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Jet speeds in wide-angle tailed radio galaxies
We present a sample of 30 wide-angle tailed radio galaxies (WATs) thatwe use to constrain the jet speeds in these sources. We measure thedistribution of the jet-sidedness ratios for the sample, and assumingthat the jets are beamed, the jet speeds in the range (0.3-0.7)c areobtained. Whilst the core prominence of the sample, which ought to be areliable indicator of beaming, shows little correlation with the jetsidedness, we argue that due to the peculiar nature of the WATs, coreprominence is unlikely to be a good indicator of beaming in thesesources. We further show that if the jets are fast and light, then thegalaxy speeds required to bend the jets into C-shapes such as those seenin 0647+693 are reasonable for a galaxy in a merging or recently mergedcluster.
| 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.
| Gamma-ray emissions of AGN and cosmological standard candles
In this work, we compile a sample which contains 71 GeV Gamma-ray-loudActive Galactic Nuclei (AGNs) (14 BL Lacs and 57 FSRQs), 53 FR I radiogalaxies and 63 FR II radio galaxies. We make a nonlinear least-squarefit to this sample, and find that the best fit value of the Hubbleconstant is H0=71.5±3.8 kms-1Mpc-1 with a reduced χ ~= 2.46 by assumingMv = -23.0 and accepting q0 = 1.0, and thecorresponding regression line has a correlation index R ~= 0.78. Thebest fit value of H0 = 71.5±3.8 kms-1Mpc-1 is in well agreement with H0 =72±8 km s-1 obtained by the Hubble Space TelescopeKey Project. Our results show that the GeV Gamma-ray emissions of AGNscan be used as cosmological standard candles indeed.
| The Epochs of Early-Type Galaxy Formation as a Function of Environment
The aim of this paper is to set constraints on the epochs of early-typegalaxy formation through the ``archaeology'' of the stellar populationsin local galaxies. Using our models of absorption-line indices thataccount for variable abundance ratios, we derive ages, totalmetallicities, and element ratios of 124 early-type galaxies in high-and low-density environments. The data are analyzed by comparison withmock galaxy samples created through Monte Carlo simulations taking thetypical average observational errors into account, in order to eliminateartifacts caused by correlated errors. We find that all threeparameters, age, metallicity, and α/Fe ratio, are correlated withvelocity dispersion. We show that these results are robust againstrecent revisions of the local abundance pattern at high metallicities.To recover the observed scatter we need to assume an intrinsic scatterof about 20% in age, 0.08 dex in [Z/H], and 0.05 dex in [α/Fe].All low-mass objects withM*<~1010Msolar (σ<~130kms-1) show evidence for the presence of intermediate-agestellar populations with low α/Fe ratios. About 20% of theintermediate-mass objects with1010<~M*/Msolar<~1011[110<~σ/(kms-1)<~230 both elliptical andlenticular galaxies] must have either a young subpopulation or a bluehorizontal branch. On the basis of the above relationships, valid forthe bulk of the sample, we show that the Mg-σ relation is mainlydriven by metallicity, with similar contributions from the α/Feratio (23%) and age (17%). We further find evidence for an influence ofthe environment on the stellar population properties. Massive early-typegalaxies in low-density environments seem on average ~2 Gyr younger andslightly (~0.05-0.1 dex) more metal-rich than their counterparts inhigh-density environments. No offsets in the α/Fe ratios areinstead detected. With the aid of a simple chemical evolution model, wetranslate the derived ages and α/Fe ratios into star formationhistories. We show that most star formation activity in early-typegalaxies is expected to have happened between redshifts ~3 and 5 inhigh-density environments and between redshifts 1 and 2 in low-densityenvironments. We conclude that at least 50% of the total stellar massdensity must have already formed at z~1, in good agreement withobservational estimates of the total stellar mass density as a functionof redshift. Our results suggest that significant mass growth in theearly-type galaxy population below z~1 must be restricted to lessmassive objects, and a significant increase of the stellar mass densitybetween redshifts 1 and 2 should be present, caused mainly by the fieldgalaxy population. The results of this paper further imply the presenceof vigorous star formation episodes in massive objects at z~2-5 andevolved elliptical galaxies around z~1, both observationally identifiedas SCUBA galaxies and extremely red objects, respectively.
