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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.
|Nearby early-type galaxies with ionized gas. II. Line-strength indices for 18 additional galaxies|
We previously presented a data-set of line-strength indices for 50early-type galaxies in the nearby Universe. The galaxy sample is biasedtoward galaxies showing emission lines, located in environmentscorresponding to a broad range of local galaxy densities, althoughpredominantly in low density environments. The present addendum enlargesthe above data-set of line-strength indices by analyzing 18 additionalearly-type galaxies (three galaxies, NGC 3607, NGC 5077 and NGC 5898were presented in the previous set). We measured 25 line-strengthindices, defined by the Lick IDS "standard" system (Trager et al. 1998,ApJS, 116, 1; Worthey & Ottaviani 1997, ApJS, 111, 377), for 7luminosity weighted apertures and 4 gradients of each galaxy. Thisaddendum presents the line-strength data-set and compares it with theavailable data in the literature.
|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.
|Evolution of smale scale systems of galaxies: X-ray detected E+S galaxy pairs.|
|Tracing Galaxy Evolution in the Field|
|The distribution of atomic gas and dust in nearby galaxies - II. Further matched-resolution Very Large Array H I and SCUBA 850-μm images|
We present Very Large Array (VLA) C-array 21-cm HI images of galaxiesfrom the SCUBA Local Universe Galaxy Survey which have been observed at850 μm with the James Clerk Maxwell Telescope. Matched-resolution (~25 arcsec) HI images of 17 galaxies are presented and compared with850-μm images. HI or 850-μm images of an additional six galaxieswhich were detected at only one wavelength are presented. Additionally,lower resolution H I observations of nine galaxies are presented. Theobservations of these galaxies, along with results previously presented,do not show any obvious trends in the HI/dust or H2/dust massratios with morphological type.
|Emission lines and optical continuum in low-luminosity radio galaxies|
We present spectroscopic observations of a complete subsample of 13low-luminosity radio galaxies selected from the 2-Jy sample of Tadhunteret al. The underlying continuum in these sources was carefully modelledin order to make a much-needed comparison between the emission-line andcontinuum properties of Fanaroff-Riley type Is (FRIs) and those of otherclasses of radio sources. We find that five galaxies in the sample showa measurable ultraviolet (UV) excess: two of these sources are BL Lacs,but in the remaining three galaxies we argue that the most likelycontributor to the UV excess is a young stellar component. Therefore,excluding the BL Lacs, we find that ~30 per cent of the sample showevidence for young stars, which is similar to the results obtained forhigher luminosity samples. We compare our results with far-infraredmeasurements in order to investigate the far-infrared-starburst link.The nature of the optical-radio correlations is investigated in light ofthese new available data and, in contrast to previous studies, we findthat the FRI sources follow the correlations with similar slopes tothose found for the Fanaroff-Riley type IIs. Finally, we compare theluminosities of the emission lines in the FRI and BL Lac sources andfind a significant difference between the [OIII] line luminosities ofthe two groups. Our results are discussed in the context of the unifiedschemes for low-powered radio sources.
|Microwave Interstellar Medium Emission Observed by the Wilkinson Microwave Anisotropy Probe|
We investigate the nature of the diffuse Galactic emission in theWilkinson Microwave Anisotropy Probe (WMAP) temperature anisotropy data.Substantial dust-correlated emission is observed at all WMAPfrequencies, far exceeding the expected thermal dust emission in thelowest frequency channels (23, 33, and 41 GHz). The WMAP team interpretsthis emission as dust-correlated synchrotron radiation, attributing thecorrelation to the natural association of relativistic electronsproduced by supernovae (SNe) with massive star formation in dustyclouds, and deriving an upper limit of 5% on the contribution of Draine& Lazarian spinning dust to the K band (23 GHz). We pursue analternative interpretation that much, perhaps most, of thedust-correlated emission at these frequencies is indeed spinning dust,and explore the spectral dependence on environment by considering a fewspecific objects as well as the full-sky average. Models similar toDraine & Lazarian spinning dust provide a good fit to the full-skydata. The full-sky fit also requires a significant component with a flatspectrum uncorrelated with Hα, possibly hot (~106 K)gas within 30° of the Galactic center.
