shapebecomes nearly spherical or disrupted for MSOs, while an elongatedmorphology is predicted for CSOs and FR II galaxies. This seems to beconsistent with the higher fraction of distorted morphology of MSOs thanthat of CSOs and FR II galaxies. Finally, we predict that only CSOswhose initial advance speed is higher than about 0.1 c can evolve intoFR II galaxies, comparing the hot spot speed with the sound speed of theambient medium.
| Observed properties of FRII quasars and radio galaxies at z < 1.0
In a long-term observing project we have imaged a complete sample ofFanaroff-Riley II (FRII) quasars and radio galaxies with z < 1.0 athigh resolution and high sensitivity with the Very Large Array (VLA) andMulti-Element Radio-Linked Interferometer (MERLIN). This sample of 98sources includes 15 quasars, 11 broad-line radio galaxies and 57narrow-line radio galaxies, allowing unification to be considered interms of source morphological properties. Radio maps of all the targetshave been presented in earlier papers. Here we carry out a systematicanalysis of the properties of the jets, cores, lobes and hotspots ofobjects in the sample. The majority of the tests that we perform showthat the data are consistent with a model in which quasars andbroad-line radio galaxies are unified with narrow-line objects.Relativistic beaming is the main effect that determines the propertiesof kiloparsec-scale jets, and it may also have some effect on hotspots.However, some properties of the sample are difficult to account for insimple unified models.
| Hubble Space Telescope Near-infrared Snapshot Survey of 3CR Radio Source Counterparts. II. An Atlas and Inventory of the Host Galaxies, Mergers, and Companions
We present the second part of an H-band (1.6 μm) ``atlas'' ofz<0.3 3CR radio galaxies, using the Hubble Space Telescope NearInfrared Camera and Multi-Object Spectrometer (HST NICMOS2). We presentnew imaging for 21 recently acquired sources and host galaxy modelingfor the full sample of 101 (including 11 archival)-an 87% completionrate. Two different modeling techniques are applied, following thoseadopted by the galaxy morphology and the quasar host galaxy communities.Results are compared and found to be in excellent agreement, althoughthe former breaks down in the case of sources with strong activegalactic nuclei (AGNs). Companion sources are tabulated, and thepresence of mergers, tidal features, dust disks, and jets are cataloged.The tables form a catalog for those interested in the structural andmorphological dust-free host galaxy properties of the 3CR sample, andfor comparison with morphological studies of quiescent galaxies andquasar host galaxies. Host galaxy masses are estimated and found totypically lie at around 2×1011 Msolar. Ingeneral, the population is found to be consistent with the localpopulation of quiescent elliptical galaxies, but with a longer tail tolow Sérsic index, mainly consisting of low-redshift (z<0.1)and low-radio-power (FR I) sources. A few unusually disky FR II hostgalaxies are picked out for further discussion. Nearby external sourcesare identified in the majority of our images, many of which we argue arelikely to be companion galaxies or merger remnants. The reduced NICMOSdata are now publicly available from our Web site.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. (AURA),under NASA contract NAS5-26555.
| New Indicators for AGN Power: The Correlation between [O IV] 25.89 μm and Hard X-Ray Luminosity for Nearby Seyfert Galaxies
We have studied the relationship between the [O IV] 25.89 μmemission-line luminosities, obtained from Spitzer spectra, the X-raycontinua in the 2-10 keV band, primarily from ASCA, and the 14-195 keVband obtained with the SWIFT Burst Alert Telescope (BAT), for a sampleof nearby (z<0.08) Seyfert galaxies. For comparison, we have examinedthe relationship between the [O III] λ5007, the 2-10 keV, and the14-195 keV luminosities for the same set of objects. We find that boththe [O IV] and [O III] luminosities are well correlated with the BATluminosities. When comparing [O IV] and [O III] luminosities for thedifferent types of galaxies, we find that the Seyfert 2s havesignificantly lower [O III] to [O IV] ratios than the Seyfert 1s. Wesuggest that this is due to more reddening of the narrow-line region(NLR) of the Seyfert 2s, since the [O IV] 25.89 μm emission line ismuch less affected by extinction. The combined effects of reddening andthe X-ray absorption is the probable reason why the [O III] versus 2-10keV correlation is better than the [O IV] versus 2-10 kev correlation.Based on photoionization models, we find that the [O IV] comes fromhigher ionization states and lower density regions than previous studieshad determined for [O III]. Overall, we find the [O IV] to be anaccurate indicator of the power of the AGN.
