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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.
| A Redshift Survey of Nearby Galaxy Groups: The Shape of the Mass Density Profile
We constrain the mass profile and orbital structure of nearby groups andclusters of galaxies. Our method yields the joint probabilitydistribution of the density slope n, the velocity anisotropy β, andthe turnover radius r0 for these systems. The measurementtechnique does not use results from N-body simulations as priors. Weincorporate 2419 new redshifts (included here) in the fields of 41systems of galaxies with z<0.04. The new groups have median velocitydispersion σ=360 km s-1. We also use 979 archivedredshifts in the fields of eight nearly relaxed clusters with z<0.1.Within R<~2r200, the data are consistent with a singlepower-law matter density distribution with slope n=1.8-2.2 for systemswith σ<470 km s-1 and n=1.6-2.0 for those withσ>470 (95% confidence). We show that a simple, scale-freephase-space distribution function (DF)f(E,L2)~(-E)α-1/2L-2β isconsistent with the data as long as the matter density has a cusp. Usingthis DF, matter density profiles with constant-density cores (n=0) areruled out with better than 99.7% confidence.
| K-Band Properties of Well-Sampled Groups of Galaxies
We use a sample of 55 groups and six clusters of galaxies ranging inmass from 7×1011 to 1.5×1015Msolar to examine the correlation of the Ks-bandluminosity with mass discovered by Lin and coauthors in 2003. We use theTwo-Micron All-Sky Survey catalog and published redshifts to constructcomplete magnitude-limited redshift surveys of the groups. From thesesurveys we explore the IR photometric properties of groups members,including their IR color distribution and luminosity function. Althoughwe find no significant difference between the group Ksluminosity function and the general field, there is a difference betweenthe color distribution of luminous group members and their counterparts(generally background) in the field. There is a significant populationof luminous galaxies with H-Ks>~0.35, which are rarely, ifever, members of the groups in our sample. The most luminous galaxiesthat populate the groups have a very narrow range of IR color. Over theentire mass range covered by our sample, the Ks luminosityincreases with mass asLKs~M0.64+/-0.06, implying that themass-to-light ratio in the Ks band increases with mass. Theagreement between this result and earlier investigations of essentiallynonoverlapping sets of systems shows that this window in galaxyformation and evolution is insensitive to the selection of the systemsand to the details of the mass and luminosity computations.
| Unifying B2 radio galaxies with BL Lacertae objects
In an earlier paper we presented nuclear X-ray flux densities, measuredwith ROSAT, for the B2 bright sample of nearby low-luminosity radiogalaxies. In this paper we construct a nuclear X-ray luminosity functionfor the B2 radio galaxies, and discuss the consequences of our resultsfor models in which such radio galaxies are the parent population of BLLacertae (BL Lac) objects. Based on our observations of the B2 sample,we use Monte Carlo techniques to simulate samples of beamed radiogalaxies, and use the selection criteria of existing samples of BL Lacobjects to compare our simulated results to what is observed. We findthat previous analytical results are not applicable since the BL Lacsamples are selected on beamed flux density. A simple model in which BLLacs are the moderately beamed (γ~ 3) counterparts of radiogalaxies, with some random dispersion (~0.4 decades) in the intrinsicradio-X-ray relationship, can reproduce many of the features of theradio-selected and X-ray-selected BL Lac samples, including their radioand X-ray luminosity functions and the distributions of theirradio-to-X-ray spectral indices. In contrast, models in which the X-rayand radio emission have systematically different beaming parameterscannot reproduce important features of the radio-galaxy and BL Lacpopulations, and recently proposed models in which the radio-to-X-rayspectral index is a function of source luminosity cannot in themselvesaccount for the differences in the slopes of the radio- andX-ray-selected BL Lac luminosity functions. The redshift distributionand number counts of the X-ray-selected Einstein Medium SensitivitySurvey (EMSS) sample are well reproduced by our best models, supportinga picture in which these objects are beamed Fanaroff-Riley type I radiogalaxies with intrinsic luminosities similar to those of the B2 sample.However, we cannot match the redshift distribution of the radio-selected1-Jy sample, and it is likely that a population of Fanaroff-Riley typeII radio galaxies is responsible for the high-redshift objects in thissample, in agreement with previously reported results on the sample'sradio and optical emission-line properties.