| An X-Ray View of Weak-Line Radio Galaxies/LINERs
We present X-ray observations of nine weak-line radio galaxies (WLRGs),optically classified as confirmed or possible LINERs. The data weretaken from the Chandra, XMM-Newton, and BeppoSAX archives. The Chandraimages typically show complex X-ray morphologies, with hard (2-10 keV)point sources embedded in diffuse soft (0.3-2.0 keV) emission in allcases except those of 1246-41 (NGC 4696), in which only diffuse emissionis detected on the scale of the cluster, and 0334-01 (3C 15), in whichonly a point source is detected. The nuclear X-ray spectra are wellfitted at hard energies by an absorbed power law, with a wide range ofphoton indices, Γ=1.5-2.7. Excess absorption over the Galacticvalue is detected in six of the nine sources, with column densitiesNH~1021-1022 cm-2. A thermalcomponent is required at softer energies, in agreement with the resultsof the spatial analysis. We find that there is no correlation betweenthe core X-ray luminosity and the radio core dominance parameter,suggesting that the bulk of the core X-ray emission is not beamed butrather is isotropic and thus likely related to the accretion flow. In anattempt to constrain the nature of the accretion flow, we calculate theratios of bolometric to Eddington luminosities,Lbol/LEdd, and the radiative efficiency ηbased on the Bondi accretion rates. We find thatLbol/LEdd~10-4-10-6 andη~10-2-10-6 for all the objects in our sample,suggesting radiatively inefficient accretion flows.
| A sample of X-ray emitting normal galaxies from the BMW-HRI Catalogue
We obtained a sample of 143 normal galaxies with X-ray luminosity in therange 1038{-}1043 erg s-1 from thecross-correlation of the ROSAT HRI Brera Multi-scale Wavelet (BMW-HRI)Catalogue with the Lyon-Meudon Extragalactic Database (LEDA). We findthat the average X-ray properties of this sample are in good agreementwith those of other samples of galaxies in the literature. We selected acomplete flux limited serendipitous sample of 32 galaxies from which wederived the log N-log S distribution of normal galaxies in the fluxrange 1.1{-} 110 × 10-14 erg cm-2s-1. The resulting distribution is consistent with theEuclidean -1.5 slope. Comparisons with other samples, such as theExtended Medium Sensitivity Survey, the ROSAT All Sky Survey, theXMM-Newton/2dF survey, and the Chandra Deep Field Survey indicate thatthe log N -log S distribution of normal galaxies is consistent with aEuclidean slope over a flux range of about 6 decades.
| A dichotomy in the orientation of dust and radio jets in nearby low-power radio galaxies
We examine the properties of central dust in nearby quiescent and activeearly-type galaxies. The active galaxies are low-power radio galaxieswith Fanaroff & Riley type I or I/II radio jets. We focus on (a) thecomparison of the dust distributions in the active and quiescent galaxysamples; and (b) the relation between the radio jet and dustorientations. Our main observational conclusions are: (i) in line withprevious studies, the dust detection rate is higher in radio-jetgalaxies than in non radio-jet galaxies; (ii) radio galaxies contain ahigher fraction of regular dust “ellipses” compared toquiescent galaxies which contain more often irregular dustdistributions; (iii) the morphology, size and orientation of dustellipses and lanes in quiescent early-types and active early-types withkpc-scale radio jets is very similar; (iv) dust ellipses are alignedwith the major axis of the galaxy, dust lanes do not show a preferredalignment except for large (>kpc) dust lanes which are aligned withthe minor axis of the galaxy; and (v) as projected on the sky, jets donot show a preferred orientation relative to the galaxy major axis (andhence dust ellipses), but jets are preferentially perpendicular to dustlanes. We show that the dust ellipses are consistent with being nearlycircular thin disks viewed at random viewing angles. The lanes arelikely warped dust structures, which may be in the process of settlingdown to become regular disks or are being perturbed by anon-gravitational force. We use the observed dust-jet orientations toconstrain the three-dimensional angle θDJ between jetand dust. For dust-lane galaxies, the jet is approximately perpendicularto the dust structure, while for dust-ellipse galaxies there is a muchwider distribution of θDJ. We discuss two scenariosthat could explain the dust/jet/galaxy orientation dichotomy. If lanesare indeed settling, then the jet orientation apparently is roughlyaligned with the angular momentum of the dust before it settles. Iflanes are perturbed by a jet-related force, it appears that it causesthe dust to move out of its equilibrium plane in the galaxy into a planewhich is perpendicular to the jet.
