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|Study of the Structure of the Coma Cluster Based on a Hierarchical Force Clustering Method|
Six subclusters in the Coma cluster have been selected on the basis of ahierarchical clustering method that takes the gravitational interactionamong galaxies into account. Of these, 3 central subclusters around thegalaxies NGC 4889, NGC 4874, and NGC 4839 have been singled out. We haveused the objective statistical criterion applied by Vennik and Anosovain studies of close groups of galaxies to evaluate each member includedin a subcluster with a high probability. Galaxies with a significantdeficit of hydrogen HI, including objects from the Bravo-Alfaro list,have been identified with members of the subclusters, with the greatestnumber of them in the subclusters around NGC 4874 and NGC 4839. Aquantitative estimate of the hydrogen deficit using the HI index in theRCG3 catalog reveals a statistically significant excess value for thosegalaxies that are members of the subclusters compared to galaxies with ahydrogen deficit in the overall Coma cluster field. A substantial numberof the spiral galaxies with a hydrogen deficit in the subclusters turnedout to be radio galaxies as well.
|1.65-μm (H -band) surface photometry of galaxies - VIII. The near-IR κ space at z =0|
We present the distribution of a statistical sample of nearby galaxiesin the κ -space (κ 1 ~logM , κ 2~logI e 3 M /L , κ 3 ~logM /L ).Our study is based on near-IR (H -band: λ =1.65μm)observations, for the first time comprising early- and late-typesystems. Our data confirm that the mean effective dynamicalmass-to-light ratio M /L of the E+S0+S0a galaxies increases withincreasing effective dynamical mass M , as expected from the existenceof the Fundamental Plane relation. Conversely, spiral and Im/BCDgalaxies show a broad distribution in M /L with no detected trend of M/L with M , the former galaxies having M /L values about twice largerthan the latter, on average. For all the late-type galaxies, the M /Lincreases with decreasing effective surface intensity I e ,consistent with the existence of the Tully-Fisher relation. Theseresults are discussed on the basis of the assumptions behind theconstruction of the κ -space and their limitations. Our study iscomplementary to a previous investigation in the optical (B -band:λ =0.44μm) and allows us to study wavelength dependences ofthe galaxy distribution in the κ -space. As a first result, wefind that the galaxy distribution in the κ 1 -κ2 plane reproduces the transition from bulgeless tobulge-dominated systems in galaxies of increasing dynamical mass.Conversely, it appears that the M /L of late-types is higher (lower)than that of early-types with the same M in the near-IR (optical). Theorigins of this behaviour are discussed in terms of dust attenuation andstar formation history.
|Redshift-Distance Survey of Early-Type Galaxies. I. The ENEARc Cluster Sample|
This paper presents data on the ENEARc subsample of the larger ENEARsurvey of nearby early-type galaxies. The ENEARc galaxies belong toclusters and were specifically chosen to be used for the construction ofa Dn-σ template. The ENEARc sample includes newmeasurements of spectroscopic and photometric parameters (redshift,velocity dispersion, line index Mg2, and the angular diameterdn), as well as data from the literature. New spectroscopicdata are given for 229 cluster early-type galaxies, and new photometryis presented for 348 objects. Repeat and overlap observations withexternal data sets are used to construct a final merged catalogconsisting of 640 early-type galaxies in 28 clusters. Objectivecriteria, based on catalogs of groups of galaxies derived from completeredshift surveys of the nearby universe, are used to assign galaxies toclusters. In a companion paper, these data are used to construct thetemplate Dn-σ distance relation for early-typegalaxies, which has been used to estimate galaxy distances and derivepeculiar velocities for the ENEAR all-sky sample. Based on observationsat Complejo Astronomico El Leoncito, operated under agreement betweenthe Consejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; Cerro Tololo Inter-American Observatory,National Optical Astronomical Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation; the EuropeanSouthern Observatory (ESO), partially under the ESO-ON agreement; theFred Lawrence Whipple Observatory; the Observatório do Pico dosDias, operated by the Laboratório Nacional de Astrofísicaand the MDM Observatory at Kitt Peak.
