Upload your image
DSS Images Other Images
Submit a new article
|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.
|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.
|Spectral Indices of Core and Extended Components of Extragalactic Radio Sources|
We use observed peak and total flux densities at 6 cm and 20 cm todetermine the spectral indices separately for the core and extendedcomponents of QSOs and galaxies, as well as their core-dominanceparameters. Our results indicate that 1) Nine QSOs show both greaterthan 1.0 core-dominance parameters (those objects should be blazars) andgreater than 0.5 spectral indices. The average core spectral index isαCore = 0.85±0.21 for the nine blazars, whichimplies that it is not reliable to use αradio=0.0 forblazars. For the different subclasses, the core andextended spectralindices are as follows: for the blazars, αCore =0.22±0.06 and αExt =0.77±0.12; the galaxies,αCore = 1.01±0.13 and αExt=0.83±0.21, and for the QSOs, αCore = 0.28±0.10and αExt =0.68±0.08. 2) The core spectral index andcore dominance parameter (R) show an anti-correlation,αC = (-1.28±0.26) log R +(0.65±0.11); 3) R isapproximately linearly correlated with redshift (z).}
|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.
|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.
|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.
|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.
|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.
|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.
|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.
|A 98 per cent spectroscopically complete sample of the most powerful equatorial radio sources at 408MHz|
A new sample of very powerful radio galaxies is defined from theMolonglo Reference Catalogue, according to the criteriaS408MHz>5Jy, -30 deg<=δ<=10 deg and |b|>=10deg. The sample is selected to have similar properties to the northern3CR revised sample, and to be visible to a combination of existingnorthern telescopes such as the Very Large Array radio interferometerand large southern hemisphere telescope facilities. The sample contains178 sources, of which spectroscopic redshifts are available in theliterature for 128. For the remaining 50 sources, new radio imaging,optical imaging and spectroscopic observations are presented to identifythe host galaxies and determine their redshifts. With these newobservations the total sample is 100per cent optically identified andredshifts are available for 174 (98per cent) of the sources. The sampleconsists of one starburst galaxy, one Seyfert galaxy, 127 radio galaxiesand 49 quasars. Basic properties of the sample, such as thedistributions of the quasar and radio-galaxy populations in redshift andtheir locations on the radio power versus linear size (P-D) diagram,show no significant differences from the revised 3CR sample. Theequatorial location and the high spectroscopic completeness of thissample make it a valuable resource for detailed studies of the natureand environments of these important objects with the new generation ofsouthern hemisphere telescopes.
|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).
|The radio structures of southern 2-Jy radio sources: New ATCA and VLA radio images|
We present new radio images obtained with the Australia TelescopeCompact Array (ATCA) and the Very Large Array (VLA) for a group of 14galaxies belonging to the 2-Jy sample of radio sources. The new imagesimprove the data already available on these objects and, in general, thedatabase that we are building up on the sample. They will also be usedfor follow-up work where radio-optical comparison will be done. Webriefly discuss the core dominance parameter (R) for the objects forwhich the new data have given new information and, in particular, forbroad line radio galaxies (BLRG). One of the BLRG does not show a core,even at 3 cm, and this is at variance with the general tendency of BLRGto have relatively strong cores. The depolarization is also discussedfor a group of small double-lobed radio galaxies.
|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.
|The Molonglo Reference Catalog 1 Jy Radio Source Survey. II. Radio Structures of Galaxy Identifications|
This is the second in a series of papers discussing the radio, optical,and near-IR properties of a large and complete sample of radio sourcesselected from the Molonglo Reference Catalog (MRC) at 408 MHz. Thesample consists of 557 radio sources from the MRC that have S_0.408>= 0.95 Jy, -30 deg < delta < -20 deg, and |b| >= 20 deg butexcluding the right ascension range of 14^h03^m-20^h20^m. While 111 ofthese are identified with quasars (including six with BL Lac objects), avast majority of the rest are identified with galaxies. Only a smallfraction (<~2%) appear to have no optical or near-IR counterpartsdown to an r magnitude of ~24 or a K magnitude of ~19. A similarfraction have ambiguous identifications. This paper presents the radiostructures of the 446 radio sources in the sample that are eitheridentified with galaxies or that have remained unidentified. Most of thestructural information given in the paper is based on high-resolution(~1"-10") observations made with the Very Large Array at a frequency of4.86 GHz. Several of the large or diffuse sources were also observed at1.41 GHz. Contour plots of the radio images are also presented for thewell-resolved sources. A substantial fraction (~20%) of the sources inthe galaxy sample is found to be of the ``compact steep spectrum''variety with alpha^4.86_0.408>0.5 and linear size l <~ 20 kpc (forH_0 = 50 km s^-1 Mpc^-1 q_0 = 0.5).
|Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies|
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
|A study of cores in a complete sample of radio sources|
The high resolution provided by the Parkes-Tidbinbilla real-timeinterferometer (PTI) has been used to measure the core flux density fora complete sample of radio sources. Lower resolution maps are alreadyavailable for most of these objects together with optical(spectroscopic) data. The new data show that an inverted spectral indexalpha~-0.3 (S~nu^-alpha) could be characteristic of all the nuclei,going from low-luminosity radio galaxies to powerful quasars. Takingthis spectral index into account, the measured flux density does notchange very much, going from a scale of tens of kpc (corresponding tothe low-resolution observations) to the sub-kpc scale of the newobservations. Thus, most of the flux observed in the central regionoriginates in a sub-kpc area. With the new PTI data we obtain a betterestimate of the radio core dominance (R), i.e. the ratio between thecore and the extended radio flux. This parameter is claimed to be a goodindicator of the orientation of the beamed radiation with respect to theline of sight, and hence a very important parameter for testing `unifiedschemes' for active galactic nuclei (AGN). Using this parameter,together with optical spectroscopic information, we find that the radiocore dominance shows different distributions for different radio andoptical characteristics. A statistically significant difference in thedistribution of R is observed between Fanaroff-Riley (FR) I and FR IIradio galaxies, supporting the idea that low-power sources are lessaffected by beaming because they have, on average, a lower Lorentzfactor. Among the FR II radio galaxies, narrow-line radio galaxies(NLRGs) show lower values of R while the broad-line radio galaxies(BLRGs) have the largest R. Moreover, the median value of R for BLRGs islower than for steep-spectrum quasars (SSQ) even after a number ofselection effects are taken into account. This result can be explainedin the framework of unified schemes for AGN assuming that in the BLRGswe are seeing more directly into the nucleus, although not as much as inSSQs.
|The soft X-ray properties of a complete sample of radio sources.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996MNRAS.279.1331S&db_key=AST
|The Molonglo Reference Catalog/1 Jansky Radio Source Survey. I. Radio Galaxy Identifications|
This is the first in a series of papers discussing the properties of acomplete set of radio sources selected near S_408_ = 1 Jy. We presentoptical or infrared identifications for a sample of 452 radio galaxies.The sources were selected from the 408 MHz Molonglo Reference Catalog,restricted only by flux density and position on the sky, as follows:S_408_ >= 0.95 Jy and -30^deg^ < decl. (1950) <-20^deg^, and9^h^20^m^ < R.A.(1950) < 14^h^4^m^ or 20^h^20^m^ < R.A.(1950)< 6^h^14^m^. This complete sample, the MRC/1 Jy survey, contains 558radio galaxies or quasars, of which six are occulted by bright stars orgalaxies and two are multiple confused sources. Of the remaining 550sources, 527, or 96%, are identified to an r magnitude of 25, and eightadditional sources are identified to K = 19. Of the 17 unoccultedobjects that remain unidentified, 15 are sources for which we haveeither poor radio maps or inadequate optical/IR images. This paperpresents finding charts and astrometric positions for the 452 sourcesthat are not identified as either quasars or BL Lacertae objects.Magnitudes in the r passband accurate to typically 0.1 mag are given for353 of the radio galaxy identifications. Redshifts for 268 of thegalaxies are also listed; these have been derived from 450 spectroscopicobservations. The radio observations, quasar and BL Lac identifications,spectroscopy, and near- IR images will be presented in subsequent papersin this series.
|Candidates for a southern extension of the Karachentsev catalogue of isolated pairs of galaxies.|
|Parsecscale Radio Cores in Early Type Galaxies|
We find compact (<0.03 arcsec) radio-continuum cores in about 70 percent of radio-emitting elliptical and S0 galaxies over a wide range intotal radio power (10^21^-,10^26^ W Hz^-1^ at 5 GHz). The cores usuallyhave a flat or rising spectrum between 2.3 and 8.4 GHz, with a medianspectral index of + 0.3. Even at low luminosities, the radio emissionfrom most elliptical galaxies appears to be powered by a parsec-scale`engine' like those in classical radio galaxies and quasars. The coreand total radio power are related (P_core_ is proportional toP_total_^0.7^ on average), and the parsec-scale cores of radio galaxiesare typically one hundred times more powerful than those in `normal'giant elliptical galaxies.
