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|Hubble Space Telescope Imaging of Brightest Cluster Galaxies|
We used the Hubble Space Telescope Wide Field Planetary Camera 2 toobtain I-band images of the centers of 81 brightest cluster galaxies(BCGs), drawn from a volume-limited sample of nearby BCGs. The imagesshow a rich variety of morphological features, including multiple ordouble nuclei, dust, stellar disks, point-source nuclei, and centralsurface brightness depressions. High-resolution surface brightnessprofiles could be inferred for 60 galaxies. Of those, 88% havewell-resolved cores. The relationship between core size and galaxyluminosity for BCGs is indistinguishable from that of Faber et al.(published in 1997, hereafter F97) for galaxies within the sameluminosity range. However, the core sizes of the most luminous BCGs fallbelow the extrapolation of the F97 relationshiprb~L1.15V. A shallower relationship,rb~L0.72V, fits both the BCGs and thecore galaxies presented in F97. Twelve percent of the BCG sample lacks awell-resolved core; all but one of these BCGs have ``power law''profiles. Some of these galaxies have higher luminosities than anypower-law galaxy identified by F97 and have physical upper limits onrb well below the values observed for core galaxies of thesame luminosity. These results support the idea that the centralstructure of early-type galaxies is bimodal in its physical propertiesbut also suggest that there exist high-luminosity galaxies withpower-law profiles (or unusually small cores). The BCGs in the lattercategory tend to fall at the low end of the BCG luminosity function andtend to have low values of the quantity α (the logarithmic slopeof the metric luminosity as a function of radius, at 10 kpc). Sincetheoretical calculations have shown that the luminosities andα-values of BCGs grow with time as a result of accretion, thissuggests a scenario in which elliptical galaxies evolve from power-lawprofiles to core profiles through accretion and merging. This isconsistent with theoretical scenarios that invoke the formation ofmassive black hole binaries during merger events. More generally, theprevalence of large cores in the great majority of BCGs, which arelikely to have experienced several generations of galaxy merging,underscores the role of a mechanism that creates and preserves cores insuch merging events.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS 5-26555. These observations are associated withproposal 8683.
|Magnetic Energy of the Intergalactic Medium from Galactic Black Holes|
We present a quantitative analysis of two radio source samples havingopposite extremes of ambient gas density that leads to important newconclusions about the magnetic energy in the intergalactic medium (IGM).We analyze here (1) a new, large sample of well-imaged ``giant''extragalactic radio sources that are found in rarefied IGM environmentsand (2) at the other extreme, radio galaxies situated in the densestknown IGM environments, within 150 kpc of rich cluster cores. We findthat sources in the former sample contain magnetic energiesEB~1060-1061 ergs and could be viewedas important ``calorimeters'' of the minimum energy a black hole (BH)accretion disk system injects into the IGM. In contrast to the radiationenergy released by BH accretion, most of the magnetic energy is``trapped'' initially in a volume, up to ~1073cm3, around the host galaxy. But since these large,megaparsec-scale radio lobes are still overpressured after the activegalactic nucleus phase (AGN), their subsequent expansion and diffusionwill magnetize a large fraction of the entire IGM. This suggests thatthe energy stored in intergalactic magnetic fields will have a major, asyet underestimated effect on the evolution of subsequently forminggalaxies. Comparison with the second, cluster core-embedded sample showsthat the minimum magnetic energy EB can be a stronglyvariable fraction of the inferred accretion energy Eacc, andthat it depends on the ambient IGM environment. Cluster embedded AGNsinject significant energy as PdV work on the thermal ICM gas, and theirmagnetic energy, even ignoring the contribution from stellar andstarburst outflows, is sufficient to account for that recently foundbeyond the inner cores of galaxy clusters. We discuss the various energyloss processes as these magnetized CR clouds (lobes) undergo theirenormous expansion into the IGM. We conclude that the aggregate IGMmagnetic energy derived purely from galactic black holes since the firstepoch of significant galaxy BH formation is sufficiently large that itwill have an important influence on the process of both galaxy andvisible structure formation on scales up to ~1 Mpc.
|Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies|
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
|The Deep X-Ray Radio Blazar Survey. I. Methods and First Results|
We have undertaken a survey, the Deep X-Ray Radio Blazar Survey (DXRBS),of archived, pointed ROSAT Position Sensitive Proportional Counter datafor blazars by correlating the ROSAT WGACAT database with severalpublicly available radio catalogs, restricting our candidate list toserendipitous flat radio spectrum sources (alpha_r <= 0.70, whereS_nu ~ nu^-alpha_r . We discuss our survey methods, identificationprocedure, and first results. Our survey is found to be ~95% efficientat finding flat-spectrum radio-loud quasars (FSRQs; 59 of our first 85identifications) and BL Lacertae objects (22 of our first 85identifications), a figure that is comparable to or greater than thatachieved by other radio and X-ray survey techniques. The identificationspresented here show that all previous samples of blazars (even whentaken together) did not representatively survey the blazar population,missing critical regions of (L_X, L_R) parameter space within whichlarge fractions of the blazar population lie. Particularly important isthe identification of a large population of FSRQs (>~25% of DXRBSFSRQs) with ratios of X-ray to radio luminosity >~10^-6 (alpha_rx<~ 0.78). In addition, as a result of our greater sensitivity, theDXRBS has already more than doubled the number of FSRQs in completesamples with 5 GHz (radio) luminosities between 10^31.5 and 10^33.5 ergss^-1 Hz^-1, and fills in the region of parameter space betweenX-ray-selected and radio-selected samples of BL Lac objects. The DXRBSis the very first sample to contain statistically significant numbers ofblazars at low luminosities, approaching what should be the lower end ofthe FSRQ luminosity function. Based on observations collected at theEuropean Southern Observatory, La Silla, Chile; Kitt Peak NationalObservatory; Cerro Tololo Inter-American Observatory; and the AustraliaTelescope National Facility.
|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.
|Properties of nearby clusters of galaxies. III. A 76, A 157, A 407, A 505, A 671, A 779, A 1700, A 2028, A 2040, A 2052 A 2063, A 2065, A 2593, A 2657, A 2670|
We present F band photometry, from digitized 48-inch Palomar plates, of2818 galaxies brighter than m_3+3 in 15 Abell clusters. For each galaxy,absolute coordinates, magnitude, size, ellipticity and orientation aregiven. For each cluster we provide finding charts and contour maps ofthe galaxy surface density. The absolute coordinates of the galaxies ofother 8 clusters presented in the first paper of this series are alsoincluded.
|Classical Double Radio Galaxies and Their Gaseous Environments|
A sample of classical double radio galaxies has been constructed tostudy the effect of environment on radio sources. The sample consists ofradio galaxies in cluster and noncluster environments and includesgalaxies and clusters at both high (z ~ 0.5) and low (z ~ 0) redshift.Most of these radio galaxies are intermediate-power FR II sources with408 MHz powers in the range from 10^32^ to 10^35^ h^-2^ ergs s^-1^ Hz^-1^, where the upper bound corresponds roughly to a 178 MHz power ofabout 10^27^ h^-2^ W Hz^-1^ sr^-1^. Comparisons are made between theproperties of FR II radio galaxies in cluster and nonclusterenvironments, and between X-ray clusters with and without FR II radiogalaxies. The principal results are the following: 1. Most low-redshiftFR II galaxies in clusters appear to be similar to FR II galaxies ingroup or field environments in terms of radio power, optical propertiesof the host galaxy, and nonthermal pressure of the radio bridge. 2.High-redshift FR II galaxies are all quite similar and do not appear tovary with galactic environment. The radio powers and emission- lineluminosities of the host galaxies of high-redshift FR II sources arehigher on average than their low-redshift counterparts, but there isalso overlap, and the nonthermal pressures of the radio bridges appearto be independent of redshift. 3. The nonthermal pressures of thebridges of FR II sources appear to be similar to the thermal pressuresof the ICM around them. This result, if confirmed by a larger sample,would allow the bridges of FR II sources to be used as probes of theirgaseous environments. 