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Radio Continuum Jet in NGC 7479
The barred galaxy NGC 7479 hosts a remarkable jetlike radio continuumfeature: bright, 12 kpc long in projection, and hosting an alignedmagnetic field. The degree of polarization is 6%-8% along the jet andremarkably constant, which is consistent with helical field models. Theradio brightness of the jet suggests strong interaction with the ISM andhence a location near the disk plane. We observed NGC 7479 at fourwavelengths with the VLA and Effelsberg radio telescopes. Theequipartition strength is 35-40 μG for the total and >=10 μGfor the ordered magnetic field in the jet. The jet acts as a bright,polarized background. Faraday rotation between 3.5 and 6 cm anddepolarization between 6 and 22 cm can be explained by magnetoionic gasin front of the jet, with thermal electron densities of ~=0.06cm-3 in the bar and ~=0.03 cm-3 outside the bar.The regular magnetic field along the bar points toward the nucleus onboth sides. The regular field in the disk reveals multiple reversals,probably consisting of field loops stretched by a shearing gas flow inthe bar. The projection of the jet bending in the sky plane is in thesense opposite to that of the underlying stellar and gaseous spiralstructure. The bending in 3D is most easily explained as a precessingjet, with an age less than 106 yr. Our observations areconsistent with very recent triggering, possibly by a minor merger. NGC7479 provides a unique opportunity to study interaction-triggered 15 kpcscale radio jets within a spiral galaxy.
| The Westerbork SINGS survey. I. Overview and image atlas
We have obtained moderately deep radio continuum imaging at 18 and 22 cmwith the Westerbork array of 34 nearby galaxies drawn from the SpitzerSINGS and Starburst samples to enable complimentary analysis. Thesub-sample have an optical major axis diameter in excess of 5 arcmin andare North of Declination 12.5°. Sub-sample galaxies span a very widerange of morphological types and star formation rates. Resolveddetection was possible for every galaxy. This constitutes a first timedetection at GHz radio frequencies for about half of the sample.Analysis of both total intensity and polarization properties of thesample will be published in companion papers. Both the HI and OHmain-lines of the target galaxies were within the observed band-pass,albeit with only coarse velocity resolution. Only two low masselliptical galaxies were undetected in HI. Four of the sub-samplegalaxies were detected in OH main-line absorption, including two newdetections. The results are presented in the form of an image atlas forwhich a standard transfer function and image size are used throughoutand whereby the radio continuum, DSS optical and integrated HI aredisplayed side-by-side. Continuum and HI line photometry are tabulatedfor all targets.
| 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).
| A catalogue of quasars and active nuclei: 12th edition
Aims.This catalogue is aimed at presenting a compilation of all knownAGN in a compact and convenient form and we hope that it will be usefulto all workers in this field.Methods.Like the eleventh edition, itincludes position and redshift as well as photometry (U, B, V) and 6 cmflux densities when available. We now give 20 cm rather than 11 cm fluxdensities.Results.The present version contains 85 221 quasars,1122 BL Lac objects and 21 737 active galaxies (including 9628 Seyfert1s), almost doubling the number listed in the 11th edition. We also givea list of all known lensed and double quasars.
| The host galaxy/AGN connection in nearby early-type galaxies. A new view of the origin of the radio-quiet/radio-loud dichotomy?