| 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.
| 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.
| The LX-σ Relation for Galaxies and Clusters of Galaxies
We demonstrate that individual elliptical galaxies and clusters ofgalaxies form a continuous X-ray luminosity-velocity dispersion(LX-σ) relation. Our samples of 280 clusters and 57galaxies have LX~σ4.4 andLX~σ10, respectively. This unifiedLX-σ relation spans 8 orders of magnitude inLX and is fully consistent with the observed and theoreticalluminosity-temperature scaling laws. Our results support the notion thatgalaxies and clusters of galaxies are the luminous tracers of similardark matter halos.
| New Evidence for the Unified Scheme of BL Lacertae Objects and FR I Radio Galaxies
In this paper, we collect radio and X-ray observations for mostFanaroff-Riley I (FR I) radio galaxies in the Zirbel-Baum radio galaxysample and investigate the distribution of the radio-to-X-ray effectivespectral index, αrx, to test the unified scheme of BLLac objects and FR I radio galaxies. It is found that the range ofαrx for FR I radio galaxies is almost the same as thatfor BL Lac objects, that the distribution of αrxprobably peaks at the same position as BL Lac objects, and that thedistribution of αrx for FR I galaxies is similar tothat for BL Lac objects. These suggest that there exist two subclassesof FR I radio galaxies: one is HBL-like, and the other is LBL-like,corresponding to high-energy-peaked (HBL) and low-energy-peaked (LBL) BLLac objects, respectively. This result is consistent with previous VLAobservations and supports the unified scheme of BL Lac objects and FR Iradio galaxies.
| RBSC-NVSS Sample. I. Radio and Optical Identifications of a Complete Sample of 1556 Bright X-Ray Sources
We cross-identified the ROSAT Bright Source Catalog (RBSC) and the NRAOVLA Sky Survey (NVSS) to construct the RBSC-NVSS sample of the brightestX-ray sources (>=0.1 counts s-1~10-12 ergscm-2 s-1 in the 0.1-2.4 keV band) that are alsoradio sources (S>=2.5 mJy at 1.4 GHz) in the 7.8 sr of extragalacticsky with |b|>15deg and δ>-40deg. Thesky density of NVSS sources is low enough that they can be reliablyidentified with RBSC sources having rms positional uncertainties>=10". We used the more accurate radio positions to make reliableX-ray/radio/optical identifications down to the POSS plate limits. Weobtained optical spectra for many of the bright identifications lackingpublished redshifts. The resulting X-ray/radio sample is unique in itssize (1557 objects), composition (a mixture of nearly normal galaxies,Seyfert galaxies, quasars, and clusters), and low average redshift[~0.1].
| The Northern ROSAT All-Sky (NORAS) Galaxy Cluster Survey. I. X-Ray Properties of Clusters Detected as Extended X-Ray Sources
In the construction of an X-ray-selected sample of galaxy clusters forcosmological studies, we have assembled a sample of 495 X-ray sourcesfound to show extended X-ray emission in the first processing of theROSAT All-Sky Survey. The sample covers the celestial region withdeclination δ>=0deg and Galactic latitude|bII|>=20deg and comprises sources with a countrate >=0.06 counts s-1 and a source extent likelihood ofL>=7. In an optical follow-up identification program we find 378(76%) of these sources to be clusters of galaxies. It was necessary toreanalyze the sources in this sample with a new X-ray sourcecharacterization technique to provide more precise values for the X-rayflux and source extent than obtained from the standard processing. Thisnew method, termed growth curve analysis (GCA), has the advantage overprevious methods in its ability to be robust, to be easy to model and tointegrate into simulations, to provide diagnostic plots for visualinspection, and to make extensive use of the X-ray data. The sourceparameters obtained assist the source identification and provide moreprecise X-ray fluxes. This reanalysis is based on data from the morerecent second processing of the ROSAT Survey. We present a catalog ofthe cluster sources with the X-ray properties obtained as well as a listof the previously flagged extended sources that are found to have anoncluster counterpart. We discuss the process of source identificationfrom the combination of optical and X-ray data. To investigate theoverall completeness of the cluster sample as a function of the X-rayflux limit, we extend the search for X-ray cluster sources to the dataof the second processing of the ROSAT Survey for the northern sky regionbetween 9h and 14h in right ascension. We includethe search for X-ray emission of known clusters as well as a newinvestigation of extended X-ray sources. In the course of this search wefind X-ray emission from 85 additional Abell clusters and 56 veryprobable cluster candidates among the newly found extended sources. Acomparison of the X-ray cluster number counts of the NORAS sample withthe ROSAT-ESO Flux-limited X-Ray (REFLEX) Cluster Survey results leadsto an estimate of the completeness of the NORAS sample of ROSAT All-SkySurvey (RASS) I extended clusters of about 50% at an X-ray flux ofFX(0.1-2.4 keV)=3×10-12 ergs s-1cm-2. The estimated completeness achieved by adding thesupplementary sample in the study area amounts to about 82% incomparison to REFLEX. The low completeness introduces an uncertainty inthe use of the sample for cosmological statistical studies that will becured with the completion of the continuing Northern ROSAT All-Sky(NORAS) Cluster Survey project. Results reported here are based onobservations made with the Multiple Mirror Telescope, a joint facilityof the Smithsonian Institution and the University of Arizona.
