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The Molonglo Southern 4 Jy Sample (MS4). II. ATCA Imaging and Optical Identification
Of the 228 sources in the Molonglo Southern 4 Jy sample (MS4), the 133with angular sizes <35" have been imaged at 5 GHz at 2"-4" resolutionwith the Australia Telescope Compact Array. More than 90% of the samplehas been reliably optically identified, either on the plates of the UKSchmidt Southern Sky Survey or on R-band CCD images made with theAnglo-Australian Telescope. A subsample of 137 sources, the SMS4,defined to be a close southern equivalent of the northern 3CRR sample,was found to have global properties mostly consistent with the northernsample. Linear sizes of MS4 galaxies and quasars were found to beconsistent with galaxy-quasar unification models of orientation andevolution.
| High-frequency radio observations of the Kühr sample and the epoch-dependent luminosity function of flat-spectrum quasars
We discuss our ATCA 18.5 and 22 GHz flux density measurements ofSouthern extragalactic sources in the complete 5 GHz sample of Kühret al. (1981, A&AS, 45, 367). The high frequency (5-18.5 GHz)spectral indices of steep-spectrum sources for which we have 18.5 GHzdata (66% of the complete sample) are systematically steeper than thelow frequency (2.7-5 GHz) ones, with median α^52.7 =0.76, median α18.55 = 1.18(Sν∝ ν-α), and median steepeningΔα = 0.32, and there is evidence of an anti-correlation ofΔα18.55 with luminosity. Thecompleteness of 18.5 GHz data is much higher (89%) for flat-spectrumsources (mostly quasars), which also exhibit a spectral steepening:median α^52.7=-0.14, medianα18.55=0.16 (Sν∝ν-α), and median Δα = 0.19. Takingadvantage of the almost complete redshift information on flat-spectrumquasars, we have estimated their 5 GHz luminosity function in severalredshift bins. The results confirm that their radio luminosity densitypeaks at z_peak ≃ 2.5 but do not provide evidence for deviationsfrom pure luminosity evolution as hinted at by other data sets. Acomparison of our 22 GHz flux densities with WMAP K-band data forflat-spectrum sources suggests that WMAP flux densities may be low by amedian factor of ≃1.2. The extrapolations of 5 GHz counts andluminosity functions of flat-spectrum radio quasars using the observeddistribution of the 5-18.5 GHz spectral indices match those deriveddirectly from WMAP data, indicating that the high frequency WMAP surveydoes not detect any large population of FSRQs with anomalous spectra.
| Stellar populations in a complete sample of local radio galaxies
We investigate the nature of the continuum emission and stellarpopulations in the inner 1-3 kpc of a complete sample of 24 southernradio galaxies, and we compare the results with a control sample of 18non-active early-type galaxies. 12 of the radio galaxies are classifiedas Fanaroff-Riley type I (FR I), eight as FR II and four as intermediateor undefined type (FR x). Optical long-slit spectra are used to performspectral synthesis as a function of distance from the nucleus at anaverage sampling of 0.5-1.0 kpc and to quantify the relativecontributions of a blue featureless continuum and stellar populationcomponents of different ages. Our main finding is a systematicdifference between the stellar populations of the radio and controlsample galaxies: the former have a larger contribution from anintermediate-age (1 Gyr) component, suggesting a connection between thepresent radio activity and a starburst which occurred ~1 Gyr ago. Inaddition, we find a correlation between the contribution of the 1-Gyrcomponent and the radio power, suggesting that more massive starburstshave led to more powerful radio emission. A similar relation is foundbetween the radio power and the mean age of the stellar population, inthe sense that stronger nuclear activity is found in younger galaxies.We also find that the stellar populations of FR I galaxies are, onaverage, older and more homogeneous than those of FR IIs. Significantpopulation gradients were found in only four radio galaxies, which arealso those with more than 10 per cent of their total flux at 4020Åcontributed by age components younger than 100 Myr and/or afeatureless continuum (indistinguishable from a 3-Myr-old stellarpopulation).
| X-Ray Emission Properties of Large-Scale Jets, Hot Spots, and Lobes in Active Galactic Nuclei
We examine a systematic comparison of jet knots, hot spots, and radiolobes recently observed with Chandra and ASCA. This report discusses theorigin of their X-ray emissions and investigates the dynamics of thejets. The data were compiled at well-sampled radio (5 GHz) and X-ray (1keV) frequencies for more than 40 radio galaxies. We examine threemodels for the X-ray production: synchrotron (SYN), synchrotronself-Compton (SSC), and external Compton (EC) on cosmic microwavebackground (CMB) photons. For the SYN sources-mostly jet knots in nearbylow-luminosity radio galaxies-X-ray photons are produced byultrarelativistic electrons with energies 10-100 TeV that must beaccelerated in situ. For the other objects, conservatively classified asSSC or EC sources, a simple formulation of calculating the ``expected''X-ray fluxes under an equipartition hypothesis is presented. We confirmthat the observed X-ray fluxes are close to the expected ones fornonrelativistic emitting plasma velocities in the case of radio lobesand the majority of hot spots, whereas a considerable fraction of jetknots are too bright in X-rays to be explained in this way. We examinetwo possibilities to account for the discrepancy in a framework of theinverse Compton model: (1) the magnetic field is much smaller than theequipartition value, and (2) the jets are highly relativistic onkiloparsec and megaparsec scales. We conclude that if the inverseCompton model is the case, the X-ray-bright jet knots are most likelyfar from the minimum-power condition. We also briefly discuss the otherpossibility, namely, that the observed X-ray emission from all the jetknots is synchrotron in origin.
| Stacking Searches for Gamma-Ray Emission above 100 MeV from Radio and Seyfert Galaxies
The EGRET telescope on board Compton Gamma Ray Observatory detected morethan 60 sources of high-energy gamma radiation associated with activegalactic nuclei (AGNs). All but one of those belong to the blazarsubclass; the only exception is the nearby radio galaxy Centaurus A.Since there is no obvious reason other than proximity to expect Cen A tobe the only nonblazar AGN emitting in high-energy gamma rays, we haveutilized the ``stacking'' technique to search for emission above 100 MeVfrom two nonblazar AGN subclasses, radio galaxies and Seyfert galaxies.Maps of gamma-ray counts, exposure, and diffuse background have beencreated, then co-added in varying numbers based on sorts by redshift, 5GHz flux density, and optical brightness, and finally tested forgamma-ray emission. No detection significance greater than 2 σ hasbeen found for any subclass, sorting parameter, or number of objectsco-added. Monte Carlo simulations have also been performed to validatethe technique and estimate the significance of the results.
| The ISOPHOT 170 μm Serendipity Survey II. The catalog of optically identified galaxies%
The ISOPHOT Serendipity Sky Survey strip-scanning measurements covering≈15% of the far-infrared (FIR) sky at 170 μm were searched forcompact sources associated with optically identified galaxies. CompactSerendipity Survey sources with a high signal-to-noise ratio in at leasttwo ISOPHOT C200 detector pixels were selected that have a positionalassociation with a galaxy identification in the NED and/or Simbaddatabases and a galaxy counterpart visible on the Digitized Sky Surveyplates. A catalog with 170 μm fluxes for more than 1900 galaxies hasbeen established, 200 of which were measured several times. The faintest170 μm fluxes reach values just below 0.5 Jy, while the brightest,already somewhat extended galaxies have fluxes up to ≈600 Jy. For thevast majority of listed galaxies, the 170 μm fluxes were measured forthe first time. While most of the galaxies are spirals, about 70 of thesources are classified as ellipticals or lenticulars. This is the onlycurrently available large-scale galaxy catalog containing a sufficientnumber of sources with 170 μm fluxes to allow further statisticalstudies of various FIR properties.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) areMPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena,Imperial College London.Full Table 4 and Table 6 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/39
| Inverse Compton X-rays from the radio galaxy 3C 219
We report the results from a Chandra observation of the powerful nearby(z= 0.1744) radio galaxy 3C 219. We find evidence for non-thermal X-rayemission from the radio lobes which fits fairly well with a combinationof inverse Compton scattering of Cosmic Microwave Background radiationand of nuclear photons with the relativistic electrons in the lobes. Thecomparison between radio synchrotron and IC emission yields a magneticfield strength significantly lower (~3) than that calculated underminimum energy conditions; the source energetics is then dominated bythe relativistic particles.
| Emission-Line Diagnostics of the Central Engines of Weak-Line Radio Galaxies
A handful of well-studied weak-line radio galaxies (WLRGs) have beentraditionally classified as low-ionization nuclear emission-line regions(LINERs), suggesting that these two groups of active galactic nuclei(AGNs) might be related. In this paper, we present new opticalemission-line measurements for 20 WLRGs, which we supplement withmeasurements for an additional four from the literature. Classifyingthese objects by their emission-line ratios, we find that 50% of theobjects are robustly classified as LINERs, while an additional 25% arelikely to be LINERs. Photoionization calculations show that the spectralenergy distribution of the well-studied WLRG 3C 270 (NGC 4261) is ableto produce the observed emission-line ratios, but only if the UVemission seen by the narrow emission line gas is significantly higherthan that observed, implying AV=2.5-4.2 mag along our line ofsight to the nucleus. From the photoionization calculations, we findthat the emission-line gas must have an ionization parameter between10-3.5 and 10-4.0 and a wide range in hydrogendensity (102-106 cm-3) to reproduce themeasured emission-line ratios, similar to the properties inferred forthe emission-line gas in LINERs. Thus, we find that properties of theemission-line gas as well as the underlying excitation mechanism areindeed similar in LINERs and WLRGs. By extension, the central engines ofaccretion-powered LINERs and WLRGs, which do host an accreting blackhole, may be qualitatively similar.
| 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
| The black hole mass of low redshift radiogalaxies
We make use of two empirical relations between the black hole mass andthe global properties (bulge luminosity and stellar velocity dispersion)of nearby elliptical galaxies, to infer the mass of the central blackhole (CM MBH) in low redshift radiogalaxies. Using the mostrecent determinations of black hole masses for inactive early typegalaxies we show that the bulge luminosity and the central velocitydispersion are almost equally correlated (similar scatter) with thecentral black-hole mass. Applying these relations to two large andhomogeneous datasets of radiogalaxies we find that they host black-holeswhose mass ranges from ~ 5*E7 to ~ 6*E9CMMsun (average ~ 8.9). CMMBH is found to be proportional to the mass of the bulge (CMMbulge). The distribution of the ratio CM MBH/CMMbulge has a mean value of 8*E-4 and shows ascatter that is consistent with that expected from the associatederrors. At variance with previous claims no significant correlation isinstead found between CM MBH (or CM Mbulge) andthe radio power at 5 GHz.
| Study of the X-Ray Background Spectrum and Its Large-Scale Fluctuation with ASCA
We studied the energy spectrum and the large-scale fluctuation of theX-ray background with the ASCA GIS instrument based on the ASCA MediumSensitivity Survey and Large Sky Survey observations. A total of 91fields with Galactic latitude |b| > 10° were selected with a skycoverage of 50 deg2 and 4.2 Ms of exposure. For each field,non-X-ray events were carefully subtracted and sources brighter than ~ 2× 1013 erg cm-2 s-1 (2-10keV)were eliminated. Spectral fits with a single power-law model for theindividual 0.7-10 keV spectra showed a significant excess below ~ 2keV,which could be expressed by an additional thermal model with kT ~= 0.4keV or a steep power-law model with a photon index ofΓsoft ~= 6. The 0.5-2keV intensities of the softthermal component varied significantly from field to field by 1 σ= 52 +4-5%, and showed a maximum toward theGalactic Center. This component is considered to be entirely Galactic.As for the hard power-law component, an average photon index of 91fields was obtained to be Γhard = 1.412 +/- 0.007 +/-0.025 and the average 2-10keV intensity was calculated asFhardX = (6.38 +/- 0.04 +/- 0.64) ×10-8erg cm-2 s-1 sr-1 (1σ statistical and systematic errors). The Galactic component ismarginally detected in the hard band. The 2-10keV intensities show a 1σ deviation of 6.49+0.56-0.61%, whiledeviation due to the reproducibility of the particle background is 3.2%.The observed deviation can be explained by the Poisson noise of thesource count in the f.o.v. (~ 0.5 deg2), even assuming asingle N-logS relation on the whole s ky. Based on the observedfluctuation and the absolute intensity, an acceptable region of theN-logS relation was derived, showing a consistent feature with therecent Chandra and XMM-Newton results. The fluctuation of the spectralindex was also examined; it implied a large amount of hard sources and asubstantial variation in the intrinsic source spectra(Γs ~= 1.1 +/- 1.0).