This is the third in a series of three papers exploring the connectionbetween the multiwavelength properties of AGN in nearby early-typegalaxies and the characteristics of their hosts. Starting from aninitial sample of 332 galaxies, we selected 116 AGN candidates requiringthe detection of a radio source with a flux limit of ~1 mJy, as measuredfrom 5 GHz VLA observations. In Paper I we classified the objects withavailable archival HST images into "core" and "power-law" galaxies,discriminating on the basis of the nuclear slope of their brightnessprofiles. We used HST and Chandra data to isolate the nuclear emissionof these galaxies in the optical and X-ray bands, thus enabling us (oncecombined with the radio data) to study the multiwavelength behaviour oftheir nuclei. The properties of the nuclei hosted by the 29 coregalaxies were presented in Paper II Core galaxies invariably host aradio-loud nucleus, with a median radio-loudness of Log R = 3.6 and anX-ray based radio-loudness parameter of Log RX = -1.3. Herewe discuss the properties of the nuclei of the 22 "power-law" galaxies.They show a substantial excess of optical and X-ray emission withrespect to core galaxies at the same level of radio luminosity.Conversely, their radio-loudness parameters, Log R 1.6 and LogRX -3.3, are similar to those measured in Seyfertgalaxies. Thus the radio-loudness of AGN hosted by early-type galaxiesappears to be univocally related to the host's brightness profile:radio-loud AGN are only hosted by core galaxies, while radio-quiet AGNare found only in power-law galaxies. The brightness profile isdetermined by the galaxy's evolution, through its merger history; ourresults suggest that the same process sets the AGN flavour. In thisscenario, the black holes hosted by the merging galaxies rapidly sinktoward the centre of the newly formed object, setting its nuclearconfiguration, described by e.g. the total mass, spin, mass ratio, orseparation of the SMBHs. These parameters are most likely at the originof the different levels of the AGN radio-loudness. This connection mightopen a new path toward understanding the origin of theradio-loud/radio-quiet AGN dichotomy and provide us with a further toolfor exploring the co-evolution of galaxies and supermassive black holes.
| VLA High-Resolution 1.4 and 8.4 GHz Mapping of the Barred Galaxy NGC 3367
We report new radio continuum observations with an angular resolution of2.1" at 1.4 GHz (20 cm) and 0.28" at 8.4 GHz (3.6 cm) of the barredgalaxy NGC 3367. In the map at 1.4 GHz, the central nuclear regionconnects to the southwest lobe, with a projected structure at a positionangle (P.A.) of ~230°, forming a jetlike structure. The map at 8.4GHz shows a compact unresolved source (smaller than 65 pc in diameter)associated with emission from the nucleus and several compact sourceslocated within a radius of about 300 pc, forming a circumnuclearstructure. The compact core, jet, and lobes form a small, low-powercounterpart to radio galaxies, with a flow axis that is out of the planeof the galaxy. The flow axis (P.A.~230deg) coincides with theP.A. of the major axis of the galaxy and is thus inclined to therotation axis of the disk. In addition, the flow axis differs by about20° from the major axis of the stellar bar. Assuming that thestellar bar rotates counterclockwise (i.e., assuming trailing spiralarms), this difference in angle is taken as an argument in favor ofhaving the jetlike structure out of the plane of the disk and notassociated with the stellar bar.
| A Large-Scale Jet and FR I Radio Source in a Spiral Galaxy: The Host Properties and External Environment
We have identified a large (~200 h-175 kpc),powerful double radio source whose host galaxy is clearly a disk andmost likely a spiral. This FR I-like radio galaxy is located very nearthe center of the richness class 0 cluster A428. The existence of suchan object violates a fundamental paradigm for radio-loud active galacticnuclei (AGNs). In our first paper, we showed that this object was mostconsistent with a spiral host classification with optical emission-lineratios and colors suggestive of an active nucleus. However, we were notable to confirm actual radio jet emission based on the maps available atthat time. In this paper, we present new, higher resolution radioimaging, a radio/millimeter continuum spectrum for the nucleus, adetection of H I absorption against the bright radio core, an upperlimit to CO emission and the gas mass, and 70 (68 new) optical redshiftsmeasured in the direction of A428. We confirm the existence of a radiojet at 20 cm, extending 42 h-175 into the southernlobe. At 3.6 cm, we also detect a nuclear jet similar in length to thatin M87, although 10 times weaker. We believe that this is the firstdetection of a radio jet on these scales in a disk/spiral host galaxy.The nuclear radio spectrum is similar to many blazar- or quasar-likeobjects, suggesting that the galaxy harbors an imbedded and obscuredAGN. We model a turnover in the spectrum at low frequencies as a resultof free-free absorption. We detect very strong and narrow H Iabsorption, with nearly the entire 20 cm continuum flux of the corebeing absorbed, implying an unusually large optical depth (τ~1). Themost consistent model is that we are viewing the nucleus through adisklike distribution of gas in the interstellar medium, possiblythrough a spiral arm or a warp to account for the above-average columndensity. From the radial velocity distribution, we find that A428 is infact made up of at least two clumps of galaxies separated by ~3300 kms-1, which themselves appear to be imbedded in a nearlycontinuous distribution of galaxies over 13,000 km s-1 invelocity space. Thus, the environment around this unusual radio sourceis more like that of a poor galaxy group imbedded in a filament-likestructure viewed end-on.