|The UZC-SSRS2 Group Catalog|
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
|Spectroscopic constraints on the stellar population of elliptical galaxies in the Coma cluster|
Near-infrared spectra for a sample of 31 elliptical galaxies in the Comacluster are obtained. The galaxies are selected to be ellipticals (nolenticulars), with a large spatial distribution, covering both the coreand outskirts of the cluster (i.e. corresponding to regions with largedensity contrasts). COsp (2.3-μm) absorption indices,measuring the contribution from intermediate-age red giant andsupergiant stars to the near-infrared light of the ellipticals, are thenestimated. It is found that the strength of COsp features inelliptical galaxies increases from the core (r<0.2°) to theoutskirts (r>0.2°) of the Coma cluster. Using the Mg2strengths, it is shown that the observed effect is not caused bymetallicity and is mostly caused by the presence of a younger population(giant and supergiant stars) in ellipticals in the outskirts(low-density region) of the cluster. Using the COsp features,the origin of the scatter on the near-infrared Fundamental Plane (therelation between the effective diameter, effective surface brightnessand velocity dispersion) of elliptical galaxies is studied. Correctingthis relation for contributions from the red giant and supergiant stars,the rms scatter reduces from 0.077 to 0.073dex. Although measurable, thecontribution from these intermediate-age stars to the scatter on thenear-infrared Fundamental Plane of ellipticals is only marginal. Arelation is found between the COsp and V-K colours ofellipticals, corresponding to a slope of 0.036+/-0.016, significantlyshallower than that from the Mg2-(V-K) relation. This isstudied using stellar synthesis models.
|1.65 μm (H-band) surface photometry of galaxies. III. observations of 558 galaxies with the TIRGO 1.5 m telescope|
We present near-infrared H-band (1.65 μm ) surface photometry of 558galaxies in the Coma Supercluster and in the Virgo cluster. This dataset, obtained with the Arcetri NICMOS3 camera ARNICA mounted on theGornergrat Infrared Telescope, is aimed at complementing, withobservations of mostly early-type objects, our NIR survey of spiralgalaxies in these regions, presented in previous papers of this series.Magnitudes at the optical radius, total magnitudes, isophotal radii andlight concentration indices are derived. We confirm the existence of apositive correlation between the near-infrared concentration index andthe galaxy H-band luminosity Based on observations taken at TIRGO(Gornergrat, Switzerland). TIRGO is operated by CAISMI-CNR, Arcetri,Firenze, Italy. Tables 1 and 2 are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|1.65 μm (H-band) surface photometry of galaxies. V. Profile decomposition of 1157 galaxies|
We present near-infrared H-band (1.65 μm) surface brightness profiledecomposition for 1157 galaxies in five nearby clusters of galaxies:Coma, A1367, Virgo, A262 and Cancer, and in the bridge between Coma andA1367 in the ``Great Wall". The optically selected (mpg≤16.0) sample is representative of all Hubble types, from E to Irr+BCD,except dE and of significantly different environments, spanning fromisolated regions to rich clusters of galaxies. We model the surfacebrightness profiles with a de Vaucouleurs r1/4 law (dV), withan exponential disk law (E), or with a combination of the two (B+D).From the fitted quantities we derive the H band effective surfacebrightness (μe) and radius (re) of each component, theasymptotic magnitude HT and the light concentration indexC31. We find that: i) Less than 50% of the Ellipticalgalaxies have pure dV profiles. The majority of E to Sb galaxies is bestrepresented by a B+D profile. All Scd to BCD galaxies have pureexponential profiles. ii) The type of decomposition is a strong functionof the total H band luminosity (mass), independent of the Hubbleclassification: the fraction of pure exponential decompositionsdecreases with increasing luminosity, that of B+D increases withluminosity. Pure dV profiles are absent in the low luminosity rangeLH<1010 L\odot and become dominantabove 1011 L\odot . Based on observations taken atTIRGO, Gornergrat, Switzerland (operated by CAISMI-CNR, Arcetri,Firenze, Italy) and at the Calar Alto Observatory (operated by theMax-Planck-Institut für Astronomie (Heidelberg) jointly with theSpanish National Commission for Astronomy). Table 2 and Figs. 2, 3, 4are available in their entirety only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|The near-infrared Fundamental Plane of elliptical galaxies|