| Jet termination in wide-angle tail radio sources
Wide-angle tail radio galaxies (WATs) are an uncommon class of radiosources with luminosities near the FR I/FR II break, and are usuallyassociated with central cluster galaxies. Their defining characteristicwhen imaged sensitively at high resolution is their twin,well-collimated jets, which can persist with low opening angle for tensof kiloparsecs before flaring into long, often bent, plumes. Althoughseveral models for the jet termination have been proposed, the majorityof them are unsatisfactory when confronted with observations. Here wepresent the results of a programme of radio observations made with theaims of showing that objects classified as WATs do all havewell-collimated jets and of seeing in detail how the jets disrupt asthey enter the plumes. We show that compact, `hotspot-like' features atthe ends of the jets are common but by no means universal, and discussthe constraints that this places on models of the jet-plume transition.We discuss the properties of the observed well-collimated jets, and,using relativistic beaming models, estimate their speed to be ~0.3c.Finally, we show that the distance from the galactic centre at which thebase of the plume is found is related to the temperature of the hostcluster.
| K-band Properties of Galaxy Clusters and Groups: Brightest Cluster Galaxies and Intracluster Light
We investigate the near-infrared K-band properties of the brightestcluster galaxies (BCGs) in a sample of 93 X-ray galaxy clusters andgroups, using data from the Two Micron All Sky Survey. Our clustersample spans a factor of 70 in mass, making it sensitive to any clustermass-related trends. We derive the cumulative radial distribution forthe BCGs in the ensemble and find that 70% of the BCGs are centered inthe cluster to within 5% of the virial radius r200; thisquantifies earlier findings that BCG position coincides with the clustercenter as defined by the X-ray emission peak. We study the correlationsbetween the luminosity of the BCGs (Lb) and the mass and theluminosity of the host clusters, finding that BCGs in more massiveclusters are more luminous than their counterparts in less massivesystems and that the BCGs become less important in the overall clusterlight (L200) as cluster mass increases. By examining a largesample of optically selected groups, we find that these correlationshold for galactic systems less massive than our clusters(<3×1013 Msolar). From the differencesbetween luminosity functions in high- and low-mass clusters, we arguethat BCGs grow in luminosity mainly by merging with other luminousgalaxies as the host clusters grow hierarchically; the decreasing BCGluminosity fraction (Lb/L200) with cluster massindicates that the rate of luminosity growth in BCGs is slow compared tothe rate at which clusters acquire galaxy light from the field or othermerging clusters. Utilizing the observed correlation between the clusterluminosity and mass and a merger tree model for cluster formation, weestimate that the amount of intracluster light (ICL) increases withcluster mass; our calculations suggest that in 1015Msolar clusters more than 50% of total stellar mass is inICL, making the role of ICL very important in the evolution andthermodynamic history of clusters. The cluster baryon fractionaccounting for the ICL is in good agreement with the value derived fromcosmic microwave background observations. The inclusion of ICL reducesthe discrepancy between the observed cluster cold baryon fraction andthat found in hydrodynamical simulations. Based on the observed ironabundance in the intracluster medium, we find that the ICL predicted byour model, together with the observed galaxy light, match the ironmass-to-light ratio expected from simple stellar population models,provided that the Salpeter initial mass function is adopted. The ICLalso makes it easier to produce the ``iron excess'' found in the centralregions of cool-core clusters.
