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K-band Properties of Galaxy Clusters and Groups: Brightest Cluster Galaxies and Intracluster Light
We investigate the near-infrared K-band properties of the brightestcluster galaxies (BCGs) in a sample of 93 X-ray galaxy clusters andgroups, using data from the Two Micron All Sky Survey. Our clustersample spans a factor of 70 in mass, making it sensitive to any clustermass-related trends. We derive the cumulative radial distribution forthe BCGs in the ensemble and find that 70% of the BCGs are centered inthe cluster to within 5% of the virial radius r200; thisquantifies earlier findings that BCG position coincides with the clustercenter as defined by the X-ray emission peak. We study the correlationsbetween the luminosity of the BCGs (Lb) and the mass and theluminosity of the host clusters, finding that BCGs in more massiveclusters are more luminous than their counterparts in less massivesystems and that the BCGs become less important in the overall clusterlight (L200) as cluster mass increases. By examining a largesample of optically selected groups, we find that these correlationshold for galactic systems less massive than our clusters(<3×1013 Msolar). From the differencesbetween luminosity functions in high- and low-mass clusters, we arguethat BCGs grow in luminosity mainly by merging with other luminousgalaxies as the host clusters grow hierarchically; the decreasing BCGluminosity fraction (Lb/L200) with cluster massindicates that the rate of luminosity growth in BCGs is slow compared tothe rate at which clusters acquire galaxy light from the field or othermerging clusters. Utilizing the observed correlation between the clusterluminosity and mass and a merger tree model for cluster formation, weestimate that the amount of intracluster light (ICL) increases withcluster mass; our calculations suggest that in 1015Msolar clusters more than 50% of total stellar mass is inICL, making the role of ICL very important in the evolution andthermodynamic history of clusters. The cluster baryon fractionaccounting for the ICL is in good agreement with the value derived fromcosmic microwave background observations. The inclusion of ICL reducesthe discrepancy between the observed cluster cold baryon fraction andthat found in hydrodynamical simulations. Based on the observed ironabundance in the intracluster medium, we find that the ICL predicted byour model, together with the observed galaxy light, match the ironmass-to-light ratio expected from simple stellar population models,provided that the Salpeter initial mass function is adopted. The ICLalso makes it easier to produce the ``iron excess'' found in the centralregions of cool-core clusters.
| The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| The death of FR II radio sources and their connection with radio relics
Radio relic sources in galaxy clusters are often described as theremnants of powerful radio galaxies. Here we develop a model for theevolution of such relics after the jets cease to supply energy to thelobes. This includes the treatment of a relic overpressured with respectto its gaseous surroundings even after the jets switch off. We alsodetermine the radio emission of relics for a large variety ofassumptions. We take into account the evolution of the strength of themagnetic field during the phase of relativistic particle injection intothe lobes. The resulting spectra show mild steepening at around 1 GHzbut avoid any exponential spectral cut-offs. The model calculations areused to fit the observed spectra of seven radio relics. The quality ofthe fits is excellent for all models discussed. Unfortunately, thisimplies that it is virtually impossible to determine any of theimportant source parameters from the observed radio emission alone.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| An extreme example of a radio relic in Abell 4038
A radio source with a spectral index of -2.2 between 0.08 and 1.425GHzhas been observed at the Very Large Array (VLA) at 1.425GHz withresolution~3 arcsec. The projected linear length of the source is 56 kpcwith an average projected distance of 42 kpc from the centroid of therich southern cluster Abell 4038, assuming the source is in the cluster.The physical parameters of the source include a high minimum-energyfield (B_me) of 38muG, which is unusual for a source of low surfacebrightness and relaxed appearance, but is explained by its unusuallysteep spectrum. Although its radio morphology has some characteristicsof a narrow-angle-tail source (NAT), the absence of an identified hostgalaxy (m_R>=23.0) makes it unlikely that the source is a workingradio galaxy. The relic is probably the remains of an FR II radio galaxythat was once energized by a particular bright cluster elliptical now 18kpc to its east. The density of the intracluster gas has been sufficientto confine the source and preserve its morphology, permitting the sourceto age and its spectrum to steepen through synchrotron and inverseCompton energy losses.
| 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 20 Centimeter VLA Survey of Abell Clusters of Galaxies. VII. Detailed Radio Images
We present detailed radio images, and models, obtained with the VeryLarge Array at 20 cm for 199 radio galaxies in Abell clusters ofgalaxies.
| A VLA survey of rich clusters of galaxies. III. The weaker sources: maps and identifications.