Near-infrared (2.2 μm) observations of a sample of 48 ellipticalgalaxies in the Coma cluster have been carried out and used to study thenear-infrared Fundamental Plane (FP) of ellipticals in this cluster. Anrms scatter of 0.072 dex is found for this relation, similar to that ofits optical counterpart, using the same sample of galaxies. Thiscorresponds to an uncertainty of 18 per cent in distances to individualgalaxies derived from this relation. The sensitivity of thenear-infrared FP to the star formation or changes in metallicity andstellar population among the ellipticals is explored and found to besmall, although a likely source of scatter in this relation iscontributions from the asymptotic giant branch (AGB) population to thenear-infrared light. Allowing for observational uncertainties, we findan intrinsic scatter of 0.060 dex in the near-infrared FP. The clustergalaxies presented here provide the zero-point for the peculiar velocitystudies, using the near-infrared FP. Changes in the slopes of theD-sigma and L-sigma relations of ellipticals between the optical andnear-infrared wavelengths are investigated and found to be due tovariations in metallicity or age (or a combination of them). However, itis not possible to disentangle the effects of age and metallicity inthese relations. We find M/L~M^alpha with alpha=0.18+/-0.01 in thenear-infrared and alpha=0.23+/-0.01 at optical wavelengths, using thesame sample of galaxies. This relation is interpreted as being due to amass-metallicity effect or changes in age or the initial mass functionslope with mass. Using evolutionary population synthesis models, we findthat the effects of age and metallicity decouple in the (M/L)_K versusMg_2 and (M/L)_K versus (V-K) diagrams. The models suggest that theobserved trends in these relations may be due to an age sequence, whilemetallicity mainly contributes to the scatter.
|The tilt of the Fundamental Plane of early-type galaxies: wavelength dependence|
The photometric parameters R_e and mu_e of 74 early-type (E+S0+S0a)galaxies within 2 deg projected radius from the Coma cluster centre arederived for the first time in the near-infrared H band (1.65 μm).These are used, coupled with measurements of the central velocitydispersion sigma found in the literature, to determine the H-bandFundamental Plane (FP) relation of this cluster: logR_e~Alogsigma+bmu_e. The same procedure is applied to previouslyavailable photometric data in the BVrIK bands, to perform amultiwavelength study of the FP relation. Because systematicuncertainties in the value of the FP parameters are introduced both bythe choice of the fitting algorithm used to derive the FP template, andby the presence of statistical biases connected with the sampleselection procedure, we emphasize the importance of deriving the FPparameters in the six different photometric bands using an identicalfitting algorithm, and appropriate corrections to eliminate the effectsof sample incompleteness. Once these corrections are applied, we findthat the FP b coefficient is stable with wavelength (~0.35+/-0.02),while the A coefficient increases significantly with increasingwavelength: from ~1.35 to ~1.70 (+/-0.1) from the optical to theinfrared, in agreement with an earlier result presented recently byPahre and Djorgovski. Therefore the slope of the FP relation, althoughchanging with wavelength, never approaches the virial theoremexpectation A=2.0 when the central velocity dispersion only is used tobuild the FP. We also find that the magnitude of the slope change can beentirely explained by the presence of the well-known relation betweencolour and magnitude among early-type galaxies. We conclude that thetilt of the Fundamental Plane is significant, and must be the result ofsome form of broken homology among early-type galaxies, while itswavelength dependence derives from whatever mechanism (currently thepreferred one is the existence of a mass-metal content sequence)produces the colour-magnitude relation in those galaxies.
|The Universality of the Fundamental Plane of E and S0 Galaxies: Spectroscopic Data|
We present central velocity dispersion measurements for 325 early-typegalaxies in eight clusters and groups of galaxies, including newobservations for 212 galaxies. The clusters and groups are the A262,A1367, Coma (A1656), A2634, Cancer, and Pegasus Clusters and the NGC 383and NGC 507 Groups. The new measurements were derived frommedium-dispersion spectra that cover 600 Å centered on the Mg I btriplet at lambda ~ 5175 Å. Velocity dispersions were measuredusing the Tonry & Davis cross-correlation method, with a typicalaccuracy of 6%. A detailed comparison with other data sources is made.