| 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.
| Optical nuclei of radio-loud AGN and the Fanaroff-Riley divide
We investigate the nature of the point-like optical nuclei that havebeen found in the centres of the host galaxies of a majority of radiogalaxies by the Hubble Space Telescope. We examine the evidence thatthese optical nuclei are relativistically beamed, and look fordifferences in the behaviour of the nuclei found in radio galaxies ofthe two Fanaroff-Riley types. We also attempt to relate this behaviourto the properties of the optical nuclei in their highly beamedcounterparts (the BL Lac objects and radio-loud quasars) as hypothesizedby the simple Unified Scheme. Simple model-fitting of the data suggeststhat the emission may be coming from a non-thermal relativistic jet. Itis also suggestive that the contribution from an accretion disk is notsignificant for the FRI objects and for the narrow-line radio galaxiesof FRII type, while it may be significant for the Broad-line objects,and consistent with the idea that the FRII optical nuclei seem to sufferfrom extinction due to an obscuring torus while the FRI optical nucleido not. These results are broadly in agreement with the Unified Schemefor radio-loud AGNs.Appendix C is only available in electronic form athttp://www.edpsciences.org
| 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.
| Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| The Ultraviolet Continuum Emission of FR I and FR II Radio Galaxies and a Proposal for a Unified AGN Model for FR I sources
This paper is the second in a series of two on the UV continuum emission(in the range from 1400 to 3700 Å) of radio galaxies that wereextracted from the Hubble Space Telescope (HST) Archives. The sampleconsists of 31 3C and Parkes radio galaxies that have redshifts below0.2 (the majority have redshifts of ~0.03) and radio powers of~1025-1027 W Hz-1 (usingH0=50 km-1 s-1 Mpc andq0=0.0). Paper I describes the sample selection and theproperties of individual sources; this paper deals with the analysis. Wefind that only about half the radio galaxies display any UV flux atwavelengths shorter than 2300 Å. More specifically, those galaxiesthat are dominated by a nuclear UV component are either BL Lac objectsor radio galaxies with broad emission lines. We detect a nuclear and anextended UV component only among half the radio galaxies with narrowemission lines. Although we do not find a correlation of the UVluminosity with emission-line luminosity or radio power, there doesappear to be a dependence on radio morphology. While (narrow line) FR IIsources do not show a nuclear UV component, FR I's do, however, only ifthey also have an optical jet (this is the case for seven of 21 FR I's).These results are broadly consistent with orientation-dependentunification models. In radio galaxies in which the torus does notobscure our view of the engine, the observed UV radiation appears to bepoint source-like. This is the case for broad-line radio galaxies and BLLac objects. In other radio galaxies that are oriented at an angle tous, the torus presumably blocks the nuclear UV component. Thenarrow-line FR I galaxies with optical jets can then be interpreted asobjects at a critical angle at which some, but not all, nuclear UVemission is blocked. The UVλ luminosities (withλ ranging from 1400 to 3700 Å) and theUVλ-V colors of radio galaxies show a larger scatterthan those of radio-quiet elliptical galaxies. At wavelengths shorterthan 2300 Å, some radio galaxies have on average bluer colors, butbeyond 3000 Å, their colors are on average slightly redder. Thispicture is also consistent with unification models-the galaxies withbluer colors are either BL Lac objects or broad-line radio galaxies. Allother radio galaxies (including the jetted FR I's) have somewhat reddercolors than radio-quiet elliptical galaxies. We suspect that this isprimarily due to reddening by dust, which we know is present in some ofthe radio galaxies in the sample. At longer wavelengths (>3000 Å),all radio galaxies (14 of 14) show an extended component. The morphologyof the extended emission is in most, but not all, cases comparable tothe morphology at optical wavelengths, implying that this is likely tobe starlight. However, the polarization images of two of seven radiogalaxies indicate that scattered light from the active galactic nucleusmay also contribute toward the UV luminosity.