|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.
|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.
|Line-of-Sight Reddening Predictions: Zero Points, Accuracies, the Interstellar Medium, and the Stellar Populations of Elliptical Galaxies|
Revised (B-V)0-Mg2 data, which are used to testreddening predictions, are presented for 402 elliptical galaxies. Thesereddening predictions can tell us both what the intrinsic errors are inthis relationship among gE galaxy stellar populations as well as detailsof nearby structure in the interstellar medium (ISM) of our Galaxy, andof the intrinsic errors in reddening predictions. Using least-squaresfits, the explicit 1 σ errors in reddenings predicted by theBurstein-Heiles (BH) method and the Schlegel and coworkers (IR) methodare calculated, as well as the 1 σ observational error in the(B-V)0-Mg2 for gE galaxies. It is found that indirections with E(B-V)<0.100 mag (where most of these galaxies lie),1 σ errors in the IR reddening predictions are 0.006-0.009 mag inE(B-V), those for BH reddening predictions are 0.011 mag, and the 1σ agreement between the two reddening predictions is 0.007 mag.The IR predictions have an accuracy of 0.010-0.011 mag in directionswith E(B-V)>=0.100 mag, significantly better than those of the BHpredictions (0.024-0.025). Both methods yield good evidence thatgas-to-dust variations that vary by a factor of 3, both high and low,exist along many lines of sight in our Galaxy. Both methods also predictmany directions with E(B-V)<0.015 mag, despite the difference in zeropoint that each has assumed. The ~0.02 higher reddening zero point inE(B-V) previously determined by Schlegel and coworkers is confirmed,primarily at the Galactic poles. Independent evidence of reddening atthe north Galactic pole (NGP) is reviewed, with the conclusion thatdirections still exist at the NGP that have E(B-V)<<0.01. Twolines of evidence suggest that IR reddenings are overpredicted indirections with high gas-to-dust ratios. As high gas-to-dust directionsin the ISM also include the Galactic poles, this overprediction is thelikely cause of the E(B-V)~0.02 mag larger IR reddening zero pointrelative to that of BH.
|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.
|Jets in the Fanaroff-Riley class I radio galaxies PKS B1234-723, MRC 1452-517 and PKS B2148-555|
We present radio observations made with the Australia Telescope CompactArray to study the jets and lobes of three Fanaroff-Riley class I (FR I)radio galaxies: PKS B1234-723, 1452-517 and B2148-555. The totalintensity and polarization radio images of the FR I jets are used todetermine jet brightness and width variations, magnetic field structureand fractional polarization. The equipartition pressure is determined asa function of distance from the galaxies to probe the intergalacticmedium.
|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.
|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.
|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 (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/757
|Supernovae in isolated galaxies, in pairs and in groups of galaxies|
In order to investigate the influence of environment on supernova (SN)production, we have performed a statistical investigation of the SNediscovered in isolated galaxies, in pairs and in groups of galaxies. 22SNe in 18 isolated galaxies, 48 SNe in 40 galaxy members of 37 pairs and211 SNe in 170 galaxy members of 116 groups have been selected andstudied. We found that the radial distributions of core-collapse SNe ingalaxies located in different environments are similar, and consistentwith those reported by Bartunov, Makarova & Tsvetkov. SNe discoveredin pairs do not favour a particular direction with respect to thecompanion galaxy. Also, the azimuthal distributions inside the hostmembers of galaxy groups are consistent with being isotropics. The factthat SNe are more frequent in the brighter components of the pairs andgroups is expected from the dependence of the SN rates on the galaxyluminosity. There is an indication that the SN rate is higher in galaxypairs compared with that in groups. This can be related to the enhancedstar formation rate in strongly interacting systems. It is concludedthat, with the possible exception of strongly interacting systems, theparent galaxy environment has no direct influence on SN production.