|The Universality of the Fundamental Plane of E and S0 Galaxies: Sample Definition and I-Band Photometric Data|
As part of a project to compare the fundamental plane and Tully-Fisherdistance scales, we present here I-band CCD photometry for 636early-type galaxies in eight clusters and groups of galaxies. These arethe A262, A1367, Coma (A1656), A2634, Cancer and Pegasus Clusters, andthe NGC 383 and NGC 507 Groups. Sample selection, cluster properties,and cluster membership assignment criteria are discussed. We presentphotometric parameters that are used in the fundamental plane relation,the effective radius r_e, and the effective surface brightness mu_e, asderived from a r^1/4 fit to the observed radial photometric profile ofeach galaxy. A comparison with similar data found in the literature forthe Coma Cluster shows that large systematic uncertainties can beintroduced in the measurement of r_e and mu_e by the particular methodused to derive those parameters. However, the particular combination ofthese two parameters that enters in the fundamental plane relation is aquantity that can be measured with high accuracy.
|A catalogue of Mg_2 indices of galaxies and globular clusters|
We present a catalogue of published absorption-line Mg_2 indices ofgalaxies and globular clusters. The catalogue is maintained up-to-datein the HYPERCAT database. The measurements are listed together with thereferences to the articles where the data were published. A codeddescription of the observations is provided. The catalogue gathers 3541measurements for 1491 objects (galaxies or globular clusters) from 55datasets. Compiled raw data for 1060 galaxies are zero-point correctedand transformed to a homogeneous system. Tables 1, 3, and 4 areavailable in electronic form only at the CDS, Strasbourg, via anonymousftp 22.214.171.124. Table 2 is available both in text and electronic form.
|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.
|Abell 2199 and Abell 2634 revisited|
Previous D_n-sigma work found surprisingly large negative peculiarvelocities for Abell 2199 and Abell 2634. In order to assess theseresults independently we have made new spectroscopic and photometricobservations. We report 141 new redshift, velocity dispersion (sigma)and Mg_2 index measurements, and photometry for 79 early-type galaxies.Special attention has been paid to linking the new sigma measurements onto a standard system that minimizes systematic errors. While the Abell2199 sigma measurements are in good agreement with our previouslyreported FLEX values, for Abell 2634 galaxies the new sigmas aresystematically lower. The FLEX measurements for some Abell 2634 galaxiesappear to have been erroneous due to a smearing problem with the CCDdetector. The new photometric data are in excellent agreement withpreviously reported values. We also present a new compilation of datafor 72 early-type Coma cluster galaxies. Assuming that the Coma clusterlies at rest with respect to the cosmic microwave background frame, wederive peculiar velocities of -160+/-380 and -670+/-490 km s^-1 forAbell 2199 and Abell 2634 respectively. We estimate that the likelysystematic errors on these measurements are less than 200kms^-1. Thederived peculiar velocities are considerably less than previousestimates and are not significantly different from zero.
|The Butcher-Oemler Effect at Low Redshift: Spectroscopy of Five Nearby Clusters of Galaxies|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113..492C&db_key=AST
|The Relative Distance Between the Clusters of Galaxies A2634 and Coma|
The Tully-Fisher (TF) and Fundamental Plane (FP) relations are used toobtain two independent estimates of the relative distance between theclusters A2634 and Coma. Previously published studies of A2634 showed alarge discrepancy between the distance estimates obtained with the TFand the \dns\ relations, questioning the reliability ofredshift-independent distances obtained using these relations. Becauseof the importance of this issue, we have obtained new distance estimatesfor A2634, based on much larger samples than previously used, andselected according to rigorous membership criteria. New I band CCDphotometry for 175 galaxies, new 21 cm observations of 11 galaxies, andnew velocity dispersion measurements for 62 galaxies are used togetherwith previously published data in building these samples. As part of alarger project to compare the TF and FP distance-scales, we haveobtained a new FP template using for the first time I band photometry.The template is derived using a sample of 109 E and S0 galaxies that aremembers of the Coma cluster. Its parameters are in very good agreementwith recent determinations of the FP obtained at shorter wavelengths.The uncertainty with which the FP can provide peculiar velocityestimates for single galaxies is =~ 0.43 mag in the distance modulus, or20% of the distance. This uncertainty is slightly larger than thetypical uncertainty that characterizes TF estimates. However thisdisadvantage is partly compensated by the fact that the sampleincompleteness bias has a less severe effect on FP cluster distanceestimates than it has on the corresponding TF distance estimates. Also,cluster membership is more readily established for early-type objectsthan for spirals. After the appropriate corrections for sampleincompleteness have been taken into account, we find the TF and FPdistance estimates to be in good agreement, both indicating that A2634has a negligibly small peculiar velocity with respect to the CosmicMicrowave Background reference frame. Because of the high accuracy withwhich the two distance estimates have been obtained, their agreementstrongly supports the universality of the TF and FP relations, andtherefore their reliability for the estimate of redshift-independentdistances.