| 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.
| The nuclear dust disks of five nearby 3CR elliptical galaxies
We present broad- and narrow-band WFPC2 images of the nuclear dust disksand rings of five low-/z elliptical galaxies hosting 3C radio sources:NGC 383 (3C 31)/NGC 382, NGC 3862 (3C 264), NGC 4261 (3C 270), UGC 12064(3C 449), and NGC 7720 (3C 465)/NGC 7720A. We detect resolved lineemission in all the disks. In NGC 383, the line emission consists of a``bar'' and spectacular filamentary arms to the north and south while inNGC 7720 and UGC 12064, it is extended along the major axis of thedisks, suggesting a true physical association between the ionizedmaterial and the dust. The color maps clearly reveal that the disks ofNGC 383, NGC 4261, NGC 7720, and possibly NGC 3862 are inclined. Thedisk of NGC 383 is the most disturbed and filamentary and appears toconsist of an ``inner'' (/~0.5 kpc) and ``outer'' (/~2.5 kpc) disk. Wesuggest that the colors of the unresolved nuclei of NGC 383 and NGC 3862may be partially accounted for by optical synchrotron emission (and mayin fact dominate in NGC 3862) while in NGC 4261, the nuclear emission iscompletely dominated by line emission. The disk colors are generallyredder than predicted by a simple ``sandwich'' model, suggesting thatthe disks cannot be simply treated as thin uniform sheets of dust. Wehave begun exploring radiative transfer models with varying dustcomposition, temperature, and distribution and preliminary results arevery promising.
| A catalogue and analysis of local galaxy ages and metallicities
We have assembled a catalogue of relative ages, metallicities andabundance ratios for about 150 local galaxies in field, group andcluster environments. The galaxies span morphological types from cD andellipticals, to late-type spirals. Ages and metallicities were estimatedfrom high-quality published spectral line indices using Worthey &Ottaviani (1997) single stellar population evolutionary models. Theidentification of galaxy age as a fourth parameter in the fundamentalplane (Forbes, Ponman & Brown 1998) is confirmed by our largersample of ages. We investigate trends between age and metallicity, andwith other physical parameters of the galaxies, such as ellipticity,luminosity and kinematic anisotropy. We demonstrate the existence of agalaxy age-metallicity relation similar to that seen for local galacticdisc stars, whereby young galaxies have high metallicity, while oldgalaxies span a large range in metallicities. We also investigate theinfluence of environment and morphology on the galaxy age andmetallicity, especially the predictions made by semi-analytichierarchical clustering models (HCM). We confirm that non-clusterellipticals are indeed younger on average than cluster ellipticals aspredicted by the HCM models. However we also find a trend for the moreluminous galaxies to have a higher [Mg/Fe] ratio than the lowerluminosity galaxies, which is opposite to the expectation from HCMmodels.
| Ultraviolet Hubble Space Telescope Snapshot Survey of 3CR Radio Source Counterparts at Low Redshift
We present UV images of 27 3CR radio galaxies with redshifts z<0.1that have been imaged with the Space Telescope Imaging Spectrograph(STIS) on board the Hubble Space Telescope (HST). The observationsemployed the NUV MAMA and broadband filters with peak sensitivity at2200 Å. We find that the UV luminosities show approximately afactor of 10-100 higher dispersion than the optical. We compare the UVmorphologies with optical V- and R-band WFPC2 snapshot survey images. Wehave found dramatic, complex, and extended UV emission from radiogalaxies even at zero redshift. We find a diverse range of UVmorphologies, some completely divergent from their visual morphology,which are reminiscent of the chaotic high-z radio galaxy structures seenin rest-frame UV. The UV morphologies show regions of star formation,jets, and possible scattered active galactic nucleus continuum. The UVemission is generally not aligned with the radio structure. We alsodetect the diffuse UV emission of the host galaxy. We propose that theseare the same physical phenomena as observed at high redshift, but on asmaller spatial scale.