| The interaction between jets and clouds in the 3CR galaxies
From the HST/WFPC2 3CR Snapshot Survey, data taken with the filterF555W, F702W and narrow-ramp, a set of galaxies with noticeable extendedstructure were selected (e.g. 3C 79, 3C 135, 3C 234, etc). All of theseobjects show large regions of [OIII] lambda 5007Å emission (narrowramp filter) and the broad-band filters data show similar structuresindicating the presence of strong emission in several lines over theseregions. The morphology observed seems to be related (e.g. same positionangle, direct overlapping or similar shape) with the radio-jet. For somecandidates with these properties GMOS/Gemini spectroscopy was taken.These data (both HST direct imaging and Gemini spectroscopy) can betested with diagnostic diagrams and total UV photons budget tounderstand the source of energy that is ionizing the gas. This source ofionization was commonly believed to be the UV photons emitted by thepowerful active galactic nuclei (AGN), but several of these objects showclearly that shocks produced by the radio jet are the main cause of theobserved gas line emission. We show in this work, the results obtainedover some of these radio-galaxies: 3C 135, 3C 180, 3C 234 and 3C 284.
| The Host Galaxy and the Extended Emission-Line Region of the Radio Galaxy 3C 79
We present extensive ground-based spectroscopy and HST imaging of 3C 79,an FR II radio galaxy associated with a luminous extended emission-lineregion (EELR). Surface brightness modeling of an emission-line-free HSTR-band image reveals that the host galaxy is a massive elliptical with acompact companion 0.8" away and 4 mag fainter. The host galaxy spectrumis best described by an intermediate-age (1.3 Gyr) stellar population(4% by mass), superimposed on a 10 Gyr old population and a power law(αλ=-1.8) the stellar populations are consistentwith supersolar metallicities, with the best fit given by the 2.5Zsolar models. We derive a dynamical mass of4×1011 Msolar within the effective radiusfrom the velocity dispersion. The EELR spectra clearly indicate that theEELR is photoionized by the hidden central engine. Photoionizationmodeling shows evidence that the gas metallicity in both the EELR andthe nuclear narrow-line region is mildly subsolar (0.3-0.7Zsolar), significantly lower than the supersolarmetallicities deduced from typical active galactic nuclei in the SloanDigital Sky Survey. The more luminous filaments in the EELR exhibit avelocity field consistent with a common disk rotation. Fainter clouds,however, show high approaching velocities that are uncoupled from thisapparent disk rotation. The striking similarities between this EELR andthe EELRs around steep-spectrum radio-loud quasars provide furtherevidence for the orientation-dependent unification schemes. Themetal-poor gas is almost certainly not native to the massive hostgalaxy. We suggest that the close companion galaxy could be the tidallystripped bulge of a late-type galaxy that is merging with the hostgalaxy. The interstellar medium of such a galaxy is probably the sourcefor the low-metallicity gas in 3C 79.Based in part on observations obtained at the Gemini Observatory, whichis operated by the Association of Universities for Research inAstronomy, Inc., under a cooperative agreement with the NSF on behalf ofthe Gemini partnership: the National Science Foundation (United States),the Particle Physics and Astronomy Research Council (United Kingdom),the National Research Council (Canada), CONICYT (Chile), the AustralianResearch Council (Australia), CNPq (Brazil) and CONICET (Argentina).Gemini Program ID: GN-2006B-C-3. Some of the data presented herein wereobtained at the W. M. Keck Observatory, which is operated as ascientific partnership among the California Institute of Technology, theUniversity of California and the National Aeronautics and SpaceAdministration. The Observatory was made possible by the generousfinancial support of the W. M. Keck Foundation. Based also in part onobservations made with the NASA/ESA Hubble Space Telescope, obtainedfrom the Data Archive at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555.
| Radio Frequency Spectra of 388 Bright 74 MHz Sources
As a service to the community, we have compiled radio frequency spectrafrom the literature for all sources within the VLA Low Frequency SkySurvey (VLSS) that are brighter than 15 Jy at 74 MHz. Over 160references were used to maximize the amount of spectral data used in thecompilation of the spectra, while also taking care to determine thecorrections needed to put the flux densities from all reference on thesame absolute flux density scale. With the new VLSS data, we are able tovastly improve on previous efforts to compile spectra of bright radiosources to frequencies below 100 MHz because (1) the VLSS flux densitiesare more reliable than those from some previous low-frequency surveysand (2) the VLSS covers a much larger area of the sky(?>-30deg) than many other low-frequency surveys(e.g., the 8C survey). In this paper, we discuss how the spectra wereconstructed and how parameters quantifying the shapes of the spectrawere derived. Both the spectra and the shape parameters are madeavailable here to assist in the calibration of observations made withcurrent and future low-frequency radio facilities.
| Evidence of a type 1/type 2 dichotomy in the correlation between quasar optical polarization and host-galaxy/extended emission position angles
Aims.For Seyfert galaxies, the AGN unification model provides a simpleand well-established explanation of the type 1/type 2 dichotomy throughorientation-based effects. The generalization of this unification modelto the higher luminosity AGNs that quasars are remains a key question.The recent detection of type 2 radio-quiet quasars seems to support suchan extension. We propose a further test of this scenario. Methods: Onthe basis of a compilation of quasar host-galaxy position anglesconsisting of previously published data and of new measurementsperformed using HST Archive images, we investigate the possibleexistence of a correlation between the linear polarization positionangle and the host-galaxy/extended emission position angle of quasars. Results: We find that the orientation of the rest-frame UV/blue extendedemission is correlated to the direction of the quasar polarization. Fortype 1 quasars, the polarization is aligned with the extended UV/blueemission, while these two quantities are perpendicular in type 2objects. This result is independent of the quasar radio loudness. Weinterpret this (anti-)alignment effect in terms of scattering in atwo-component polar+equatorial model that applies to both type 1 andtype 2 objects. Moreover, the orientation of the polarization -and thenof the UV/blue scattered light- does not appear correlated to the majoraxis of the stellar component of the host-galaxy measured from near-IRimages.
| A Study of 13 Powerful Classical Double Radio Galaxies
We have carried out an extensive study of a sample of 13 large, powerfulFanaroff-Riley type II radio galaxies with the Very Large Array inmultiple configurations at 330 MHz and 1.4, 5, and 8 GHz. We present thetotal intensity, polarization, spectral index, and rotation measure mapsof the sources. On the whole, the 13 FR II sources have symmetricstructures with arm-length ratios close to unity, small misalignmentangles, and low values of radio core prominence, suggesting that theseradio galaxies lie close to the plane of the sky. We have revisited somewell-known radio galaxy correlations using a large combined data setcomprising our radio galaxies and others from the literature. We confirmthat the hot spot size correlates with the core-hot spot distance. Thehot spot spectral index is correlated with and flatter than the lobespectral index, consistent with the assumptions of spectral agingmodels. Both the hot spot and lobe spectral index are correlated withredshift. The depolarization asymmetry in the lobes is not correlatedwith the radio core prominence or misalignment angle, which arestatistical indicators of orientation. The ``Liu-Pooley'' correlation oflobe depolarization with the lobe spectral index is significant in ourradio galaxy sample. Furthermore, the lobe with the steeper spectralindex and greater depolarization is shorter and fatter. The arm-lengthratio seems to be correlated with the misalignment angle between the twosides of the radio source and strongly anticorrelated with the axialratio, consistent with environmental effects and/or a change in theoutflow direction. In this sample, asymmetries in the local environmentsand/or motion of the outflow axis are likely to be more important thanrelativistic beaming effects.
| Aromatic Features in AGNs: Star-forming Infrared Luminosity Function of AGN Host Galaxies
We describe observations of aromatic features at 7.7 and 11.3 μm inAGNs of three types, including PG, 2MASS, and 3CR objects. The featurehas been demonstrated to originate predominantly from star formation.Based on the aromatic-derived star-forming luminosity, we find that thefar-IR emission of AGNs can be dominated by either star formation ornuclear emission; the average contribution from star formation is around25% at 70 and 160 μm. The star-forming infrared luminosity functionsof the three types of AGNs are flatter than those of field galaxies,implying that nuclear activity and star formation tend to be enhancedtogether. The star-forming luminosity function is also a function of thestrength of nuclear activity from normal galaxies to the bright quasars,with luminosity functions becoming flatter for more intense nuclearactivity. Different types of AGNs show different distributions in thelevel of star formation activity, with 2MASS > PG > 3CR starformation rates.
| Bulges and Disklike Components in the Host Galaxies of Low-Redshift 3CR Sources: A Near-Infrared View of Their Radial Brightness Profiles
We analyze the near-infrared luminosity profiles and photometricparameters of the host galaxies of 3CR radio sources with z<0.3, toinvestigate their physical nature. Our sample includes 82 galaxies, ofwhich 22 (27%) are FR Is and 60 (73%) are FR IIs. Using near-infrareddata taken both with NICMOS on board the Hubble Space Telescope and fromthe ground with the Telescopio Nazionale Galileo, we find thatluminosity profiles are very well described by a single Sérsiclaw in 52% of the cases and that for the remaining objects (48%) it isnecessary to include an exponential profile, which indicates thepresence of a second disklike component. The average bulge-to-disklikecomponents luminosity ratio for the galaxies is (b/e)~1.1. The analysisof the photometric parameters of the subsamples indicates that FR Is andFR IIs show rather similar bulges in terms of effective surfacemagnitude, effective radius, and Sérsic index. On the other hand,the disklike components in FR I and FR II hosts show, on average,different properties. Central surface magnitudes are dimmer and scalelengths are greater by a factor of 2 in FR Is when compared to FR IIs.We also estimate the black hole mass associated with each galaxy usingtwo different methods that claim tight correlations of the black holemass (MBH) with the infrared bulge luminosity(Lbulge) and with the Sérsic index (n). Our dataindicate that masses obtained through these two methods show a highdispersion and that MBH obtained through Lbulgeare systematically higher (by a factor of ~3) than those obtained usingn. This result may reflect the fact that for our sample galaxies we donot find any correlation between Lbulge and n.Based on observations made with the NASA/ESA Hubble Space Telescope(HST), obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS5-26555.