|The fundamental plane of early-type galaxies: stellar populations and mass-to-light ratio.|
We analyse the residuals to the fundamental plane (FP) of ellipticalgalaxies as a function of stellar-population indicators; these are basedon the line-strength parameter Mg_2_ and on UBVRI broad-band colors, andare partly derived from new observations. The effect of the stellarpopulations accounts for approximately half the observed variation ofthe mass-to-light ratio responsible for the FP tilt. The residual tiltcan be explained by the contribution of two additional effects: thedependence of the rotational support, and possibly that of the spatialstructure, on the luminosity. We conclude to a constancy of thedynamical-to-stellar mass ratio. This probably extends to globularclusters as well, but the dominant factor would be here the luminositydependence of the structure rather than that of the stellar population.This result also implies a constancy of the fraction of dark matter overall the scalelength covered by stellar systems. Our compilation ofinternal stellar kinematics of galaxies is appended.
|A Catalog of Stellar Velocity Dispersions. II. 1994 Update|
A catalog of central velocity dispersion measurements is presented,current through 1993 September. The catalog includes 2474 measurementsof 1563 galaxies. A standard set of 86 galaxies is defined, consistingof galaxies with at least three reliable, concordant measurements. It issuggested that future studies observe some of these standard galaxies sothat different studies can be normalized to a consistent system. Allmeasurements are reduced to a normalized system using these standards.
|Automated surface photometry for the Coma Cluster galaxies: The catalog|
A homogeneous photometry catalog is presented for 450 galaxies withB25.5 less than or equal to 16 mag located in the 9.8 deg x9.8 deg region centered on the Coma Cluster. The catalog is based onphotographic photometry using an automated surface photometry softwarefor data reduction applied to B-band Schmidt plates. The catalogprovides accurate positions, isophotal and total magnitudes, major andminor axes, and a few other photometric parameters including rudimentarymorphology (early of late type).
|Galaxy Properties at the North Galactic Pole. I. Photometric Properties on Large Spatial Scales|
A two-color study of the galaxies detected on POSS-I in a 289 squaredegree region centered on the North Galactic Pole is presented. We use avariety of mapping techniques to characterize the large-scale spatialdistribution of galaxies. The depth and sample size of this new surveyallows, for the first time, the isolation of large photometricsubsamples of galaxies in high- and low-density environments on thescale of superclusters. Our principal finding is a statisticallysignificant difference between the mean photometric properties of thesesubsamples in the sense that galaxies in the high-density Coma andfilament environments have redder colors and larger concentrationindices than galaxies drawn from low-density interfilament regions.These results are in accord with the known morphology-density relation.Thus, appropriately chosen photometric and morphological parameters, inconcert with a galaxy surface density map, can be used to selectstructures from the projected galaxy distribution which correspond toregions of high density. An illustration of this point is our discoveryof a concentration of blue galaxies identified in our maps near the coreof the Coma cluster. This feature is comprised of early-type galaxieswhich exhibit signs of current or recent star formation. These resultsare predicated on relations between morphological type and photometricparameters derived from APS scans of POSS-I. We therefore discuss theimage calibration procedures used to compile our catalog of physicallysignificant photometric parameters. We demonstrate the morphologicaltype dependence among quantities such as mean color and imageconcentration index, and the lack of such a dependence for mean surfacebrightness.
|The environmental dependence of the Mg2 correlations for elliptical galaxies|
New measurements of Mg2 for Coma cluster ellipticals were made in orderto assess the level of any environmental dependence in the fundamentalrelationships of early-type galaxies, with emphasis on ellipticals thatlie in the outer areas of the cluster. The sigma-Mg2 and D-Mg2 relationsare compared for ellipticals located in the inner region of the clusterand in the cluster halo. It is shown that the Mg2 correlations possess asmall environmental effect. From the sigma-Mg2 relation, it is foundthat halo ellipticals have, on average, for a given sigma, Mg2 lower by0.017 +/-0/005 mag compared to inner ellipticals. A similar effect isobserved in the D-Mg2 relation. At a fixed D, ellipticals in the clusterhalo have, on average, Mg2 lower by 0.025 +/-0.008 mag. The possibilitythat the observed offsets in the sigma-Mg2 and D-Mg2 relations arecaused by star formation continuing to a more recent epoch in haloellipticals is also investigated.