|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.
|A synthesis of data from fundamental plane and surface brightness fluctuation surveys|
We perform a series of comparisons between distance-independentphotometric and spectroscopic properties used in the surface brightnessfluctuation (SBF) and fundamental plane (FP) methods of early-typegalaxy distance estimation. The data are taken from two recent surveys:the SBF Survey of Galaxy Distances and the Streaming Motions of AbellClusters (SMAC) FP survey. We derive a relation between(V-I)0 colour and Mg2 index using nearly 200galaxies and discuss implications for Galactic extinction estimates andearly-type galaxy stellar populations. We find that the reddenings fromSchlegel et al. for galaxies with E(B-V)>~0.2mag appear to beoverestimated by 5-10 per cent, but we do not find significant evidencefor large-scale dipole errors in the extinction map. In comparison withstellar population models having solar elemental abundance ratios, thegalaxies in our sample are generally too blue at a given Mg2;we ascribe this to the well-known enhancement of the α-elements inluminous early-type galaxies. We confirm a tight relation betweenstellar velocity dispersion σ and the SBF `fluctuation count'parameter N, which is a luminosity-weighted measure of the total numberof stars in a galaxy. The correlation between N and σ is eventighter than that between Mg2 and σ. Finally, we deriveFP photometric parameters for 280 galaxies from the SBF survey data set.Comparisons with external sources allow us to estimate the errors onthese parameters and derive the correction necessary to bring them on tothe SMAC system. The data are used in a forthcoming paper, whichcompares the distances derived from the FP and SBF methods.
|The radio galaxy Centaurus B|
Centaurus B (PKS B1343-601) is one of the brightest and closest radiogalaxies, with flux density ~250Jy at 408MHz and redshift 0.01215, butit has not been studied much because of its position (i) close to theGalactic plane (it is also known as G309.6+1.7 and Kes 19) and (ii) inthe southern sky. It has recently been suggested as the centre of ahighly obscured cluster behind the Galactic plane. We present radioobservations made with the Australia Telescope Compact Array andMolonglo Observatory Synthesis Telescope to study the jets and lobes.The total intensity and polarization radio images of the FR I jets areused to determine the jet brightness and width variations, magneticfield structure and fractional polarization. The equipartition pressurecalculated along the jets declines rapidly over the first 1arcmin fromthe galaxy reaching a constant pressure of10-13h-4/7 Pa in the lobes blown in theintracluster medium.
|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.
|The LX-σ Relation for Galaxies and Clusters of Galaxies|
We demonstrate that individual elliptical galaxies and clusters ofgalaxies form a continuous X-ray luminosity-velocity dispersion(LX-σ) relation. Our samples of 280 clusters and 57galaxies have LX~σ4.4 andLX~σ10, respectively. This unifiedLX-σ relation spans 8 orders of magnitude inLX and is fully consistent with the observed and theoreticalluminosity-temperature scaling laws. Our results support the notion thatgalaxies and clusters of galaxies are the luminous tracers of similardark matter halos.
|New Evidence for the Unified Scheme of BL Lacertae Objects and FR I Radio Galaxies|
In this paper, we collect radio and X-ray observations for mostFanaroff-Riley I (FR I) radio galaxies in the Zirbel-Baum radio galaxysample and investigate the distribution of the radio-to-X-ray effectivespectral index, αrx, to test the unified scheme of BLLac objects and FR I radio galaxies. It is found that the range ofαrx for FR I radio galaxies is almost the same as thatfor BL Lac objects, that the distribution of αrxprobably peaks at the same position as BL Lac objects, and that thedistribution of αrx for FR I galaxies is similar tothat for BL Lac objects. These suggest that there exist two subclassesof FR I radio galaxies: one is HBL-like, and the other is LBL-like,corresponding to high-energy-peaked (HBL) and low-energy-peaked (LBL) BLLac objects, respectively. This result is consistent with previous VLAobservations and supports the unified scheme of BL Lac objects and FR Iradio galaxies.