| The RASSCALS: An X-Ray and Optical Study of 260 Galaxy Groups
We describe the ROSAT All-Sky Survey-Center for Astrophysics LooseSystems (RASSCALS), the largest X-ray and optical survey of low-massgalaxy groups to date. We draw 260 groups from the combined Center forAstrophysics and Southern Sky Redshift Surveys, covering one-quarter ofthe sky to a limiting Zwicky magnitude of mz=15.5. We detect61 groups (23%) as extended X-ray sources. The statistical completenessof the sample allows us to make the first measurement of the X-rayselection function of groups, along with a clean determination of theirfundamental scaling laws. We find robust evidence of similarity breakingin the relationship between the X-ray luminosity and velocitydispersion. Groups with σp<340 km s-1 areoverluminous by several orders of magnitude compared to the familiarLX~σ4 law for higher velocity dispersionsystems. An understanding of this break depends on the detailedstructure of groups with small velocity dispersionsσp<150 km s-1. After accounting forselection effects, we conclude that only 40% of the optical groups areextended X-ray sources. The remaining 60% are either accidentalsuperpositions or systems devoid of X-ray emitting gas. Combining ourresults with group statistics from N-body simulations, we find that thefraction of real, bound systems in our objectively selected opticalcatalog is between 40%-80%. The X-ray detections have a medianmembership of nine galaxies, a median recession velocity cz=7250 kms-1, a median projected velocity dispersionσp=400 km s-1, and a median X-ray luminosityLX=3×1042 h-2100 ergss-1, where the Hubble constant is H0=100h100 km s-1 Mpc-1. We include a catalogof these properties, or the appropriate upper limits, for all 260groups.
| The Asiago-ESO/RASS QSO Survey. I. The Catalog and the Local QSO Luminosity Function
This paper presents the first results of a survey for bright quasars(V<14.5 and R<15.4) covering the northern hemisphere at Galacticlatitudes |b|>30°. The photometric database is derived from theGuide Star and USNO catalogs. Quasars are identified on the basis oftheir X-ray emission measured in the ROSAT All-Sky Survey. The surfacedensity of quasars brighter than 15.5 mag turns out to be(10+/-2)×10-3 deg-2, about 3 times higherthan that estimated by the PG survey. The quasar optical luminosityfunction (LF) at 0.04
| Surface photometry of radio loud elliptical galaxies from the B2 sample
V-band CCD imaging is presented for 72 galaxies from the B2 radio sample(Colla et al. \cite{colla}; Fanti et al. \cite{fanti78}), with redshiftsup to 0.2 and radio powersP408=1023-1026.5 W Hz-1.According to the morphology on the optical images 57 galaxies areclassified as ellipticals, 6 as spirals and 7 as irregular. Surfacephotometry of the sample of ellipticals was obtained fitting ellipses tothe light distribution. The light profile of these galaxies generallyfollows a de Vaucouleurs law, although in three cases the profiles showlarge excesses relative to the r1/4 law at large radii. Thefitted mu_e and r_e parameters for the de Vaucouleurs galaxies are givenin the paper. Three of the ellipticals show a bright nucleus. One ofthem is a known broad line radio galaxy (B2 1833+32) and the remainingtwo are Markarian galaxies, classified in the literature as BL Lacobjects (B2 1101+38 and B2 1652+39). The radial profiles forellipticity, position angle, and B_4 term of the Fourier analysis arepresented in the paper, and the morphological peculiarities of theellipticals are described, including the presence of shells, tails,nuclear dust, isophote twisting, off-centering, and boxiness or disknessof the isophotes. Only one of the galaxies in this work is included inthe subsample of B2 radio galaxies with well-defined jets (Parma et al.