|New D-sigma results for Coma cluster ellipticals|
A total of 51 ellipticals in the Coma cluster are described in terms ofphotometric diameters (Ds) and velocity dispersions (sigmas) to evaluatethe environmental dependence of the D-sigma relation. Observations aredescribed of the ellipticals in the outer part of the cluster as well assome from the central region based on spectra between 4800-5600 A.Aperture photometry is employed to derive effective diameter, effectivesurface brightness, and photometric diameter. The zero point of theD-sigma relation varies very little from the Coma core, and the outerellipticals possess somewhat larger Ds at fixed values of sigma. TheD-sigma relation is considered a robust indicator with nosurface-brightness bias, and the sample indicates that planes defined bythe Virgo and Coma clusters are not fundamentally different.
|Galaxy redshift survey in a narrow strip crossing the Coma cluster|
A list of galaxies brighter than 18m with the coordinates in the rangeRA = (10h42m, 15h28m), Dec. = (+ 28 deg 10 min, + 28 deg 20 min) ispresented. The list contains data on apparent photographic magnitude,angular diameter, axial ratio, and radial velocity for more than 300objects. Emission and absorption line galaxies found show an essentiallydifferent character in their spatial distribution.
|The surface brightness test for the expansion of the universe. II - Radii, surface brightness, and absolute magnitude correlations for nearby E galaxies|
Data for elliptical galaxies in the Virgo, Fornax, and Coma clusters andin the general field are analyzed in order to determine the dispersionin average surface brightness. The data are discussed using measures ofboth the effective radius and the Petrosian r(eta) radii. The dispersionis found to be about 0.5 mag after reducing the data to absolutemagnitude M(B) = -22. This value is smaller than the 1.8 mag Tolman (1 +z) exp 4 factor, even at the modest redshift of z = 0.5, showing thatthe Tolman test is feasible in practice as well as in principle.
|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.
|Cross identification of 238 galaxies and use of a colour magnitude relation in the coma cluster|
A catalog of 238 galaxies is obtained by the cross identification ofdata from Kent and Gunn (1982), Godwin and Peach (1977) and Godwin etal. (1983). It contains the radial velocities, bvr magnitudes, colorindices, isophotal radii, and other characteristics of individualgalaxies. This leads to the definition of various samples of radialvelocities complete to various limiting magnitudes depending on radius.The use of a color magnitude relation is discussed to define a class of1340 objects likely to belong to the cluster from their photometry only.
|The structure of brightest cluster members. II - Mergers|
Surface photometry of 342 bright elliptical galaxies in 103 clusters isanalyzed for evidence of mergers. Structural differences betweenbrightest cluster members (BCMs) and normal ellipticals can besummarized as having enlarged characteristic radii and shallow profileslopes (beta greater than -1.7). Profile morphology criteria for theelliptical types gE, D, and cD are outlined. Comparison of observationswith numerical simulations of mergers strongly suggests a past historyof dynamical growth for BCMs. Weak correlations of global clusterproperties to BCMs supports the hypothesis proposed by Merritt (1984)that mergers are important in early subgroups before virialization andformation of a cluster identity.
|The Coma Cluster - Part One - a Catalogue of Magnitudes Colours Ellipticities and Position Angles for 6724 Galaxies in the Field of the Coma Cluster|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983MNRAS.202..113G&db_key=AST
|The dynamics of rich clusters of galaxies. I - The Coma cluster|
Self-consistent analytical dynamical models are used to study theendpoint of cluster formation, concentrating on the Coma cluster.Particular attention is paid to the effects of anisotropy in thevelocity dispersion and variations in the energy-distribution functionon the cluster structure, the effect on the core structure of a massivecentral object, the dynamical consequences of morphological segregation,cosmological infall and the edge of a cluster, the distribution of darkmatter in a cluster, and the implications of X-ray observations for thedistribution of gravitating material in a cluster. Radial velocity datais displayed, and new and repeated redshifts are reported for a numberof galaxies in the central regions of the cluster. Cluster membership isdetermined and a velocity-dispersion profile is derived. A compositesurface-density profile is derived, and amazing examples are shown ofmodels with virtually identical surface-density profiles but otherwisecompletely different internal dynamics.
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