| 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.
| The Orientation of Jets Relative to Dust Disks in Radio Galaxies
We use Hubble Space Telescope broadband images and VLA and VLBIcontinuum data to study the three-dimensional orientation of jetsrelative to nuclear dust disks in 20 radio galaxies. The comparisonbetween the position angles of the jets and those of the dust disk majoraxes shows a wide distribution, suggesting that they are not alignedpreferentially perpendicular to each other. We use a statisticaltechnique to determine the three-dimensional distribution of anglesbetween jets and dust disk rotation axes. This analysis shows that theobservations are consistent with jets homogeneously distributed over alarge region, extending over polar caps of 55°-77° but seemingto avoid lying close to the plane of the dust disks. We argue that thelack of close alignment between jets and dust disks axes is not likelyto be caused by feeding the nucleus with gas from mergers originatedfrom random directions. We suggest that the misalignment can be due to awarping mechanism in the accretion disk, such as self-irradiationinstability or the Bardeen-Petterson effect, or that the gravitationalpotential in the inner regions of the galaxy is misaligned with respectto that of the dust disk. Based partly on observations made with theNASA/ESA Hubble Space Telescope, which is operated by the Association ofUniversities for Research in Astronomy, Inc., under NASA contractNAS5-26555.
| The Nuclei of Radio Galaxies in the Ultraviolet: The Signature of Different Emission Processes
We have studied the nuclei of 28 radio galaxies from the 3CR sample inthe UV band. Unresolved nuclei (central compact cores: CCCs) areobserved in 10 of the 13 FR I galaxies, and in five of the 15 FR IIgalaxies. All sources that do not have a CCC in the optical do not havea CCC in the UV. Two FR I galaxies (3C 270 and 3C 296) have a CCC in theoptical but do not show the UV counterpart. Both of them show largedusty disks observed almost edge-on, possibly implying that they play arole in obscuring the nuclear emission. We have measured optical-UVspectral indices αo,UV between ~0.6 and ~7.0(Fν~ν-α). Broad-line radio galaxieshave the flattest spectra, and their values of αo,UVare also confined to a very narrow range. This is consistent withradiation produced in a geometrically thin, optically thick accretiondisk. On the other hand, FR I nuclei, which are most plausiblyoriginated by synchrotron emission from the inner relativistic jet, showa wide range of αo,UV. There is a clear trend withorientation in that sources observed almost edge-on or with clear signsof dust absorption have the steepest spectra. These observations implythat in FR I galaxies, obscuration can be present, but the obscuringmaterial is not in a ``standard'' geometrically thick torus. The moststriking difference between these absorbing structures and the classicactive galactic nucleus ``tori'' resides in the lower optical depth ofthe FR I galaxy obscuring material. Based on observations obtained atthe Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| Redshift-Distance Survey of Early-Type Galaxies. I. The ENEARc Cluster Sample
This paper presents data on the ENEARc subsample of the larger ENEARsurvey of nearby early-type galaxies. The ENEARc galaxies belong toclusters and were specifically chosen to be used for the construction ofa Dn-σ template. The ENEARc sample includes newmeasurements of spectroscopic and photometric parameters (redshift,velocity dispersion, line index Mg2, and the angular diameterdn), as well as data from the literature. New spectroscopicdata are given for 229 cluster early-type galaxies, and new photometryis presented for 348 objects. Repeat and overlap observations withexternal data sets are used to construct a final merged catalogconsisting of 640 early-type galaxies in 28 clusters. Objectivecriteria, based on catalogs of groups of galaxies derived from completeredshift surveys of the nearby universe, are used to assign galaxies toclusters. In a companion paper, these data are used to construct thetemplate Dn-σ distance relation for early-typegalaxies, which has been used to estimate galaxy distances and derivepeculiar velocities for the ENEAR all-sky sample. Based on observationsat Complejo Astronomico El Leoncito, operated under agreement betweenthe Consejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; Cerro Tololo Inter-American Observatory,National Optical Astronomical Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation; the EuropeanSouthern Observatory (ESO), partially under the ESO-ON agreement; theFred Lawrence Whipple Observatory; the Observatório do Pico dosDias, operated by the Laboratório Nacional de Astrofísicaand the MDM Observatory at Kitt Peak.