\cite{parma87}). In this sense the present sample complements the sampleof 24 radio galaxies with well-defined radio jets in Parma et al. forwhich a similar study was presented in González-Serrano et al.(\cite{gserrano93}). The irregular galaxy B2 0916+33 appears to bemisclassified, and we suggest that the right identification of the radiosource is a nearby point like object with V=18.45 mag. The spiral galaxyassociated with B2 1441+26 is also misclassified. A point-like opticalobject with V=18.88 mag, located at ~ 36 arcsec from the originalidentification and coincident with the radio core is the most probablecounterpart. Table 4 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html Complete Figure 1 and Figure 2are only available at http://www.edpsciences.org
| X-ray observations of low-power radio galaxies from the B2 catalogue
We present an analysis of X-ray data, taken with ROSAT, for awell-defined sample of low-power radio galaxies from the Bologna B2catalogue. Where possible, the HRI has been used in order to takeadvantage of the high spatial resolution provided by this instrument. Avariety of models are fitted to radial profiles in order to separate theresolved and unresolved X-ray emission from the galaxies. We demonstratea strong, approximately linear, correlation between the luminosities ofthe unresolved X-ray components and the 5-GHz luminosities of the radiocores in this sample. This suggests a physical relationship between thesoft X-ray emission of radio galaxies and the jet-generated radio coreemission. We infer a nuclear jet-related origin for at least some of theX-ray emission.
| The ROSAT Brightest Cluster Sample - I. The compilation of the sample and the cluster log N-log S distribution
We present a 90 per cent flux-complete sample of the 201 X-ray-brightestclusters of galaxies in the northern hemisphere (delta>=0 deg), athigh Galactic latitudes (|b|>=20 deg), with measured redshiftsz<=0.3 and fluxes higher than 4.4x10^-12 erg cm^-2 s^-1 in the0.1-2.4 keV band. The sample, called the ROSAT Brightest Cluster Sample(BCS), is selected from ROSAT All-Sky Survey data and is the largestX-ray-selected cluster sample compiled to date. In addition to Abellclusters, which form the bulk of the sample, the BCS also contains theX-ray-brightest Zwicky clusters and other clusters selected from theirX-ray properties alone. Effort has been made to ensure the highestpossible completeness of the sample and the smallest possiblecontamination by non-cluster X-ray sources. X-ray fluxes are computedusing an algorithm tailored for the detection and characterization ofX-ray emission from galaxy clusters. These fluxes are accurate to betterthan 15 per cent (mean 1sigma error). We find the cumulative logN-logSdistribution of clusters to follow a power law kappa S^alpha withalpha=1.31^+0.06_-0.03 (errors are the 10th and 90th percentiles) downto fluxes of 2x10^-12 erg cm^-2 s^-1, i.e. considerably below the BCSflux limit. Although our best-fitting slope disagrees formally with thecanonical value of -1.5 for a Euclidean distribution, the BCS logN-logSdistribution is consistent with a non-evolving cluster population ifcosmological effects are taken into account. Our sample will allow us toexamine large-scale structure in the northern hemisphere, determine thespatial cluster-cluster correlation function, investigate correlationsbetween the X-ray and optical properties of the clusters, establish theX-ray luminosity function for galaxy clusters, and discuss theimplications of the results for cluster evolution.