|ROSAT-HRI observations of six southern galaxy pairs|
We present the detailed analysis of the X-ray data for 6 pairs, isolatedor in poor groups, observed at high resolution with the ROSAT HRI . Inall cases, the stronger X-ray source is associated with the brighterearly-type member and is extended. The extent varies from galactic togroup scale, from 3 (RR 210b) to 182 kpc( RR 22a). The fainter membersare detected only in two pairs, RR 210 and RR 259. Except for one case,no significant substructures have been detected in the X-ray maps,possibly also as a consequence of the poor statistics. The core radii ofthe X-ray surface brightness profiles are in the range 1-3 kpc. Thedistribution of the luminosities of galaxies in pairs encompasses a verywide range of both luminosities and LX / LBratios, in spite of the very small number of objects studied so far. Ourdata provide no evidence that pair membership affects the X-rayproperties of galaxies. Observation are discussed in the context of thepair/group evolution.
|Seeing Galaxies through Thick and Thin. I. Optical Opacity Measures in Overlapping Galaxies|
We describe the use of partially overlapping galaxies to provide directmeasurements of the effective absorption in galaxy disks, independent ofassumptions about internal disk structure. The nonoverlapping parts ofthe galaxies and symmetry considerations are used to reconstruct, viadifferential photometry, how much background galaxy light is lost inpassing through the foreground disks. Extensive catalog searches andfollow-up imaging yield ~15-25 nearby galaxy pairs suitable for varyingdegrees of our analysis; 11 of the best such examples are presentedhere. From these pairs, we find that interarm extinction is modest,declining from AB~1 mag at 0.3RB25 toessentially zero by RB25; the interarm dust has ascale length consistent with that of the disk starlight. In contrast,dust in spiral arms and resonance rings may be optically thick(AB>2) at virtually any radius. Some disks have flatterextinction curves than the Galaxy, with AB/AI~1.6this is probably the signature of clumpy dust distributions. Even thoughtypical spirals are not optically thick throughout their disks, wherethey are optically thick is correlated with where they are mostluminous: in spiral arms and inner disks. This correlation betweenabsorption and emission regions may account for their apparent surfacebrightness being only mildly dependent on inclination, erroneouslyindicating that spirals are generally optically thick. Taken as anensemble, the opacities of spiral galaxies may be just great enough tosignificantly affect QSO counts, though not enough to cause theirhigh-redshift cutoff. Based in part on archival observations with theNASA/ESA Hubble Space Telescope (HST) obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS5-26555.
|Optical surface photometry of radio galaxies. II. Observations and data analysis|
Optical imaging observations for 50 radio galaxies are presented. Foreach object isophotal contours, photometric profiles, structuralparameters (position angle, ellipticity, Fourier coefficients), andtotal magnitudes are given. These observations, obtained in the CousinsR band, complement the data presented in a previous paper and are partof a larger project aimed at studying the optical properties of lowredshift (z<= 0.12) radio galaxies (Govoni et al. 1999). Comments foreach individual source are reported.
|Parsec-scale structures of radio galaxies in the 2-Jy sample|
In this paper we present the results of VLBI observations of six radiogalaxies belonging to the 2-Jy sample. The selected objects are 3C17,PKS 0620-52, PKS 0625-35, PKS 1318-43, PKS 1333-33 and 3C317. The firstis a high power radio galaxy and the remainder are all low powerobjects. Our observations were carried out with a set of differentarrays and frequencies, and cover a range of resolutions from a few masto a few tens of mas. Parsec-scale images are presented and discussed inthe light of unification for radio loud galaxies. Estimates for theintrinsic plasma speeds in these objects in the proximity of theparsec-scale core and their orientation to the line of sight are inagreement with the predictions from unified models and with theiroptical and X-ray properties. We will use H_o = 50 kms-1Mpc-1, q_o = 0 and S ~ nu -alpha throughout the paper.
|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.
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