We present radio and optical parameters for 737 weak sources in 60 Abellcluster fields observed with the Very Large Array (VLA) using scaledarrays at 1.5 and 4.9 GHz. The measurements extend to a lower 1.5 GHzlimit of 1.0 mJy and comprise a complete sample with 1.5-GHz fluxdensity 2.5 < S_1.5 < 20 mJy. The combined sky area within thehalf-power circle on the maps is 3.5 x 10^-3 sr, and the cluster fieldsare distributed over 24 h of right ascension and between declinations+35deg and -30deg. Contour maps of the extended sources at 1.5 GHz arepresented and source parameters such as position, angular size andspectral index are tabulated. We also derive the emitted power andlinear size for those sources with published redshifts. We try toidentify the radio sources with optical images on the Palomar and SERCsurvey plates and give their accurate optical positions, morphologiesand apparent magnitudes.
| A Dynamical Analysis of the Poor Galaxy Clusters Abell 2626 and Abell 2440
We use 189 new radial velocities and R band CCD photometry to study thegalaxy clusters Abell 2626 and Abell 2440. By combining these newoptical constraints with archival x-ray images and gas temperaturemeasurements, we investigate the dynamical nature of both systems. Wederive masses, luminosity functions, and mass-to-light ratios. Thesymmetric x-ray emission from A2626 suggests a relaxed, single-componentsystem; however, our sample of 159 redshifts reveals a complex,three-component cluster at cz ~ 17500 km/s. One of these components is atypical x-ray bright cluster, a second has a cluster-like galaxypopulation with a much lower central galaxy and gas density, and thethird is a background structure with field galaxy composition. Acomparison of the magnitude distributions within the two subclusterssuggests that A2626 is a merger in progress (at 93% confidence). Virialmasses and a composite luminosity function for a region with projectedradius r= 1.5h^-1^ Mpc yield a mass- to-light ratio M/L_R_ ~ 610h.Analysis of the x-ray emission from the primary component yields a gasmass function of ~2.2h^-3/2^% and a baryon fraction of ~3.4%. A radialinfall model indicates that the virial mass may be an underestimate. Thebimodal x-ray emission and elongated galaxy distribution of A2440 havebeen studied before (Baier 1979; Beers et al. 1991). With deeper, CCD Rband photometry we demonstrate a striking correspondence between thegalaxy and cluster gas distributions. The galaxy distribution has threemain components, each associated with a giant elliptical galaxy. The twolarger peaks in the galaxy distribution coincide with the primary peaksin the x-ray emission, and the third is associated with a significantx-ray surface brightness enhancement. We use this galaxy-gascorrespondence, 48 redshifts, and the structure of the x-ray emission toargue that the subclusters are bound within a single system, and thatthe two primary components are beginning to merge. The compositeluminosity function and estimates of the subcluster virial massesindicate a mass-to-light ratio in the range M/L_R_ = 660h to 880h.
| Optical Spectroscopy of Radio Galaxies in Abell Clusters II. BL Lacs and FR I Unification
As part of our optical spectroscopic study of radio galaxies in Abellclusters, we report a search for BL Lac phenomena in our sample. As anindicator of possible nonthermal activity in the nuclei of our radiogalaxies, we report D(4000), a measure of the 4000 A break, for 190objects. None of the objects in our sample are found which meet thetions for BL Lac objects both for D(4000) and for weakness of emissionlines. We do find 15 objects which have diluted 4000 A breaks[D(4000)<= 1.8], and these are discussed individually. At least fourof them appear to have weak nonthermal activity which may be related tothe BL Lac phenomena. These results appear to be in conflict with thesimplest BL Lac/FR I unification model. Several ways out of this dilemmaare discussed. Perhaps the most likely change in this model is theinclusion of FR II radio galaxies as part of the parent population of BLLac objects.
| 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.
| Radio sources observed with the Culgoora circular array
Presented is a final updated and recalibrated list of sources that wereobserved with the Culgoora circular array in the interval 1970-1984. Thepresent list contains all the sources that were contained in theCulgoora-1, 2, 3 Lists plus additional sources resulting from a surveyof 353 Abell clusters of galaxies. The electronic version of theCulgoora List, with appropriate documentation, is available from theEinstein On-Line Service.