| H_2O megamaser emission from FR I radio galaxies
A systematic search for 22 GHz H_2O megamaser emission is reported for50 nearby (z la 0.15) FR I galaxies. No detection was obtained, implyingthat ultraluminous H_2O masers (L_H_2O > 10(3) Lsun) mustbe rare in early-type galaxies with FR I radio morphology. Despitehigher radio core luminosities the detection rate for our sample islower than in similar surveys of late-type Seyfert galaxies. Thispuzzling difference between Seyferts and low-power radio galaxies couldbe explained in several ways: a) the maser emission is saturated andtherefore independent of the radio core luminosity, b) the masers areunsaturated and originate in a thin circumnuclear gas disk, so the`seed' radio continuum would come from the far jet which isrelativistically dimmed or c) the amount, kinematics, or thedistribution of the molecular gas in the nuclei of Seyferts and radiogalaxies is different. Further studies of maser properties may provideclues to the differences between radio-loud and radio-quiet AGN.
| Polarization of low-luminosity radio galaxies: The 6 CM data
Polarization data are presented for 62 B2 radio galaxies. The sourceswere observed at 6 cm in different configurations of the VLA. Theresults are given as integrated and mean component parameters. We alsopresent maps of total intensity with superimposed vectors representingthe fractional polarization and position angle. We compare these newdata with older data at 20 cm and discuss briefly depolarization,rotation of polarization angle and geometry of the magnetic field.
| Asymmetric depolarization in double low-luminosity radio galaxies.
To investigate the presence of the Laing-Garrington effect (i.e. thelobe containing the jet more depolarized than that containing thecounter-jet), we analyse polarization data at 6 and 20cm for a sample ofdouble low-luminosity radio galaxies. The effect is well visible,although not very strong. We therefore confirm what was inferred in aprevious paper based on data at one frequency (20cm) only. Furthermore,we find that radio galaxies with strong radio cores show a morepronounced asymmetry in depolarization. We conclude that the presence ofthe Laing-Garrington effect in our sample is a indication thatrelativistic motions do occur on the kpc scale of low-luminosity radiogalaxies as recently suggested by theoretical arguments andobservational evidence.
| 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.
| The CfA Redshift Survey: Data for the NGP +36 Zone
We have assembled redshifts for a complete sample of 719 galaxies withm_zw_ <= 15.5 in the declination range 32.5^deg^ <= δ <=38.5^deg^ and right ascension range 8^h^ <= α <= 17^h^. Wehave determined morphological types for all galaxies in the magnitudelimited sample by direct inspection of the POSS-O plates. 576 of theredshifts are measurements from Mount Hopkins, and 405 are newredshifts. We also include new redshifts for 77 fainter galaxies in thesame strip.
| Corrections and additions to the third reference catalogue of bright galaxies
List of corrections and additions to the Third Reference Catalogue ofBright Galaxies (RC3) are given. The corrected version of the catalogue(RC3.9b), dated April 1994, is currently available through the nationaldata centers.
| Polarization in low luminosity radio galaxies
Polarization data are presented for 69 B2 radiogalaxies. The sourceswere observed at 20 cm in different configurations of the VLA. Theresults are given as integrated and mean component parameter and arecompared with those from similar studies. We also present maps of totalintensity with superimposed vectors representing the fractionalpolarization and position angle for the most interesting sources.Information on individual sources are given when interesting structuresare present.
| Optical line-emitting gas and radio emission - Evidence for correlation in low-luminosity radio galaxies
Narrow-band H-alpha + (N II) images of a sample of low-luminosity B2radio sources are used to investigate the correlations between radio andoptical emission-line properties. It is shown that the correlationbetween radio and emission-line luminosity - previously established forhigh-power radio galaxies - extends over five decades in radioluminosity and includes the low-radio power sources. The compact radiosources have emission-line excesses relative to the other sources in thesample of the same radio power, as well as far-IR emissioncharacteristics of emission from cool dust. Although continuityarguments can be used to show that the ionized gas in most of thelow-luminosity sources is likely to be photoionized by the ActiveGalactic Nucleus, it is possible that additional ionizing sourcescontribute in the compact, emission-line excess objects. A program ofdetailed spectroscopic observations is required to investigate theunderlying physical mechanisms.