4. The fact that most FR II galaxies have similarnonthermal pressures, irrespective of galactic environment and redshift,indicates that the gaseous environments around them are also similar.Typical nonthermal pressures of these FR II sources are much lower thantypical thermal pressures of the ICM in X-ray bright clusters,suggesting that FR II sources are generally in environments with gaspressures much less than typical low-redshift ICM pressures. 5. X-raydata at low redshift show that clusters with FR II sources tend to beunderluminous in the X-ray compared to clusters without FR II sources.This suggests that the ICM pressures in these clusters are relativelylow, consistent with the results obtained from the analysis of thenonthermal pressures of FR II sources. 6. Unfortunately, the X-ray datafor high-redshift clusters with FR II sources are inconclusive becauseof the large number of upper bounds involved and possible AGNcontribution to the X-ray luminosity. However, the fact that mosthigh-redshift FR II radio galaxies have nonthermal pressures similar totheir low-redshift counterparts indicates that the gaseous environmentsaround them are similar, in which case most high- redshift clusters withFR II sources should be underluminous X-ray emitters, as are theirlow-redshift counterparts. 7. Thus, the evolution in the clusteringstrength around FR II sources toward high-redshift is likely to beclosely linked to an evolution of the state of the intracluster medium.Namely, there are more clusters of low gas pressure at high redshift,and thus more FR II sources can appear in these clusters. This isconsistent with the negative evolution of the cluster X-ray luminosityfunction with redshift, and the fact that many high-redshift clustershave much lower X-ray luminosities than optically similar low-redshiftclusters.
|Brightest cluster galaxies as standard candles|
We investigate the use of brightest cluster galaxies (BCGs) as standardcandles for measuring galaxy peculiar velocities on large scales. Wehave obtained precise large-format CCD surface photometry and redshiftsfor an all-sky, volume-limited (z less than or = 0.05) sample of 199BCG. We reinvestigate the Hoessel (1980) relationship between the metricluminosity, Lm, within the central 10 kpc/h of the BCGs andthe logarithmic slope of the surface brightness profile, alpha. TheLm-alpha relationship reduces the cosmic scatter inLm from 0.327 mag to 0.244 mag, yielding a typical distanceaccuracy of 17% per BCG. Residuals about the Lm-alpharelationship are independent of BCG luminosity, BCG B - Rccolor, BCG location within the host cluster, and richness of the hostcluster. The metric luminosity is independent of cluster richness evenbefore correcting for its dependence on alpha, which provides furtherevidence for the unique nature of the BCG luminosity function. Indeed,the BCG luminosity function, both before and after application of thealpha-correction, is consistent with a single Gaussian distribution.Half the BCGs in the sample show some evidence of small color gradientsas a function of radius within their central 50 kpc/h regions but withalmost equal numbers becoming redder as becoming bluer. However, withthe central 10 kpc/h the colors are remarkably constant -- the mean B -Rc color is 1.51 with a dispersion of only 0.06 mag. Thenarrow photometric and color distributions of the BCGs, the lack of'second-parameter' effects, as well as the unique rich clusterenvironment of BCGs, argue that BCGs are the most homogeneous distanceindicators presently available for large-scale structure research.
|Observations of radio sources in clusters of galaxies with RATAN-600|
The paper reports measurements of the flux densities of radio sources in30 Abell clusters of galaxies performed with the RATAN-600 radiotelescope at 5 frequencies in the 960-7700 MHz range. The measurementswere carried out chiefly in 1984, at the northern sector of thetelescope. The flux densities measured with RATAN-600 are in goodagreement with other measurements and significantly supplement them,especially at the shortest wavelengths.
|A 20 centimeter VLA survey of Abell clusters of galaxies. III - Images and optical identifications|
Radio contour maps, models, and optical identifications for 250 radiogalaxies in Abell clusters of galaxies are presented. Consideration isgiven to the effect of environment on radio galaxies, the evolution ofradio galaxies in rich clusters, and the importance of beaming in acomplete sample of radio galaxies.