| Understanding the nature of FR II optical nuclei: A new diagnostic plane for radio galaxies
We extend our study of the nuclei of 3CR FR II radio galaxies throughHST optical images up to z = 0.3. In the majority of them an unresolvednucleus (central compact core, CCC) is found. We analyze their positionin the plane formed by the radio and optical nuclear luminosities inrelation to their optical spectral properties. The broad-lined objects(BLO) have the brightest nuclei: they are present only at opticalluminosities nu Lnu >~ 4x 1042 ergs-1 which we suggest might represent a threshold in theradiative efficiency combined with a small range of black hole masses.About 40% of the high and low excitation galaxies (HEG and LEG) show CCCwhich resemble those previously detected in FR I galaxies, in apparentcontrast to the unification model. The equivalent width of the [OIII]emission line (with respect to the nuclear luminosity) reveals thenature of these nuclei, indicating that the nuclei of HEG are obscuredto our line of sight and only scattered radiation is observed. Thisimplies that the population of FR II is composed of objects withdifferent nuclear properties, and only a fraction of them can be unifiedwith quasars. Based on observations obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Incorporated, under NASA contract NAS5-26555.
| The Parkes quarter-Jansky flat-spectrum sample. I. Sample selection and source identifications
We present a new sample of quarter-Jansky flat-spectrum radio sourcesselected to search for high-redshift quasars and to study the evolutionof the flat-spectrum quasar population. The sample comprises 878 radiosources selected from the Parkes catalogues with spectral indices alpha5 GHz_2.7 GHz >=-0.4 where Snu ~ nu alpha. The sample covers all right ascensions and the declination rangefrom -80fdg0 to +2fdg5 , excluding low galactic latitudes (mid b mid< 10deg) and the Magellanic Cloud regions. We haveobtained improved radio source positions, firstly to reconfirm themajority of the existing identifications, and secondly, using digitizedsky-survey data and deep B, Gunn-i and Gunn-z CCD-imaging, to findoptical identifications for 223 previously-unidentified sources. Wepresent the final catalogue of 878 flat-spectrum sources: 827 arecompact radio sources identified with galaxies, quasars and BL Lacobjects, 38 have either extended radio structure or are identified withGalactic objects (PN, HII or non-compact radio source), 4 are obscuredby Galactic stars, and 9 (1 per cent of the total sample) remainunidentified. Full Appendices A-D are only available in electronic format http://www.edpsciences.org
| A new list of extra-galactic radio jets
A catalogue of extra-galactic jets is very useful both in observationaland theoretical studies of active galaxies. With the use of new powerfulradio instruments, the detailed structures of very compact or weak radiosources are investigated observationally and many new radio jets aredetected. In this paper, we give a list of 661 radio sources withdetected radio jets known to us prior to the end of December 2000. Allreferences are collected for the observations of jets in radio, IR,optical, UV and X-ray wave-bands. Table 1 and references to Table 1 areonly 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/381/757
| A catalogue and analysis of X-ray luminosities of early-type galaxies
We present a catalogue of X-ray luminosities for 401 early-typegalaxies, of which 136 are based on newly analysed ROSAT PSPC pointedobservations. The remaining luminosities are taken from the literatureand converted to a common energy band, spectral model and distancescale. Using this sample we fit the LX:LB relationfor early-type galaxies and find a best-fit slope for the catalogue of~2.2. We demonstrate the influence of group-dominant galaxies on the fitand present evidence that the relation is not well modelled by a singlepower-law fit. We also derive estimates of the contribution to galaxyX-ray luminosities from discrete-sources and conclude that they provideLdscr/LB~=29.5ergs-1LBsolar-1. Wecompare this result with luminosities from our catalogue. Lastly, weexamine the influence of environment on galaxy X-ray luminosity and onthe form of the LX:LB relation. We conclude thatalthough environment undoubtedly affects the X-ray properties ofindividual galaxies, particularly those in the centres of groups andclusters, it does not change the nature of whole populations.