| A 20 CM Survey of Abell Clusters of Galaxies. V. Optical Observations and Surface Photometry
We present results from a program of optical imaging of 265 radiogalaxies in rich clusters. Using isophotal surface photometry, weinvestigate the optical properties such as the morphology, surface-brightness profiles, surface-brightness/size relationships,ellipticities, and the frequency of nonelliptical isophotes. The resultsare compared to a "normal" nonradio-selected sample of ellipticalgalaxies from the same clusters. The goal is to determine if the parentpopulation of FR I radio galaxies can be distinguished optically fromradio-quiet galaxies. The results of the analysis are that clusterellipticals are a very homogeneous class of objects. The opticalproperties are consistent with a one-parameter family, where the opticalluminosity is the fundamental parameter. In all tests considered, radio-loud FR I galaxies cannot be distinguished optically from radio-quietgalaxies selected from the same environment. The local density of nearbycompanions (<20 kpc) and the frequency of morphological peculiaritiesor tidal interactions are not statistically different between theradio-loud and quiet samples. There is some suggestion from comparisonto published samples of non-cluster radio galaxies, that the clusterenvironment is not condusive to long-lived tidal interactions, and thatsuch events may be more important to galaxy evolution in poor groups andlower density environments. Such events appear to have little influenceon the formation of FR I radio galaxies in rich clusters. The resultsare consistent with the idea that all elliptical galaxies may at sometime (or many times) contain powerful (rR I) radio sources.
| A 20 CM VLA Survey of Abell clusters of galaxies. 4: The radio sample and cluster properties
This is the fourth in a series of papers describing an in depth study ofa large statistical sample of radio galaxies in Abell clusters. Thissample forms the basis of a detailed optical and radio study of the hostgalaxy properties, environments, and evolutionary models for radiogalaxies as a class of objects. In this paper, we examine the radiodetection statistics as a function of cluster morphological type, galaxyrichness, and spatial location within the cluster distribution. Theserelationships are also parameterized as a funtion of radio power. Thespatial distributions of the radio sources as a function of distancefrom the cluster center indicate that radio galaxies are preferentiallylocated at small radii from the center of the cluster potential. This isobserved as a factor of 2-3 excess over that predicted by a King-modelsurface-density distribution. The excess is higher in the upper radiopower bin. This result is easily explained, however, from the spatialdistribution of the brightest galaxies and the relationship betweenradio and optical luminosity. The sample is divided into richnessclasses 0, 1, and 2, according to Abell's criterion. and in two radiopower ranges. While simple counting shows that richer clusters have moreradio galaxies in both radio power bins, when the detections are scaledto the number of galaxies surveyed in each cluster, no significantcorrelations are found. This result implies that the number of radiogalaxies detected simply scales with the number of galaxies surveyed.The higher galaxy density (and presumably higher ICM gas density) inricher clusters does not appear to affect the rate of radio sourceformation. The clusters are divided into Rood-Sastry and Bautz-Morganmorphological types. While it would appear that the more regularclusters have higher radio detection rates, when the classes arenormalized to the number of galaxies, the radio detection rates arefound to be identical regardless of cluster morphology. In conclusion,it is the optical properties of the host galaxy which most influenceboth the radio detection rate and the radio source properties. Thecluster properties, galaxy density, and spatial location of the galaxydo not significantly affect the observed radio statistics.
| Optical spectroscopy of radio galaxies in Abell clusters. 1: Redshifts and emission-line properties
We present results of a program of optical spectroscopy of radiogalaxies in rich clusters. Redshifts are reported for 268 radio galaxiesor close companions in Abell clusters and 36 objects which turned out tobe foreground or background objects. Absolute line strengths are alsoreported for the 3727 A (O II) line and the (N II)/H alpha complex. Wefind no evidence that the radio activity in our sample of mostly FR Iradio galaxies is associated with emission-line luminosities above thosefound in normal galaxies of the same absolute magnitude and opticaltype. We also find that the radial velocity differences between radiogalaxies and the cluster mean seem mainly to be a function of galaxyabsolute magnitude rather than radio properties.
| Samples of ultra-steep spectrum radio sources.