|Properties of nearby clusters of galaxies. I - A 195, A 465, A 1185, A 1213, A 1413, A 1775, A 2319 and A 2597|
A study of the properties of nearby clusters of galaxies has beenundertaken. This paper describes the data, derived from automated scansof photographic plates. Different methods for the evaluation of clustercenter, ellipticity, and orientation are compared, and errors areestimated by Monte Carlo simulations. Results are presented of theanalysis of 1256 galaxies brighter than m3 + 3 in eight Abell clusters.It is found that different methods give consistent estimates ofellipticity and orientation, provided the radial dependence of thesequantities is taken into account. It is also found that centraldensities are consistent with isothermal fits if the center is selectedas the baricenter of the cluster. For each galaxy, rectangularcoordinates, magnitude, size, ellipticity, and orientation are given.Each cluster is provided with identification maps and contour maps ofgalaxy surface density.
|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.
|A 20 CM VLA survey of Abell clusters of galaxies. I - Distance class of not greater than 3 clusters|
Nearby Abell clusters of distance class of not greater than 3 arestudied based on 20-cm VLA observations, Westerbork Synthesis RadioTelescope results, and Einstein Observatory X-ray data. No significantcorrelation is found between the 20-cm radio power and X-ray luminosity,and no evidence is found that regular-type clusters are statisticallymore likely to be radio loud than irregular-type clusters. A weakcorrelation is noted between X-ray-cooling mass-accretion rates andradio powers for central dominant galaxies in cooling-flow clusters,suggesting that either cooling accretion directly fuels the centralengine and/or cooling flows strongly interact with the radio plasma.
|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.
|Catalogue of unambiguous (Faraday-thin, one-component, spectrum-selected) rotation measures for galaxies and quasars|
This all-sky catalogue of unambiguous rotation measure (from aFaraday-thin, one-component, spectrum selection) for 674 galaxies orquasars has been compiled, ordered, and edited from the availableliterature. All the known applications of the RM distribution towardforeground objects in the Galaxy (i.e., magnetic field in 4 nearbyspiral arms and in 4 nearby interstellar magnetic bubbles) have alsobeen catalogued.
|VLBI observations of 416 extragalactic radio sources|
Very long baseline interferometry (VLBI) observations of 416 radiosources with declinations north of -45 deg have been conducted atfrequencies of 2.3 and 8.4 GHz. At 2.3 GHz, 323 of 391 radio sourcesobserved were detected with a fringe spacing of 3 milliarcsec and adetection limit of about 0.1 Jy. At 8.4 GHz, 278 of 416 radio sourceswere detected with a fringe spacing of 1 milliarcsec and a detectionlimit of about 0.1 Jy. This survey was conducted primarily to determinethe strength of compact components at 8.4 GHz for radio sourcespreviously detected with VLBI at 2.3 GHz. Compact extragalactic radiosources with strong correlated flux densities at both frequencies areused to form a high-accuracy reference frame.
|Correlation between the radio power and the X-ray luminosity for rich clusters of galaxies|
On the basis of data from a nearly complete sample of 140 Abell clustersof galaxies with z in the range of 0.02-0.075, the correlation betweenthe clusters' radio and X-ray luminosities is studied. Only a weakindirect correlation is found between these parameters. Consideration isgiven to hypotheses pertaining to the interaction between radio galaxiesand the intergalactic gas of clusters.
|Flicker of extragalactic radio sources at two frequencies|
Dual-frequency observations of flat and steep-spectrum extragalacticradio sources made at Arecibo Observatory over a 20-day period areanalyzed. As first reported by Heeschen (1982, 1984), flat-spectrumsources generally have larger intensity variations than steep-spectrumones. A structure function analysis demonstrates a qualitativedifference in the time series of the sources. The case againstinterstellar scintillation is examined, including a review of applicablescintillation theory. Relativistic source motion is treated as asolution to the brightness-temperature problems which arise if thevariations are assumed intrinsic to the sources.
|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.