| Very large array observations of radio-selected dumbbell galaxies
An unbiased sample of radio sources associated with optical dumbbellgalaxies is presented. This sample has been assembled to study therelationship between the radio and optical properties of radio-louddumbbell galaxies. High-quality radio data already exist for a number ofthe sources in the sample, but those sources without good data have beenobserved with the very large array at 20 or 6 cm. These new observationsare described and radio images are presented. Analysis of both the radiostructure of the sources and their radio luminosity has been carriedout, and a comparison is made with the properties of a complete sampleof radio sources associated with single galaxies. Radio sourcesassociated with dumbbell galaxies are found on average to have moredistorted structures than sources associated with single galaxies,demonstrating the influence of the dumbbell dynamics in shaping thelarge-scale structure of the radio sources. It is shown that in therange 10 exp 24 - 10 exp 26 W/Hz at 408 MHz the radio luminosityfunction of dumbbell systems is flatter than that of single-galaxy radiosources, indicating that a close companion may trigger a radio source inthe main galaxy, or alternatively increase the luminosity of an existingradio source.
| 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.
| Observations of faint radio galaxies with the Ratan-600 radio telescope
The results of observations of 79 faint radio galaxies from the BolognaSurvey with the RATAN-600 radio telescope at the frequency 3.95 GHz arepresented. The dependences of spectral indices of radio emission on theratio of radio and optical luminosities are analyzed. The dependence oflinear sizes of radio galaxies on these ratios and on spectral indiceswas studied. It is shown that median angular sizes and spectral indicesincrease with flux density. It is also shown that among radio galaxieswith flat spectra objects of small linear sizes (less than 10 kpc) occurmuch more frequently than among radio galaxies with steep spectra.
| Infrared studies of elliptical galaxies. II - A radio-selected sample
An IR survey of radio galaxies in the Bologna B2 catalog is reported. Itis found that 40 percent of the sample has IR luminosities of at leastone billion solar luminosities, as opposed to about 8 pecent of normalellipticals. The galaxies are inhomogeneous in their IR properties. Themost IR-luminous galaxies are those listed as peculiar by Zwicky.Statistically, these galaxies are strikingly different from Seyfertgalaxies in their IR properties in that they show much more radioemission in comparison with their IR emission than do Seyferts, evenwhen the emission from the extended radio lobes has been discounted.
| Groups of galaxies in the Center for Astrophysics redshift survey
By applying the Huchra and Geller (1982) objective group identificationalgorithm to the Center for Astrophysics' redshift survey, a catalog of128 groups with three or more members is extracted, and 92 of these areused as a statistical sample. A comparison of the distribution of groupcenters with the distribution of all galaxies in the survey indicatesqualitatively that groups trace the large-scale structure of the region.The physical properties of groups may be related to the details oflarge-scale structure, and it is concluded that differences among groupcatalogs may be due to the properties of large-scale structures andtheir location relative to the survey limits.
| Study of a field in the Coma supercluster. I - Automated galaxies count
A IIIaJ Palomar Schmidt plate of the eastern end of a filament ofgalaxies found by Fontanelli (1984) in the Coma cluster region has beenexamined. The galaxy selection was performed using a classical Bayesianclassification based on the diagram of integrated density versus thearea, allowing all the nonstellar objects to be identified. Coordinates,amplitudes, areas in pixels, and morphological types are given for 7582galaxies. A real-time reduction technique for image segmentation is usedto identify galaxy condensations, and estimations of the parameters,position, axis, and orientation of these condensations are presented.
| Relative velocities of dumbbell galaxies
A systematic study of a morphologically-selected sample of dumbbellgalaxies is presented. A dumbbell/multiple nuclei subclassificationscheme is introduced. The single-object velocity dispersion of dumbbellcomponents in Abell-type clusters is 436 + or - 88 km/sec, which issignificantly smaller than that of normal cluster galaxies and ofmultiple nuclei systems. A detailed analysis of this sample, taking intoaccount various projection effects, indicates that the two components ofdumbbell pairs are physically associated, and probably in circularorbits around a common center. A relative rotation velocity of 1200km/sec at a separation of 40 kpc is indicated. This translates into asingle-object velocity of 600 km, intermediate between the typicalrotation velocity in the central part of a cD galaxy and that in thecluster-at-large. Furthermore, the rotation curve appears to be risingin this radial range. The data provide direct evidence of the existenceof a dark intracluster medium on a scale of 20-50 kpc.
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