Radio sources with ultra-steep spectra (USS) have been found to beexcellent tracers of galaxies at redshifts z>~2. In order to obtain alarge sample of z>~2 galaxies, we have defined several newflux-limited samples of USS radio sources. These samples are selected ata range of frequencies from 38MHz to 408MHz and are fainter by a factorof three than the previously well-studied 4C samples of USS sources. Wefind that complete samples of radio sources with angular diameters<~1arcmin selected at 38MHz contain relatively fewer USS sources thansamples of small radio sources selected at higher (>~150MHz)frequencies. This is interpreted as due to flattening of the spectra ofdistant USS sources at frequencies <100MHz. As a preliminary tooptical imaging and spectroscopy, snapshot observations of sources fromthese samples have been made with the VLA at 1.5arcsec resolution. Wepresent the positions, flux densities and radio structures for a totalnumber of 605 sources derived from these observations. Our VLA imagesindicate that samples of USS sources selected at 38MHz contain a smallerproportion of small sources and a larger proportion of diffuse sourcesthan USS sources selected at higher (>~150MHz) frequencies. This isconsistent with the samples of 38MHz - selected USS sources containing alarger fraction of relatively nearby radio sources, perhaps in clustersof galaxies.
| Relic radio galaxies: evolution of synchrotron spectrum
The very steep spectrum radio sources (VSSRSs) found in clusters ofgalaxies are believed to be relic radio galaxies whose nuclei haveceased their activity. The unusually steep spectra of the sources(α<=-2.0) are explained by the synchrotron losses of energy ofrelativistic electrons after the cessation of the injection of freshparticles into the radio lobes. Such strongly evolved spectra provide agood opportunity to choose between the two principal models of spectralageing - that of Kardashev and Pacholczyk (which assumes an anisotropicpitch angle distribution of the relativistic electrons) and that ofJaffe and Perola (which assumes an isotropic distribution of them).However, when the integrated spectra of the relic radio sources areconsidered, an additional factor, a finite time of the injection of therelativistic particles, could be important. We modify the two models totake this factor into account. We also study the role of the energy lossdue to inverse Compton scattering of 3K background photons and foundthat this prevents the formation of the power law region with spectralindex (4/3)α_0_-1 in the KP-model unless the magnetic fields arestronger than 10^-4^ G. The position of the high-frequency cutoff causedby the losses depends only on the time since activity ceased (and onredshift) and as a result the shape of our version of the KP-spectrumcould be used to estimate the magnetic fields strength in the VSSRSs andcorrespondingly to test the equipartition hypothesis. We compared thepredicted spectra with the observed ones of six VSSRSs - Mol0100-221,Cul0038-096, 4C63.10, 4C38.39, 3C318.1, and 3C464. The goodness of fitsof our models and estimations of their free parameters were determinedby using the minimum χ^2^ technique. Remarkably good fits areprovided by our version of the KP-model with the injection spectralindex α_0_=-0.5, and the exponential cutoff at high frequenciescaused by the inverse Compton losses. In the context of the model wefound typical magnetic fields in the VSSRSs of order 10^-5^G, severaltimes higher than the equipartition values, and the typical time oftheir decay, τ =~10^8^yr. Our version of the JP-model provides worsefits. However, significant improvement can be achieved if one takes intoaccount possible strong variations of magnetic field strength(H_max_/H_min_ > 3) in these sources. By considering the activestages of these VSSRSs we found that their progenitors were highluminosity (>=10^43^ erg/s) radio galaxies rarely found in clustersof galaxies. Most other relic sources probably escape from flux limitedsamples due to a drop of their luminosity.
| A Complete Sample of Sources in the North Ecliptic CAP Selected at 38-MHZ - Part Two - CCD Observations and Their Implications
We present 55 CCD images and six spectra of a complete sample of 57 8Cradio sources selected at 38 MHz in the North Ecliptic Cap. All buteight sources appear to be optically identified to a limiting magnitudeof R ~ 23.5. Using spectroscopic redshifts where available and redshiftestimates from the R magnitudes of the identifications otherwise,together with data on a bright comparison sample, we investigate thedependence of radio spectral index and physical size on redshift andradio luminosity. We find evidence that spectral index is more stronglycorrelated with redshift than with radio luminosity, and that there is aweak anticorrelation of size with redshift. The number density evolutionseen within and between the samples is discussed, as are the relativefractions of quasars and cluster halo sources in the two samples. Wealso comment on the use of radio spectral indices in the search fordistant radio galaxies.
| 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.
| KISO survey for ultraviolet-excess galaxies. XIV.
The 14th list and identification charts of the UV-excess galaxiesdetected on the multicolor plates taken with the Kiso Schmidt telescopefor 10 survey fields are presented. In the sky area of some 300 sq deg,about 470 objects are cataloged down to the photographic magnitude ofabout 17.5.
| Isophotal shapes of early-type galaxies. I - Elongated ellipticals
Forty-three very elongated elliptical galaxies were observed in directB, V, R CCD imaging with the 2-m telescope of Pic-du-Midi Observatoryand with the Canada-France-Hawaii telescope in fairly good seeingconditions. Five galaxies do not show an elliptical structure: threeclearly show spiral features and one is a dumbbell. The 38 othergalaxies were analyzed with an isophote-fitting procedure which allowsone to derive the deviations from pure ellipses in terms of thecoefficients of a Fourier series. The geometrical parameters of these 38elongated ellipticals are presented, with brief comments on theirpeculiarities.
| Radio-emission spectra and surface brightnesses of radio galaxies
It is shown that radio galaxies with flat radio-emission spectra have,on the average, significantly higher optical surface brightness thanradio galaxies with steep spectra. The results obtained also suggestthat radio galaxies with flat spectra are in a more active phase ofevolution than galaxies with steep spectra. Intense star-formationprocesses appear to be occurring in the galaxies with flat spectra.
| 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.
| CD galaxies of apparent supergiant sizes due to the curvature of space
Evidence for a positively curved universe is examined, and a model isdeveloped by combining two two-dimensional subspaces which are closedinto themselves due to curvature, to create a model of three-dimensionalspace of the same properties. A law of fictitious magnification isproposed. Indirect evidence for spherically curved space (and for thenonexistence of negative curvature) includes superluminal velocities,the existence of supergiant galaxies such as cD's, the superposition ofgalaxies, and the occurrence of background radiation. The theory impliesthe existence of another interpretation of spectra into redshifts. Theoccurrence of a gravitational lens effect, giving amplification of thecontours of foreground galaxy images, results in spectra beingintermixed.
| 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.
| WSRT and VLA observations of very steep spectrum radio galaxies in clusters
A sample of very steep spectrum radio sources in rich clusters ofgalaxies has been observed at 20.5 cm with the VLA and at 49 cm with theWSRT. They are typical of sources which are confined by theintergalactic medium and they represent a late stage of evolution ofradio sources in which synchrotron losses dominate and expansion lossesno longer occur. Their spectra are in agreement with theoretical modelsof evolution governed on one hand by input of energy from the nucleus ofthe galaxy and on the other hand by synchrotron losses (Kardashev,1962). One important consequence can be derived from the properties ofthese sources. The diffusion of relativistic electrons from the radiolobes in the intergalactic medium is not the primary mode of lossesduring the evolution of such confined radio sources.
| 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.
| The Trivariate / Radio Optical X-Ray / Luminosity Function CD Galaxies - Part Two - the Fuelling of Radio Sources
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983A&A...125..223V&db_key=AST
| HEAO 1 observations of quiescent X-ray emission from flare stars
The HEAO A-2 data were searched at the positions of the 70 known flarestars for evidence of X-ray emission. Thirteen of them appear to bedetected at the equal to or greater than 3 sigma level. Their X-rayluminosities in the 2-20 keV energy band are in the range 5 x 10 to the28th - 6 x 10 to the 29th ergs/s and L(x)/L(bal) approximately 0.0001 to0.01. There were no detectable X-ray flare events during the time ofHEAO 1 observations. This detection, therefore, refers to the quiescentstate X-ray emission from the coronae of these stars. It appears thatintense coronae belonging to fairly active flare stars are beingobserved. X-ray variability over periods of 6 months was observed forseveral of them.
| Radio and X-ray galaxies in Abell 566
Radio and X-ray observations are presented for Abell 566. The X-rayemission indicates a relatively cool gas (2 keV) with a fairly widedistribution (600 kpc core radius). Two enhancements in the smooth X-raydistribution are tentatively associated with 2 radio galaxies which arecluster members. One of these has a very steep radio spectrum. Thepressure in this source from relativistic particles and the magneticfield is comparable to the thermal pressure of the cluster gas. Thus,the steep radio spectrum may be explained by thermal confinement and aturnoff of particle injection about 100-million years ago. A secondX-ray source 17 arcmin from the field center, appears to be associatedwith a distant Seyfert. It is probably an example of the newly isolatedclass of Seyferts which have variable, soft X-ray emission.
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