|The optical identification status of the 1 Jy radio source catalogue|
Optical identifications, magnitudes, redshifts, and polarization datahave been gathered from an extensive literature search to form an updateof the optical data for the radio sources of the 1 Jy catalogue. Of the527 radio sources in the revised catalogue, 97% have opticalcounterparts, and redshifts are given for 90% of the opticallyidentified sources. For all but a few sources, accurate interferometerradio position are provided. References are made to well knowncompilations as well as to individual papers, often supplemented byspecial notes on individual objects.
|The Radio Structures of Southern 2-JY Radio Sources|
A subsample of the Wall & Peacock 2-Jy sample of radio sources, withredshift z < 0.7 or unknown and declination δ < + 10^deg^,has been selected and observed in the radio at 6 cm (or information wasobtained from the literature where appropriate) and in the optical withlow- dispersion spectroscopy. Here we present the new radio data. Weobserved 66 sources with the Very Large Array and seven southern sourceswith the Australia Telescope Compact Array. Together with the datacollected from the literature, we now have information about the radiostructure of 107 sources. These data will be discussed along withoptical spectra for the sample in a future paper.
|Optical Spectroscopy of a Complete Sample of Southern 2-JY Radio Sources|
We present optical spectra for a complete sample of radio galaxies andquasars comprising all sources from the Wall & Peacock 2.7-GHzsample with redshifts z < 0.7 and declinations δ < +10^deg^; this sample is complete down to a flux density of 2 Jy.Although not all of the 2-Jy sources have spectroscopic redshifts, weargue that most of the unidentified objects are at high redshifts andthat our z < 0.7 sample is largely complete. The optical data will beanalysed in a future paper.
|The large-scale clustering of radio galaxies|
An all-sky sample of radio galaxies at redshifts equal to or less than0.1 is used to study clustering in the universe on scales up to severalhundred Mpc. The two-point correlation function for these galaxies isconsistent with their high optical luminosity and location in moderatelyrich environment. Direct methods for obtaining the power spectrum of thedensity field traced by the radio galaxies are discussed taking intoaccount the selection function of the sample. The results of thepower-spectrum analysis indicate that the distribution of radio galaxiesis more uniform on very large scales than would be predicted from anextrapolation of the power-law clustering found on small scales.
|Flux densities at 8400 MHz for a large sample of radio sources|
This paper presents 8400-MHz flux densities for 1194 southern radiosources. The sources were selected from the Parkes 2700-MHz Survey toinclude all those stronger than 0.5 Jy at that survey's findingfrequency of 2700 MHz. The new fluxes have an accuracy of about 8percent, corresponding to 0.05 Jy for a typical source. It isanticipated that the data will be useful in defining the high-frequencyradio spectra of many sources as well as in pinpointing objects withwhich to improve the southern, astrometric absolute reference frame.
|Detection of excess rotation measure due to intracluster magnetic fields in clusters of galaxies|
The Faraday rotation measures of a sample of extragalactic radio sourcesprojected within a third of an Abell radius of a galaxy cluster werecompared with those of sources located further from cluster centers. Theresult strongly indicates that the distribution of the residual rotationmeasure (RRM) in the former population is broadened, at a confidencelevel exceeding 99 percent. The broadening is detectable out to1/h50 Mpc. The best present estimate of the excess Faradayrotation measure varies from 100 + or - 36 rad/sq m in the central sixthof an Abell radius to 36 + or - 15 rad/sq m further out. The combinationof these results with electron densities determined from X-ray data forsome of the clusters suggests that magnetic field strengths in clustergas are of order 1 microgauss.
|Radio spectra of quasars. II|
The second part of a search at 1410 MHz for 230 extragalactic objectsfrom the Southern Hemisphere identified as quasars and listed byVeron-Cetty and Veron (1983) is presented. The 30-m radiotelescope ofthe Instituto Argentino de Radioastronomia (IAR) was used. Fromobservations at different frequencies, the index and curvature of thecorresponding spectra were calculated. The 230 quasars cover a sky areafrom 06 h to 16 h 40 m in right ascension and from -9.5 to -90 deg indeclination. All of them are part of a complete sample of 700 quasars.
Submit a new link
Member of following groups:
Observation and Astrometry data
Catalogs and designations: