|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
|The optical/near-IR colours of red quasars|
We present quasi-simultaneous multi-colour optical/near-IR photometryfor 157 radio selected quasars, forming an unbiassed sub- sample of theParkes Flat-Spectrum Sample. Data are also presented for 12 opticallyselected QSOs, drawn from the Large Bright QSO Survey. The spectralenergy distributions of the radio- and optically-selected sources arequite different. The optically selected QSOs are all very similar: theyhave blue spectral energy distributions curving downwards at shorterwavelengths. Roughly 90% of the radio-selected quasars have roughlypower-law spectral energy distributions, with slopes ranging fromFν ∝ ν0 to Fν ∝ν-2. The remaining 10% have spectral energy distributionsshowing sharp peaks: these are radio galaxies and highly reddenedquasars. Four radio sources were not detected down to magnitude limitsof H ~ 19.6. These are probably high redshift (z >3) galaxies orquasars. We show that the colours of our red quasars lie close to thestellar locus in the optical: they will be hard to identify in surveyssuch as the Sloan Digital Sky Survey. If near-IR photometry is added,however, the red power-law sources can be clearly separated from thestellar locus: IR surveys such as 2MASS should be capable of findingthese sources on the basis of their excess flux in the K-band.
|X-ray properties of the Parkes sample of flat-spectrum radio sources: dust in radio-loud quasars?|
We investigate the X-ray properties of the Parkes sample offlat-spectrum radio sources using data from the ROSAT All-Sky Survey andarchival pointed PSPC observations. In total, 163 of the 323 sources aredetected. For the remaining 160 sources, 2sigma upper limits to theX-ray flux are derived. We present power-law photon indices in the0.1-2.4 keV energy band for 115 sources, which were determined eitherwith a hardness ratio technique or from direct fits to pointed PSPC dataif a sufficient number of photons were available. The average photonindex is =1.95^+0.13_-0.12 for flat-spectrum radio-loudquasars, =1.70^+0.23_-0.24 for galaxies, and=2.40^+0.12_-0.31 for BL Lac objects. The soft X-ray photonindex is correlated with redshift and with radio spectral index in thesense that sources at high redshift and/or with flat (or inverted) radiospectra have flatter X-ray spectra on average. The results are in accordwith orientation-dependent unification schemes for radio-loud activegalactic nuclei. Webster et al. discovered many sources with unusuallyred optical continua among the quasars of this sample, and interpretedthis result in terms of extinction by dust. Although the X-ray spectrain general do not show excess absorption, we find that low-redshiftoptically red quasars have significantly lower soft X-ray luminositieson average than objects with blue optical continua. The differencedisappears for higher redshifts, as is expected for intrinsic absorptionby cold gas associated with the dust. In addition, the scatter in log(f_x/f_o) is consistent with the observed optical extinction, contraryto previous claims based on optically or X-ray selected samples.Although alternative explanations for the red optical continua cannot beexcluded with the present X-ray data, we note that the observed X-rayproperties are consistent with the idea that dust plays an importantrole in some of the radio-loud quasars with red optical continua.
|The Parkes Half-Jansky Flat-Spectrum Sample|
We present a new sample of Parkes half-jansky flat-spectrum radiosources, having made a particular effort to find any previouslyunidentified sources. The sample contains 323 sources selected accordingto a flux limit of 0.5Jy at 2.7GHz, a spectral index measured between2.7 and 5.0GHz of alpha_2.7/5.0>-0.5, where S(nu)~nu ^alpha, Galacticlatitude |b|>20 deg and -45 deg< declination (B1950) <+10 deg.The sample was selected from a region 3.90 steradians in area. We haveobtained accurate radio positions for all the unresolved sources in thissample, and combined these with accurate optical positions fromdigitized photographic sky survey data to check all the opticalidentifications. We report new identifications based on R- and Kn-bandimaging and new spectroscopic measurements of many of the sources. Wepresent a catalogue of the 323 sources, of which 321 now have identifiedoptical counterparts and 277 have measured spectral redshifts.
|An image database. II. Catalogue between δ=-30deg and δ=70deg.|
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
|CCD calibration of the magnitude scale for the SSRS2 sample: The equatorial region|
In this paper we continue our investigation on the isophotal nature,accuracy, and uniformity of the magnitude system adopted in the SouthernSky Redshift Survey extension (SSRS2). Extending our earlier work, weexamine galaxies in the equatorial region, primarily in the declinationrange delta greater than or equal to -17.5 deg and less than or equal to0 deg, over a large range of right ascension, covering the southern andnorthern Galactic caps. For this purpose, we have obtained CCD isophotalmagnitudes in the B and R bands for 265 galaxies of differentmorphological types. Using the larger sample we confirm our earlierclaim that the mSSRS2 magnitudes are very nearly themagnitude measured within the isophote muB = 26 mag/sqarcsec, with a dispersion of about 0.30 mag. The relative zero-pointoffset between our mSSRS2 magnitudes and the CCD photometryis -0.02 mag from all data we have obtained. However, we detect avariation of the zero-point across different regions of the sky of +/-0.10 mag for regions at large angular separations. We also estimate thatthe zero-point offset between the mSSRS2 and Zwicky systemsis relatively small (approximately 0.10 mag), which should allow us tocombine the data from the SSRS2 and the CfA2 Redshift Survey.
|A Survey of 526 Soutern Flat Spectrum Radio Sources with the Parkes / Tidbinbilla Interferometer|
|On the redshift-apparent size diagram of double radio sources|
We review the data on the angular sizes of double radio sources. Thereis a positive correlation between the true radio source size and radiopower among low-luminosity radio galaxies. This may be partly explainedthrough sample selection effects. There is a negative correlationbetween radio size and power among high luminosity radio galaxies andall quasars. It follows the constant total energy envelope closely.There is no significant difference between the radio sizes of radiogalaxies and quasars of the same luminosity. However, it is possiblethat real differences in the radio sizes of the two populations arehidden by selection effects in our sample. The angular size-redshiftdiagram shows a deficiency of large radio sources at high redshiftswhich is fully explained by the above-mentioned negative correlationwithout need for cosmic evolution of radio source size. However, thepossibility of some cosmic evolution is not totally ruled out by thedata.
|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.
|The cluster environments of powerful radio galaxies|
Results in the form of the ratio of the spatial cross-correlationamplitude to the autocorrelation amplitude are given as estimates of thelocal galaxy density around about 200 powerful radio sources. Lickgalaxy counts for z of less than 0.1 are extended to z of less than 0.25using deep galaxy samples from UK Schmidt plates. Although thelow-luminosity Fanaroff-Riley class I sources lie in richer clustersthan those of class II, a real scatter in properties is found. Theresults show no statistical evidence for the difference in environmentsuggested to exist between different subclasses of the class II sources.Compact radio sources are found to lie in regions of low galacticdensity.
|A VLBI survey at 2.29 GHz|
VLBI observations at 2.29 GHz with fringe spacings of about 3milliarcsec have been performed on 1398 radio sources spread over theentire sky. 917 sources were detected, including 93 percent of theidentified BL Lacertae objects, 86 percent of the quasars, and 36percent of the galaxies. The resulting catalog of compact radio sourcesis useful for various astrophysical studies and in the formation of VLBIcelestial reference frames.
|A correlation between ellipticity and core-strength in extended radio galaxies|
It is shown that in the case of extended radio sources a correlationexists between the fraction of the radio flux retained in the corecomponent and the ellipticity of the underlying galaxy. The correlationis in the sense that stronger cores occur in flatter galaxies. It wouldseem that there exists a class of intrinsically rounder, redder, massiveellipticals with larger velocity dispersions and metallicities, that canform extended radio sources more efficiently. Thus the occurrence of aradio source appears to be related to the dynamical and chemicalevolution of the Galaxy.
|Very Long Baseline Interferometry observations of 257 extragalactic radio sources in the ecliptic region|
Very Long Baseline Interferometry observations of 257 extragalacticradio sources with 10 deg of the ecliptic have been conducted at afrequency of 2.29 GHz. Compact components with flux densities greaterthan 0.1 Jy and angular sizes smaller than the fringe spacings of 2.5and 3.2 milliarsec were detected in 144 radio sources. This survey wasconducted to find compact radio sources to form a high accuracyreference frame for planetary spacecraft navigation. This stablereference frame may also be useful for long-term studies of planetarydynamics.
|Relative orientations of the axes of radio sources and the elliptical galaxies associated with them|
A study is made of the relationship between the major axes of radiogalaxies and the elliptical galaxies associated with them. It is foundthat if the ratio of the major axes of the radio galaxies to thediameters of the radio components is greater than 2.5 there is a clearcorrelation between the directions of the major axes of the radiogalaxies and the minor axes of the optical galaxies. But if the ratio isless than 2.5, then the directions of the major axes of the radio andthe optical galaxies are well correlated. This result agrees well with amechanism of formation of radio galaxies in which it is assumed thatthey are formed from clouds of relativistic particles that are ejectedfrom the central regions of the elliptical galaxies and move in thedipole magnetic field of these galaxies.
|Are there correlations between radio and optical axes of radio galaxies|
The relative orientations of radio and optical axes of radio galaxieshave been examined on the basis of combined material from several smallsamples. Rotation axes of some radio galaxies have been redeterminedassuming that the published measurements refer to rotational motionsonly. It is found that the rotation axis is quite different from thoseprevious determinations, where rotation-expansion models were used. Inparticular, the correlation between radio source axes and rotation axesdisappears when the allowance for expansion is dropped. No statisticallysignificant correlation between optical major axes of the galaxay imageand radio source axes is found when all existing measurements, notexceeding 140, are combined.
|Comparisons of the orientations of double-lobed radio sources and their associated elliptical galaxies|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1981ApJ...243..427W&db_key=AST
|Extended radio sources and elliptical galaxies. II. A search for radio cores using the VLA.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978AJ.....83..725F&db_key=AST
|The Ohio Survey between 0 and -36 degrees .|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75..351E&db_key=AST
|The Parkes catalogue of radio sources, declination zone 0° to -20°|
|Accurate positions of 644 radio sources|