| Cold gas in elliptical galaxies
We explore the evolution of the cold gas (molecular and neutralhydrogen) of elliptical galaxies and merger remnants ordered into a timesequence on the basis of spectroscopic age estimates. We find that thefraction of cold gas in early merger remnants decreases significantlyfor ~1-2Gyr, but subsequent evolution toward evolved elliptical systemssees very little change. This trend can be attributed to an initial gasdepletion by strong star formation, which subsequently declines toquiescent rates. This explanation is consistent with the merger picturefor the formation of elliptical galaxies. We also explore the relationbetween the HI-to-H2 mass ratio and spectroscopic galaxy age,but find no evidence for a statistically significant trend. Thissuggests little net HI-to-H2 conversion for the systems inthe present sample.
| Structural evolution in elliptical galaxies: the age-shape relation
We test the hypothesis that the apparent axial ratio of an ellipticalgalaxy is correlated with the age of its stellar population. We findthat old ellipticals (with estimated ages t>7.5Gyr) are rounder onaverage than younger ellipticals. The statistical significance of thisshape difference is greatest at small radii; a Kolmogorov-Smirnov testcomparing the axial ratios of the two populations at R=Re/16yields a statistical significance greater than 99.96 per cent. Therelation between age and apparent shape is linked to the core/power-lawsurface brightness profile dichotomy. Core ellipticals have olderstellar populations, on average, than power-law ellipticals and arerounder in their inner regions. Our findings are consistent with ascenario in which power-law ellipticals are formed in gas-rich mergers,while core ellipticals form in dissipationless mergers, with coresformed and maintained by the influence of a binary black hole.
| Hi absorption in radio galaxies: effect of orientation or interstellar medium?
A search for Hi absorption has been made in 23 radio galaxies selectedfrom a complete sample. The observations were made with the AustraliaTelescope Compact Array (ATCA), with the Very Large Array (VLA) and forone galaxy with the Westerbork Synthesis Radio Telescope (WSRT). In fivegalaxies Hi absorption was detected. We investigate how the detectionrate is distributed among galaxies with different radio and opticalproperties. Among the Fanaroff-Riley (FR) type I radio galaxies, onlyone object (10 per cent of the total) was detected in Hi absorption. TheHi absorption in these objects is likely to come from a nuclear disc, asfound for other galaxies of this type (e.g. NGC 4261 and Hydra A). Thelow detection rate is consistent with the hypothesis (as suggested byoptical and X-ray data) that the `standard' parsec-scale, geometricallythick torus is not required in low-luminosity radio galaxies. This isconsistent with earlier optical work. In the case of FR type II powerfulradio galaxies, no Hi absorption has been detected in broad-line radiogalaxies, while three out of four narrow-line radio galaxies have beendetected (the one non-detection having quite a high upper limit). All ofthese are compact or small radio galaxies. To first order this isconsistent with the predictions of the unified schemes, assuming thatthe Hi absorption is caused by an obscuring torus. However, theindications of this being the only cause of the absorption are not verystrong. In particular, we find that in two of the three detected objectsthe Hi is blueshifted compared with the systemic velocity. In the thirdgalaxy (PKS 1549-79) two redshift systems (from the optical lines) arefound. The uncertainty in the systemic velocity derived from opticallines is discussed. Finally, by also considering data available in theliterature, we find a tendency for radio galaxies with a strongcomponent of young stellar population and far-infrared emission to showHi absorption. The overall richer interstellar medium that is likely tobe present in these galaxies may be a factor in producing theabsorption.
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