| The unusual host galaxy of the BL Lac object PKS 1413+135
The BL Lacertae object PKS 1413+135 is associated with a disc-dominatedgalaxy that heavily absorbs the BL Lac nucleus at optical and X-raywavelengths. It has been argued whether this galaxy is actually the hostgalaxy of PKS 1413+135 or whether the BL Lac is a background QSO,gravitationally lensed by the apparent host galaxy. We have obtaineddeep high-resolution H-band images of this unusual BL Lac object usingthe UKIRT IRCAM3. Our observations show that the BL Lac nucleus iscentred within <=0.05arcsec of the galaxy. Based on this result, weassess the probability for the lensing scenario and come to theconclusion that the disc galaxy is indeed the host of PKS 1413+135. Thegalaxy shows peanut-shaped isophotes, suggesting the presence of acentral bar, which is a common feature of AGN.
| An Unusual Radio Galaxy in Abell 428: A Large, Powerful FR I Source in a Disk-dominated Host
We report the discovery of a powerful (~1024 h^{-2}75{WHz}^{-1} at 20 cm) FR I radio source in a highly flatteneddisk-dominated galaxy. Half the radio flux from this source isconcentrated within the host galaxy, with the remainder in a pair ofnearly symmetrical lobes of total extent ~200 kpc nearly perpendicularto the disk. Traditional wisdom maintains that powerful, extended radiosources are found only in ellipticals or recent merger events. We reportB, R, J, and K imaging, optical spectroscopy, a rotation curve, an IRASdetection, and a VLA 20 cm image for this galaxy, 0313-192. The opticaland near-infrared images clearly show a disk. We detect apparent spiralarms in a deep B-band exposure, and a dust lane from a higher resolutionB-band image. The reddened nucleus is consistent with extinction by asimilar dust lane. The optical spectrum suggests a central AGN and showssome evidence of a starburst, with both the AGN and central starlightappearing substantially reddened (perhaps by the optical dust lane).From analysis of the extended line emission in [O III] and H alpha , wederive a rotation curve consistent with an early-type, dusty spiral seenedge-on. From the IRAS detection at 60 and 100 mu m, we find that theratio of far-infrared to radio flux places this object firmly as a radiogalaxy (i.e., the radio emission is not powered by star formation). Theradio structure suggests that the radio source in this galaxy is relatedto the same physical mechanisms that are present in jet-fed powerfulradio sources, and that such powerful, extended sources can (albeitextremely rarely) occur in a disk-dominated host.