| Isophotal Structure and Dust Distribution in Radio-loud Elliptical Galaxies
We investigate isophotal properties and dust morphology in the nuclearregions of 84 radio galaxies, imaged in the optical and near-infrared aspart of Hubble Space Telescope snapshot surveys. We present asample-wide trend between host galaxy isophotal structure and theinclination of dusty circumnuclear disks at the centers of 13 of theseobjects. We find that galaxies containing edge-on disks are invariablyseen to possess boxy isophotes, while round, face-on disks are seenexclusively in objects with round or elliptical isophotes. Dust-richsources with disky isophotes are observed only to possess dust in theform of extended filamentary lanes, and not in settled distributionslike disks. As we do not expect that edge-on and face-on disks reside indifferent populations of galaxies, we conclude that perceived isophotalboxiness is dependent on the angle at which the observer views the hostgalaxy's axis of symmetry. We discuss our results in the context ofdissipative merger scenarios, and infer that dusty disks primarilyreside in old, boxy remnants of gas-poor galaxy mergers, whereasfilamentary dust lanes reside in younger disky remnants of gas-richmergers.
| Giant Lyα nebulae around z > 2 radio galaxies: evidence for infall
We present an investigation into the possible relationship betweenside-to-side asymmetries of powerful radio galaxies at high redshift,with the goal of understanding the geometry, orientation and gasdynamics of these sources. Our sample consists of 11 radio galaxies at2.3 <= z <= 3.6 previously known to have giant, kinematicallyquiescent nebulae. We identify several correlated asymmetries: on theside of the brightest radio jet and hotspot (i) the redshift of thekinematically quiescent nebula is highest, (ii) Lyα is brighterrelative to the other lines and continuum, (iii) the radio spectrum isflattest and (iv) the radio structure has its highest polarization.These asymmetries are not found to be correlated with either the radioarm length asymmetry or the brightness asymmetry of the UV-opticalemitting material. The correlation between the radio brightnessasymmetry and the radial velocity of the quiescent gas also appears tobe present in powerful radio galaxies with 0 <~ z <~ 1.Collectively, these asymmetries are most naturally explained as aneffect of orientation, with the quiescent nebulae in infall: this is thefirst study to distinguish between the rotation, infall, outflow andchaotic motion scenarios for the kinematically quiescent emission-linenebulae around powerful active galactic nuclei.
| A Relation between the Mid-Infrared [Ne V] 14.3 μm and [Ne III] 15.6 μm Lines in Active Galactic Nuclei
We present a strong correlation between the [Ne V] 14.3 μm and [NeIII] 15.6 μm emission lines arising from the narrow-line regions(NLRs) of active galactic nuclei (AGNs), spanning 4 orders of magnitudein luminosity. The data are compiled primarily from Spitzer SpaceTelescope observations of nearby Seyfert galaxies (median z=0.01) and 3Cradio sources (median z=0.52). This correlation is consistent withearlier studies in the optical/UV bands showing that line ratios arisingin the NLRs are remarkably constant across AGNs. We also show that thecorrelation allows only a very narrow range in ionization parameter forsimple photoionization models. The observed correlation will place tightconstraints on alternative models, which predict constant line ratiosover a broader range in ionization parameter.
| Unveiling hidden AGN by IR observations
AGN can be dust-hidden by two ways and this talk considers how to unveilthem in the infrared: firstly, the powerful 3CR radio galaxies, i.e.,type-2 AGN which suffer from anisotropic obscuration of the nuclearregion by the dust torus, and secondly, type-1 quasars, which seem to beisotropically reddened by dust, so that they escape detection viaoptical-UV colour criteria.Using Spitzer MIR spectroscopy we show thatthe powerful 3CR radio galaxies have similar high excitation lines, forinstance, [Ne V]λ14.3 μm, as quasars matched in radio powerand redshift. This solves the long debate about the apparent differenceof quasars and radio galaxies in favor of the orientation-dependentunified scheme.Combining the ISOCAM Parallel Mode Survey at 6.7 μm(LW2 filter) with the Two Micron All Sky Survey we used moderate colourcriteria H ‑ K > 0.5 and K ‑ LW2 > 2.7 to search forAGN independent of dust extinction. With a surface density of about 2deg‑2 down to R < 18 mag the ISO-2MASS type-1 QSOsoutnumber the 1.35 deg‑2 of the SDSS DR3 quasar surveyby 50%. About one third of the ISO-2MASS QSOs show very red star-likeoptical colours.
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