|The 102.5-MHz emission of Abell clusters with Z = 0.02-0.075. I - South-latitude clusters|
A study of the low-frequency radio emission of Abell clusters isreported. The sample contains 121 clusters of galaxies with measuredredshift 0.02-0.075, declination of -10 deg to +80 deg, and locatedwithin the galactic-latitude completeness zone of the catalog. Correctedfor incompleteness, the mean cluster density is 1.5 x 10 to the -6thM/cu pc. Flux densities are estimated for all sources detected near theclusters, and estimates or upper limits are obtained for the integratedflux density of each cluster and the luminosity of its radio halo.Eleven clusters displayed detectable radio emission; in two of these andin eight other clusters, radio sources have been detected toward theoutlying regions of the cluster.
|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.
|WSRT radio observations at 1.4 GHz of 32 Abell clusters of distance class 3 and 4|
A survey of 61 Abell clusters was carried out at 1.4 GHz with theWesterbork Synthesis Radio Telescope. In this paper radio and opticaldata on 23 clusters of distance class 3 and on 9 clusters of distanceclass 4 are presented. Only the radio sources identified with galaxieslikely to be cluster members are considered here. A finding chart foreach radio galaxy and contour maps for the interesting structures areprovided.
|Radio observations of Abell clusters and a comparison with certain Einstein observations|
Areas around 70 clusters have been observed at the Arecibo Observatoryprimarily for coordination with about 60 Einstein X-ray sources. Arecibosource coordinates and flux density are tabulated, and someidentifications are made with cataloged radio sources. Statisticalestimates are made of the percentage of cluster sources among allsources in certain areas and to limits on the flux density of 430 MHz.Arecibo and other radio data are compared with the available Einsteindata of seven clusters. Not every Einstein source has a radiocounterpart, and the counterparts may variously be bilobed, tailed, orsingle. A parameter which is proportional to source continuum power at430 MHz ranges over fewer orders of magnitude than the associated sourceX-ray luminosity, with no certain correlation between these parameters.NRAO Green Bank interferometer observations of A401 and A2142 arereported.
|Linear Polarization of Extragalactic Radio Sources at 3.71 and 11.1-CENTIMETERS|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1981ApJS...46..239S&db_key=AST
|The Faraday rotation measures of extragalactic radio sources|
The rotation measures of 555 extragalactic radio sources are calculatedas a result of a large number of new linear polarization measurementscarried out at several wavelengths. A summary of references for previouspolarization measurements is included, and the procedure for optimizingthe number of unambiguous rotation measures is described.
|Extended radio sources and elliptical galaxies. V - Optical positions for 40 identified sources|
Optical positions generally accurate to about 0.4 arcsec are given forthe centers of 40 radio galaxies; the positions have been obtained bythe method described in Goodson et al., 1979. Small-diameter radio coresin extended radio structures coincide with 18 of these galaxy centers,so the identifications of the extended structures with these galaxiesare essentially unambiguous. The distribution of angular offsets of theradio cores from the centroids of the extended structures are examinedfor all such unambiguous identifications. The distribution confirms theresult of Bridle and Fomalont (1978) that more than 90% of theidentifications of clearly bifurcated radio structures are within 0.15(LAS) of their radio centroids. The reliability of the opticalidentification is examined for the 22 extended sources in this groupwhich do not have detectable radio cores.
|The structure and properties of 4C radio sources in Abell clusters -II. The declination ranges 10-20 and 50 degrees|
|Optical identifications of radio sources in the NRAO 5-GHz survey - The 'S2' and 'intermediate' surveys|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978AJ.....83..209S&db_key=AST
|Interferometer observations of radio sources in clusters of galaxies. IV|
Interferometer observations are reported for radio sources in thedirections of Abell clusters of galaxies. The results are presented inthe form of contour maps and models of the visibility data at 2695 and8085 MHz. Unlike 3CR radio galaxies and quasars, very few of thesesources show the classical double structure. Two-thirds of the clustersources display distortions and misalignments. In clusters with a radiosource and a single dominant galaxy, the two are associated and displayspecific radio morphologies. Sources with intermediate angles betweentheir twin tails point away from their respective cluster centers. Theimplications of these and other patterns for the characteristics of theintracluster medium and the dynamics of cluster radio sources arebriefly discussed.
|Spectra of sources in the NRAO 5000-MHz surveys.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974AJ.....79.1220C&db_key=AST
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