| A 20 Centimeter VLA Survey of Abell Clusters of Galaxies. VII. Detailed Radio Images
We present detailed radio images, and models, obtained with the VeryLarge Array at 20 cm for 199 radio galaxies in Abell clusters ofgalaxies.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| A 20 CM Survey of Abell Clusters of Galaxies. V. Optical Observations and Surface Photometry
We present results from a program of optical imaging of 265 radiogalaxies in rich clusters. Using isophotal surface photometry, weinvestigate the optical properties such as the morphology, surface-brightness profiles, surface-brightness/size relationships,ellipticities, and the frequency of nonelliptical isophotes. The resultsare compared to a "normal" nonradio-selected sample of ellipticalgalaxies from the same clusters. The goal is to determine if the parentpopulation of FR I radio galaxies can be distinguished optically fromradio-quiet galaxies. The results of the analysis are that clusterellipticals are a very homogeneous class of objects. The opticalproperties are consistent with a one-parameter family, where the opticalluminosity is the fundamental parameter. In all tests considered, radio-loud FR I galaxies cannot be distinguished optically from radio-quietgalaxies selected from the same environment. The local density of nearbycompanions (<20 kpc) and the frequency of morphological peculiaritiesor tidal interactions are not statistically different between theradio-loud and quiet samples. There is some suggestion from comparisonto published samples of non-cluster radio galaxies, that the clusterenvironment is not condusive to long-lived tidal interactions, and thatsuch events may be more important to galaxy evolution in poor groups andlower density environments. Such events appear to have little influenceon the formation of FR I radio galaxies in rich clusters. The resultsare consistent with the idea that all elliptical galaxies may at sometime (or many times) contain powerful (rR I) radio sources.
| A 20 CM VLA Survey of Abell clusters of galaxies. 4: The radio sample and cluster properties
This is the fourth in a series of papers describing an in depth study ofa large statistical sample of radio galaxies in Abell clusters. Thissample forms the basis of a detailed optical and radio study of the hostgalaxy properties, environments, and evolutionary models for radiogalaxies as a class of objects. In this paper, we examine the radiodetection statistics as a function of cluster morphological type, galaxyrichness, and spatial location within the cluster distribution. Theserelationships are also parameterized as a funtion of radio power. Thespatial distributions of the radio sources as a function of distancefrom the cluster center indicate that radio galaxies are preferentiallylocated at small radii from the center of the cluster potential. This isobserved as a factor of 2-3 excess over that predicted by a King-modelsurface-density distribution. The excess is higher in the upper radiopower bin. This result is easily explained, however, from the spatialdistribution of the brightest galaxies and the relationship betweenradio and optical luminosity. The sample is divided into richnessclasses 0, 1, and 2, according to Abell's criterion. and in two radiopower ranges. While simple counting shows that richer clusters have moreradio galaxies in both radio power bins, when the detections are scaledto the number of galaxies surveyed in each cluster, no significantcorrelations are found. This result implies that the number of radiogalaxies detected simply scales with the number of galaxies surveyed.The higher galaxy density (and presumably higher ICM gas density) inricher clusters does not appear to affect the rate of radio sourceformation. The clusters are divided into Rood-Sastry and Bautz-Morganmorphological types. While it would appear that the more regularclusters have higher radio detection rates, when the classes arenormalized to the number of galaxies, the radio detection rates arefound to be identical regardless of cluster morphology. In conclusion,it is the optical properties of the host galaxy which most influenceboth the radio detection rate and the radio source properties. Thecluster properties, galaxy density, and spatial location of the galaxydo not significantly affect the observed radio statistics.
| Optical spectroscopy of radio galaxies in Abell clusters. 1: Redshifts and emission-line properties
We present results of a program of optical spectroscopy of radiogalaxies in rich clusters. Redshifts are reported for 268 radio galaxiesor close companions in Abell clusters and 36 objects which turned out tobe foreground or background objects. Absolute line strengths are alsoreported for the 3727 A (O II) line and the (N II)/H alpha complex. Wefind no evidence that the radio activity in our sample of mostly FR Iradio galaxies is associated with emission-line luminosities above thosefound in normal galaxies of the same absolute magnitude and opticaltype. We also find that the radial velocity differences between radiogalaxies and the cluster mean seem mainly to be a function of galaxyabsolute magnitude rather than radio properties.
| A 20 centimeter VLA survey of Abell clusters of galaxies. II - Images and optical identifications
Radio contour maps, models, and optical identifications for 130 radiogalaxies in Abell clusters of galaxies are presented. Results ofGaussian model fits to sources smaller than two beamwidths arepresented. The observations were made between 1979 and 1984 using theVLA at 20 cm.
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