| Hybrid morphology radio sources and the Fanaroff-Riley dichotomy
We highlight a group of peculiar double radio sources we christenHYMORS: HYbrid MOrphology Radio Sources. These HYMORS appear to have anFR I type radio lobe on one side of the active nucleus but an FR II typelobe on the opposite side. Such objects range in size from /~0.01 Mpc to/~1 Mpc. The mere existence of these hybrid sources causes severedifficulties for models which attribute the differences between FR I andFR II radio sources to some intrinsic property of the compact centralengine, or the composition of the jet plasma. HYMORS support models forthe FR dichotomy based upon the interaction of the jet plasma with theambient medium, in that asymmetries in the external environment couldmore naturally produce the observed hybrid morphologies.
| Active Galactic Nucleus Black Hole Masses and Bolometric Luminosities
Black hole mass, along with mass accretion rate, is a fundamentalproperty of active galactic nuclei (AGNs). Black hole mass sets anapproximate upper limit to AGN energetics via the Eddington limit. Wecollect and compare all AGN black hole mass estimates from theliterature; these 177 masses are mostly based on the virial assumptionfor the broad emission lines, with the broad-line region size determinedfrom either reverberation mapping or optical luminosity. We introduce200 additional black hole mass estimates based on properties of the hostgalaxy bulges, using either the observed stellar velocity dispersion orthe fundamental plane relation to infer σ these methods assumethat AGN hosts are normal galaxies. We compare 36 cases for which blackhole mass has been generated by different methods and find, forindividual objects, a scatter as high as a couple of orders ofmagnitude. The less direct the method, the larger the discrepancy withother estimates, probably due to the large scatter in the underlyingcorrelations assumed. Using published fluxes, we calculate bolometricluminosities for 234 AGNs and investigate the relation between blackhole mass and luminosity. In contrast to other studies, we find nosignificant correlation of black hole mass with luminosity, other thanthose induced by circular reasoning in the estimation of black holemass. The Eddington limit defines an approximate upper envelope to thedistribution of luminosities, but the lower envelope depends entirely onthe sample of AGNs included. For any given black hole mass, there is arange in Eddington ratio of up to 3 orders of magnitude.
| Redshifts for a Sample of Radio-selected Poor Clusters
Multifiber optical spectroscopy has been performed on galaxies in thevicinity of strong, nearby radio galaxies. These radio galaxies wereselected from the 3CR and B2 catalogs based on their exclusion from theAbell catalog, which is puzzling given the hypothesis that an externalmedium is required to confine the radio plasma of such galaxies.Velocities derived from the spectra were used to confirm the existenceof groups and poor clusters in the fields of most of the radio galaxies.We find that all radio galaxies with classical Fanaroff-Riley type Imorphologies prove to reside in clusters, whereas the other radiogalaxies often appear to be recent galaxy-galaxy mergers in regions oflow galaxy density. These findings confirm the earlier result that theexistence of extended X-ray emission combined with a statistical excessof neighboring galaxies can be used to identify poor clusters associatedwith radio galaxies.
| The ASCA Medium Sensitivity Survey (the GIS Catalog Project): Source Catalog
We present the first X-ray source catalog of the ASCA Medium SensitivitySurvey (AMSS, or the GIS catalog project), constructed from data atGalactic latitudes b>10deg observed between 1993 May and 1996December. The catalog utilizes 368 combined fields and contains 1343sources with the detection significance above 5 σ either in thesurvey bands of 0.7-7 keV, 2-10 keV, or 0.7-2 keV, including targetsources. For each source, the ASCA source name, position, a 90% errorradius, count rates in the three bands, detection significances, fluxes,and a hardness ratio are provided. With extensive simulations, wecarefully evaluate the data quality of the catalog. Results fromcross-correlation with other existing catalogs are briefly summarized.
| X-Ray Measurements of the Field and Particle Energy Distributions in the West Lobe of the Radio Galaxy NGC 1316 (Fornax A)
A follow-up X-ray study was made of the west lobe of the radio galaxyFornax A (NGC 1316) that was based on new ASCA observations made in 1997for 98 ks and that incorporated the previous observation in 1994 for 39ks. The 0.7-10 keV spectrum of the emission can be described by a powerlaw with an energy index of 0.74+/-0.10, which agrees with thesynchrotron radio index of 0.9+/-0.2. Therefore, the X-rays arereconfirmed to arise via the inverse Compton scattering of the cosmicmicrowave photons, as Kaneda et al. and Feigelson et al. concluded. Thesurface brightness of the inverse Compton X-rays exhibits a relativelyflat distribution over the west lobe, indicative of an approximatelyspherical emissivity distribution with a radius of ~11' (75 kpc). Incontrast, the 1.4 GHz radio image by Ekers et al. exhibits arim-brightened surface brightness, consistent with a shell-likeemissivity distribution whose inner and outer boundaries are 4' and 11',respectively. These morphological differences between radio and X-rayssuggest that the relativistic electrons are distributed homogeneouslyover the lobe volume, whereas the magnetic field is amplified toward thelobe rim region.
| The fundamental plane of radio galaxies
We collected photometrical and dynamical data for 73 low red-shift(z<0.2) Radio Galaxies (LzRG) in order to study their FundamentalPlane (FP). For 22 sources we also present new velocity dispersion datathat complement the photometric data given in our previous study of LzRG(Govoni et al. \cite{Govoni00}a). It is found that the FP of LzRG issimilar to the one defined by non-active elliptical galaxies, with LzRGrepresenting the brightest end of the population of early type galaxies.Since the FP mainly reflects the virial equilibrium condition, ourresult implies that the global properties of early-type galaxies(defining the FP) are not influenced by the presence of gas accretion inthe central black hole. This is fully in agreement with the recentresults in black hole demography, showing that virtually all luminousspheroidal galaxies host a massive black hole and therefore maypotentially become active. We confirm and extend to giant ellipticalsthe systematic increase of the mass-to-light ratio with galaxyluminosity. Based on observations collected at European SouthernObservatory, La Silla, Chile.
| A radio continuum survey of the southern sky at 1420 MHz. The atlas of contour maps
The results of an absolutely calibrated radio continuum survey of theSouth Celestial Hemisphere at a frequency of 1420 MHz are presented.Contour maps show the area 0h <= RA <= 24hfor the declination range -90degr to -10degr . Contour steps (50 mKTB 3 x rms noise) and angular resolution (HPBW 35\farcm 4) ofthe maps match the already existing Stockert northern sky survey at thesame frequency. We compare flux densities of compact and extendedsources with published data from the Parkes 64-m telescope and findexcellent agreement in general. The survey maps are sensitive enough toconstrain synchrotron and thermal emission components which mightinfluence studies of the cosmic microwave background. Figures 1 and 2are also available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/376/861
| Are all radio galaxies genuine ellipticals?
Classical double radio sources are believed to be powered by a strongrelativistic jet due to the presence of a rapidly spinning black hole inthe center of a giant E galaxy formed by the merging of two galaxies. Ifthis is true, no radio source should have been found in spiral or S0galaxies. A number of radio S0s have been reported, but most of them areprobably misclassified Es. However, our own observations confirm thatNGC 612 is an S0 although it is associated with the FR II radio sourcePKS 0131-36. We conclude that S0s can be classical radio sources, butthat such occurences are extremely rare. Partly based on observationsobtained with the ESO 3.6 m telescope, La Silla, Chile.
| A radio continuum survey of the southern sky at 1420 MHz. Observations and data reduction
We describe the equipment, observational method and reduction procedureof an absolutely calibrated radio continuum survey of the SouthCelestial Hemisphere at a frequency of 1420 MHz. These observationscover the area 0h <= RA <= 24h fordeclinations less than -10degr . The sensitivity is about 50 mK T_B(full beam brightness) and the angular resolution (HPBW) is 35farcm4 ,which matches the existing northern sky survey at the same frequency.
| Extragalactic radio sources with hybrid morphology: implications for the Fanaroff-Riley dichotomy
We provide observational and theoretical perspectives on the currentlymuch debated issue of the Fanaroff-Riley (FR) morphological dichotomy ofextragalactic radio sources. In this context we introduce a new, albeitrare, class of double radio sources in which the two lobes exhibitclearly different FR morphologies. It is argued that such `HYbridMOrphology Radio Sources', or HYMORS, could be used to effectivelyconstrain the theoretical mechanisms proposed for the FR dichotomy.Basically, the existence of HYMORS supports explanations for the FRdichotomy based upon jet interaction with the medium external to thecentral engine, and appears quite difficult to reconcile with the classof explanations that posit fundamental differences in the centralengine, such as black hole spin or jet composition, to be responsiblefor the two FR classes of double radio sources.
| The optical properties of low redshift radio galaxies
We present morphological and photometric properties of 79 low redshift(z<=0.12) radio galaxies extracted from two radio flux limitedsamples of radio sources. All objects are imaged in the R band and for asubsample we have also obtained B band images. The sample includessources of both FRI and FRII radio morphological type. Through thedecomposition of the luminosity profiles and the analysis of thestructural profiles (ellipticity, PA, c4) of the galaxies we are able tocharacterize in detail the optical properties of the radio galaxies. Itis found that most of host galaxies are luminous bulge dominated systemssimilar to normal giant ellipticals. Some cases of additional diskcomponents are found whose spheroid-to-disk luminosity ratio is similarto that found in S0 galaxies. The average absolute magnitude is =-24.0 with a clear trend for FRI sources tobe ~ 0.5 mag brighter than FRII galaxies. In about 40% of the objectsobserved we find an excess of light in the nucleus that is attributed tothe presence of a nuclear point source whose luminosity is on average ~1-2% of the total flux of the host galaxy. The luminosity of thesenuclear point sources appears correlated with the core radio power ofthe galaxies. Radio galaxies follow the same mu_e - R_e relationship asnormal elliptical galaxies. The distribution of ellipticity, the amountof twisting and shape of isophotes (boxy, disky) do not differsignificantly from other ellipticals. The evidence for recentinteractions is therefore rather modest. Finally on average radiogalaxies are bluer and have a color dispersion larger than normalelliptical galaxies, and the average color gradient in radio galaxiesappears slightly steeper than in normal ellipticals. These resultssupport a scenario where radio emission is weakly related with theoverall properties and/or the activity have negligible effects on theglobal characteristics of the host galaxy. Based on observationscollected at the European Southern Observatory, La Silla, Chile. Basedon observations collected at the Nordic Optical Telescope, La Palma.
| An X-Ray Spectral Survey of Radio-loud Active Galactic Nuclei with ASCA
We present a uniform and systematic analysis of the 0.6-10 keV X-rayspectra of radio-loud active galactic nuclei (AGNs) observed by ASCA.The sample, which is not statistically complete, includes 10 broad-lineradio galaxies (BLRGs), five radio-loud quasars (QSRs), nine narrow-lineradio galaxies (NLRGs), and 10 radio galaxies (RGs) of mixed FR I and FRII types. For several sources the ASCA data are presented here for thefirst time. The exposure times of the observations and the fluxes of theobjects vary over a wide range; as a result, so does the signal-to-noiseratio of the individual X-ray spectra. At soft X-rays, about 50% ofNLRGs and 100% of RGs exhibit thermal plasma emission components, withbimodal distributions of temperatures and luminosities. This indicatesthat the emission in such an object arises in hot gas either in asurrounding cluster or loose group or in a hot corona, consistent withprevious ROSAT and optical results. At energies above 2 keV, a hardpower-law component (photon index Γ~1.7-1.8) is detected in 90% ofcases. The power-law photon indices and luminosities in BLRGs, QSRs, andNLRGs are similar. This is consistent with simple orientation-basedunification schemes for lobe-dominated radio-loud sources in whichBLRGs, QSRs, and NLRGs harbor the same type of central engine. Moreover,excess cold absorption in the range 1021-1024cm-2 is detected in most (but not all) NLRGs, consistent withabsorption by obscuring tori, as postulated by unification scenarios.The ASCA data provide initial evidence that the immediate gaseousenvironment of the X-ray source of BLRGs may be different than inSeyfert 1 galaxies: absorption edges of ionized oxygen, common in thelatter, are detected in only one BLRG. Instead we detect large columnsof cold gas in a fraction (~44%-60%) of BLRGs and QSRs, comparable tothe columns detected in NLRGs, which is puzzling. This difference hintsat different physical and/or geometrical properties of the medium aroundthe X-ray source in radio-loud AGNs compared to their radio-quietcounterparts, properties that can be explored further with future X-rayobservations. For the full sample, the nuclear X-ray luminosity iscorrelated with the luminosity of the [O III] emission line, the FIRemission at 12 μm, and the lobe radio power at 5 GHz. The Fe Kαline is detected in 50% of BLRGs and in one QSR, with a large range ofintrinsic widths and equivalent widths. In the handful of NLRGs where itis detected, the line is generally unresolved. Comparing the averagepower-law photon indices of the various classes of radio-loud AGNs totheir radio-quiet counterparts from the literature, we find only a weakindication that the ASCA 2-10 keV spectra of BLRGs are flatter thanthose of Seyfert 1 galaxies of comparable X-ray luminosity. This resultis at odds with evidence from samples studied by other authorssuggesting that radio-loud AGNs have flatter spectra than radio-quietones. Rather, it supports the idea that a beamed synchrotronself-Compton component related to the radio source (jet) is responsiblefor the flatter slopes in those radio-loud AGNs. We argue that, becauseof the way those samples were constructed, beamed X-ray emission fromthe radio jets probably contributed to the observed X-ray spectra. Thesample studied here includes six weak-line radio galaxies (WLRGs),powerful radio galaxies characterized by [O III] 4569 and 5007 Åof unusually low luminosity and by unusually high [O II]/[O III] lineratios. The ASCA spectra of WLRGs can be generally decomposed into asoft thermal component with kT~1 keV, plus a hard component, describedeither by a flat (<Γ>=1.5) absorbed power law or by a veryhot (kT~100 keV) thermal bremsstrahlung model. Their intrinsicluminosities are in the rangeL2-10keV~1040-1042 ergs s-1,2 orders of magnitude lower than in other sources in our sample. If thehard X-ray emission is attributed to a low-luminosity AGN, aninteresting possibility is that WLRGs represent an extreme population ofradio galaxies in which the central black hole is accreting at a ratewell below the Eddington rate.
| ASCA measurements of non-thermal pressures in the radio lobes
A summary is presented of ASCA (Tanaka et al. 1994) results oninverse-Comptonized X-rays from lobes of radio galaxies, which areemitted when relativistic electrons constructing synchrotron radio lobesboost up the cosmic microwave background photons to the X-ray andgamma-ray energy. By comparing the two radiation fluxes, we derived theenergy distribution between magnetic fields and the relativisticelectrons, assuming the same relativistic electrons in the lobes producethe emissions. This method is essentially free from the energyequipartition assumption. A study on spatial distributions of the fieldand particle energy densities is also presented. Based on the resultspresented in this paper, we suggest particle domination in the lobes andat the formation of the lobe.
| An X-Ray and Optical Investigation of the Environments around Nearby Radio Galaxies
Investigations of the cluster environment of radio sources have notshown a correlation between radio power and degree of clustering.However, it has been demonstrated that extended X-ray luminosity andgalaxy clustering do exhibit a positive correlation. This studyinvestigates a complete sample of 25 nearby (z<=0.06) radio galaxiesthat are not cataloged members of Abell clusters. The environment ofthese radio galaxies is studied in both the X-ray and the optical bymeans of the ROSAT All-Sky Survey (RASS), ROSAT pointed observations,and the Palomar optical Digitized Sky Survey (DSS). X-ray luminositiesand extents are determined from the RASS, and the DSS is used toquantify the degree of clustering via the spatial two-point correlationcoefficient, Bgg. Of the 25 sources, 20 are >=3 σdetections in the X-ray and 11 possessed Bgg's significantlyin excess of that expected for an isolated galaxy. Adding the criterionthat the X-ray emission be resolved, 10 of the radio galaxies do appearto reside in poor clusters with extended X-ray emission suggestive ofthe presence of an intracluster medium. Eight of these galaxies alsopossess high spatial correlation coefficients. Taken together, thesedata suggest that the radio galaxies reside in a low-richness extensionof the Abell clusters. The unresolved X-ray emission from the othergalaxies is most likely associated with active galactic nucleusphenomena. Furthermore, although the sample size is small, it appearsthat the environments of FR I and FR II sources differ. FR I's tend tobe more frequently associated with extended X-ray emission (10 of 18),whereas FR II's are typically point sources or nondetections in theX-ray (none of the seven sources exhibit extended X-ray emission).
