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Stellar populations in the centres of brightest cluster galaxies
This paper is part of a series devoted to the study of the stellarpopulations in brightest cluster galaxies (BCGs), aimed at settingconstraints on the formation and evolution of these objects. We haveobtained high signal-to-noise ratio, long-slit spectra of 49 BCGs in thenearby Universe. Here, we derive single stellar population(SSP)-equivalent ages, metallicities and α-abundance ratios in thecentres of the galaxies using the Lick system of absorption lineindices. We systematically compare the indices and derived parametersfor the BCGs with those of large samples of ordinary elliptical galaxiesin the same mass range. We find no significant differences between theindex-velocity dispersion relations of the BCG data and those of normalellipticals, but we do find subtle differences between the derived SSPparameters. The BCGs show, on average, higher metallicity ([Z/H]) andα-abundance ([E/Fe]) values. We analyse possible correlationsbetween the derived parameters and the internal properties of thegalaxies (velocity dispersion, rotation, luminosity) and those of thehost clusters (density, mass, distance from BCG to X-ray peak, presenceof cooling flows), with the aim of dissentangling if the BCG propertiesare more influenced by their internal or host cluster properties. TheSSP parameters show very little dependence on the mass or luminosity ofthe galaxies, or the mass or density of the host clusters. Of thissample, 26 per cent show luminosity-weighted ages younger than 6 Gyr,probably a consequence of recent - if small - episodes of starformation. In agreement with previous studies, the BCGs withintermediate ages tend to be found in cooling-flow clusters with largeX-ray excess.
| Radial kinematics of brightest cluster galaxies
This is the first of a series of papers devoted to the investigation ofa large sample of brightest cluster galaxies (BCGs), their kinematic andstellar population properties, and the relationships between those andthe properties of the cluster. We have obtained high signal-to-noiseratio, long-slit spectra of these galaxies with Gemini and WilliamHerschel Telescope with the primary purpose of investigating theirstellar population properties. This paper describes the selectionmethods and criteria used to compile a new sample of galaxies,concentrating on BCGs previously classified as containing a halo (cDgalaxies), together with the observations and data reduction. Here, wepresent the full sample of galaxies, and the measurement andinterpretation of the radial velocity and velocity dispersion profilesof 41 BCGs. We find clear rotation curves for a number of these giantgalaxies. In particular, we find rapid rotation(>100kms-1) for two BCGs, NGC 6034 and 7768, indicatingthat it is unlikely that they formed through dissipationless mergers.Velocity substructure in the form of kinematically decoupled cores isdetected in 12 galaxies, and we find five galaxies with velocitydispersion increasing with radius. The amount of rotation, the velocitysubstructure and the position of BCGs on the anisotropy-luminositydiagram are very similar to those of `ordinary' giant ellipticals inhigh-density environments.
| 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.
| H-Band and Spectroscopic Properties of A1644
We discuss H-band (1.65 μm) near-infrared photometry of the central 9h-2 Mpc2 of Abell 1644 (A1644) to a limitingMH~M*H+3 (throughout this paper H0=100h km s-1 Mpc-1). There are 861 galaxies in thephotometric survey region. We also measured radial velocities of 155galaxies; 141 of these are cluster members within 2.44 h-1Mpc of the cluster center. The completeness limit of the spectroscopicsurvey is H~13 (MH~M*H). The clustervelocity dispersion of σ~1000 km s-1 remains constantout to the limiting radius. We find no evidence for substructure in thecluster. The cluster mass within R=2.4 h-1 Mpc is7.6+/-1.3×1014 h -1 Msolar. Wecompute the cluster luminosity function; the Schechter parametersα=-1.14+/-0.08 and M*H=-24.3+/-0.2 (withh=0.5) agree well with other H-band luminosity functions. From thevirial theorem and the caustic method we compute one of the firstmass-to-light ratios at H; the result is M/LH=82-127 hMsolar/Lsolar within 1.5 h-1 Mpc. Thisratio corresponds to 374-579 h Msolar/Lsolar at R.The agreement of our IR measurement with previous M/L determinationsindicates that at low redshift dust and young stellar populations mayproduce only negligible systematic errors in optical mass-to-lightratios.
| 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 Southern Sky Redshift Survey
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
| Properties of the ROSAT selected radio sources. I. The sample.
A cross-identification of southern-sky objects with the ROSAT All-SkySurvey and PMN Radio (5 GHz) Survey yields a list of 642 sources.Subsequential optical identification for all these coincidences has beentaken to form a large sample of galaxies and active galactic nuclei. Asa result, 311 (52 %) were previously optically identified asextragalactic objects. The fluxes detected from X-ray, optical, andradio bands for them are compiled.
| 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.
| 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.
| 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.
| 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.
| 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.
| 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.
| The kinematics of dense clusters of galaxies. I - The data
We have measured redshifts in the fields of the 31 R greater than 1Abell clusters with z of 0.02-0.05 and absolute b exp II above 30 deg.At least ten of the fields are severely contaminated by superimposedvelocity peaks. We derive the mean velocities and velocity dispersionsof the 25 dense peaks in the sample. The abundance of peaks, 6.6 x 10exp -6 h-cubed Mpc exp -3, is consistent with the mean number density ofR above 1 Abell clusters. The range of velocity dispersions is 304-1346km/s. The median dispersion is 718 km/s. The subset of eight systemswith cD galaxies has a median velocity dispersion of 792 km/s, close tothat of non-cD systems (626 km/s). When these data are combined with 16cD cluster velocity dispersions from our previous study (Zabludoff etal., 1990, or ZHG) and Dunn (1991), eight of 25 cD galaxies havepeculiar motions larger than half the cluster velocity dispersions.These findings further support the conclusions of Beers and Geller(1983), ZHG, and Dunn (1991), who argue that cD galaxies do not lie inthe global kinematic center, but in local potential minima. If so,systems with speeding cD's are probably a guide to substructure indynamically evolving systems.
| 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.
| Revised coordinates for 373 selected objects in the Southern Galaxy Catalogue
Improved positions have been determined for 373 galaxies listed in theSouthern Galaxy Catalogue of Corwin et al. (1985) as having poorcoordinates. The revised coordinates are expected to be good to 6 arcsec(rms) in each coordinate.
| A catalog of 1268 radial velocities in 15 rich clusters
Abstract image available at:http://adsabs.harvard.edu/abs/1988AJ.....95..284D
| A catalog of morphological types in 55 rich clusters of galaxies
Data are presented from a study of 55 rich clusters of galaxies. Thedata include positions, morphological types, estimated total magnitudes,bulge sizes, and ellipticities for about 6000 galaxies, as determinedfrom high scale photographic plates. Data reduction procedures aredescribed, and a brief analysis of cluster richness, which indicatesthat Abell richness classes are only rough indicators of total clustermembership, is included.
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