| Radio-loud and Radio-quiet Active Galactic Nuclei
We have generated a sample of 409 active galactic nuclei (AGNs) forwhich both the radio luminosity at 5 GHz and the line luminosity in [OIII] lambda5007 have been measured. The radio luminosity spans a rangeof 10 orders of magnitude, and the [O III] line luminosity spans a rangeof 8 orders of magnitude-both considerably larger than the ranges inprevious studies. We show that these two quantities are correlated in asimilar way for both radio-loud and radio-quiet AGNs. We demonstratethat the observed correlation can be explained in terms of a model inwhich jets are accelerated and collimated by a vertical magnetic field.
| The nature of the optical-radio correlations for powerful radio galaxies
The nature of the optical-radio correlations for powerful radio galaxiesis investigated using spectroscopic observations of a complete sample ofsouthern 2-Jy radio sources. In line with previous work, we find thatsignificant correlations exist between the luminosities of the[OIII]lambda5007, [OII]lambda3727 and Hβ emission lines and the radioluminosity. However, our observations are not easily reconciled with theidea that these correlations are caused by the increase in the power ofthe photoionizing quasar as the jet power increases, with average ISMproperties not changing appreciably with redshift or radio power: notonly do we find that the scatter in the L_[Oiii] versus L_radiocorrelation is significantly larger than in L_[Oii] versus L_radio andL_Hβ versus L_radio correlations, but the ionization state deducedfrom the emission lines does not increase with radio power as predictedby the simple, constant ISM, photoionization model. We conclude that (a)there exists a considerable range in the quasar ionizing luminosity at agiven redshift, and (b) the mean density of the emission-line clouds islarger in the high-redshift/high-power radio sources. The latter densityenhancement may be either a consequence of the increased importance ofjet-cloud interactions or, alternatively, the result of a higherpressure in the confining hot ISM, in the high-redshift objects. Apartfrom the general scatter in the correlations, we identify a distinctgroup of objects with [OIII]lambda5007 luminosities which are more thanan order of magnitude lower than in the general population radiogalaxies at similar redshift. These weak-line radio galaxies (WLRGs) arelikely to be sources in which the central ionizing quasars areparticularly feeble. Deep spectra show that many of the sources in oursample are broad-line radio galaxies (BLRGs). The fact that the BLRGsare observed out to the redshift limit of the survey, overlapping inredshift with the quasars, argues against the idea that BLRGs are simplythe low-radio-power counterparts of high-power, high-redshift quasars.Either there exists a considerable range in the intrinsic luminositiesof the broad-line AGN for a given redshift or radio power, or the BLRGsrepresent partially obscured quasars. The degree of scatter present inthe L_[Oiii] versus L_radio correlation supports the former possibility.
| 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.
| The Southern Sky Redshift Survey
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
| Properties of Very Luminous Galaxies
Recent analysis of the data from the Southern Sky Redshift Surveyextension (SSRS2) based on cell counts and the two-point correlationfunction has shown that very luminous galaxies are much more stronglyclustered than fainter galaxies. In fact, the amplitude of thecorrelation function of very luminous galaxies (L > L^*)asymptotically approaches that of R >= 0 clusters. In this paper weinvestigate the properties of the most luminous galaxies, with blueabsolute magnitudes M_B <= -21. We find that (1) the population mixis comparable to that in other ranges of absolute magnitude; (2) only asmall fraction are located in bona fide clusters; (3) the brightgalaxy-cluster cross-correlation function is significantly higher onlarge scales than that measured for fainter galaxies; (4) thecorrelation length of galaxies brighter than M_B ~ -20.0, expressed as afunction of the mean interparticle distance, appears to follow theuniversal dimensionless correlation function found for clusters andradio galaxies; (5) a large fraction of the bright galaxies are ininteracting pairs, while others show evidence for tidal distortions andsome appear to be surrounded by faint satellite galaxies. We concludethat very luminous optical galaxies differ from the normal population ofgalaxies in both clustering and other respects. We speculate that thispopulation is a highly biased tracer of mass, being associated with darkhalos with masses more comparable to clusters than to typical loosegroups.
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