Cluster Velocity Dispersion Research Articles

The Distribution of Bright Galaxies

Following a brief review of the early developments in the field, we discuss a few new advances in the distribution of bright galaxies which occured after the extensive review paper by Oort (1983) We show that the large scale structure, shells, filaments and/or sheets, may bias the determination of the velocity dispersion in clusters of galaxies and that the boundaries of the voids may often be biassed by the clusters and groups velocity dispersion.Of interest are the very large structures selected on catalogs of clusters of galaxies. The “Local Structure” claimed by Tully seems to be somewhat flattened and about parallel to the plane of the Local Supercluster. If the structure is real the alignement is relevant in relation to the physical mechanisms at work at the time of formation. Noticeable progress has been done in the measurement of the large scale velocity field. Large scale motions may somewhat bias the study of the topology of the Universe.Relevant work has be done on the shape of the boundaries of the voids and observational work is progressing to detect faint galaxies in voids and determine their charactestics. This is important also in relation to the theory of biassed galaxy formation. To better focus the observational problem and eventually related biasses, we give some statistics on dwarf galaxies in the Virgo cluster.

An Upper Limit on the Masses of Galaxies in Clusters

Clusters of galaxies are believed to be dominated by dark matter. Some of this matter is presumably bound to galaxies in the form of massive halos, while the rest moves freely in the cluster potential well. The exact fraction of dark matter bound to galaxies is an important datum for models of cluster evolution, since time scales for orbital decay, merging, stripping, etc. are sensitive functions of galaxy mass. In this study we attempt to put a firm upper limit on the amount of dark matter associated with galaxies in clusters, by calculating the response of a galaxy with an initially massive halo to the mean tidal field produced by the overall cluster potential well. If the velocity dispersions of galactic halos are roughly equal to those of luminous galaxies, σg, it is easy to show that the truncated mass of a spherical galaxy orbiting near the center of a cluster is roughly mg ≈ G−1σg3σc−1Rc ≈ 4 × 1011M⊙, where σc and Rc are the cluster velocity dispersion and core radius. The precise value of mg must depend on the orbital geometry, as well as the number of pericenter passages since cluster formation, among other factors.

Existence And Nature Of Dark Matter In The Universe

Ann. Rev. Astron. Astrophys. 1987. 25: 425-72 Copyright © 1987 by Annual Reviews Inc. All rights reserved EXISTENCE AND NATURE OF DARK MATTER IN THE UNIVERSE Virginia T rimble Astronomy Program, University of Maryland, College Park, Maryland 20742, and Department of Physics, University of California, Irvine, California 92717 1. HISTORICAL INTRODUCTION AND THE SCOPE OF THE PROBLEM The first detection of nonluminous matter from its gravitational effects occurred in 1844, when Friedrich Wilhelm Bessel announced that several decades of positional measurements of Sirius and Procyon implied that each was in orbit with an invisible companion of mass comparable to its own. The companions ceased to be invisible in 1862, when Alvan G. Clark turned his newly-ground 18%” objective toward Sirius and resolved the 10q‘ of the photons from the system emitted by the white dwarf Sirius B. Studies of astrometric and single-line spectroscopic binaries are the modern descendants of Bessel’s work. A couple of generations later, data implying nonluminous matter on two very different scales surfaced almost simultaneously. First, Oort (498, 499) analyzed numbers and velocities of stars near the Sun and concluded that visible stars fell shy by 30-50% of adding up to the amount of gravitating matter implied by the velocities. Then, in 1933, Zwicky (777) concluded that the velocity dispersions in rich clusters of galaxies required 10 to 100 times more mass to keep them bound than could be accounted for by the luminous galaxies themselves. The former result was taken much more seriously than the latter by contemporary and succeeding astronomers (being dignified by the name “the Oort limit”), which is perhaps more a statement about the personalities of Oort and Zwicky than about anything else. 425 0066-4146/87/0915—0425$02.00 © Annual Reviews Inc. - Provided by the NASA Astrophysics Data System

Relaxation and tidal stripping in rich clusters of galaxies. III - Growth of a massive central galaxy

The rate at which a massive galaxy (''cannibal'') grows by capturing other galaxies at the center of a rich, relaxed cluster is calculated. It is shown that the orbital decay preceding capture tends to leave the distribution of orbital velocities isotropic. As a result, most captures occur from nearly radial orbits, and relatively few from circular orbits. The capture rate is initially very low, due to the paucity of low-velocity galaxies, and to the fact that orbital decay times are comparable to a Hubble time. Encounters between galaxies further inhibit their orbital decay; this effect is important when the fraction of a cluster's mass that is bound to galaxies exceeds approx.15%. Assuming that less than approx.20% of a cluster's mass is attached to galaxies, and that the cluster velocity dispersion exceeds approx.500 km s/sup -1/, the typical rate of growth of a central galaxy by capture is rather small, amounting to somewhat less than 1 L* in a cluster lifetime. It is suggested (as in a previous paper) that most cD galaxies formed relatively rapidly, during the collapse and virialization of compact groups or poor clusters, and not during the quieter postcollapse stages as previous authors have advocated. The peculiarmore » object V Zw 311 may be an example of a cD galaxy that is presently forming in this way. Subject headings: clustering-galaxies: evolution-galaxies: structure« less

Structural parameters and masses for three old LMC clusters

view Abstract Citations (35) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Structural parameters and masses for three old LMC clusters. Elson, R. A. W. ; Freeman, K. C. Abstract Luminosity profiles are presented for three old LMC clusters, NGC 1835, NGC 2210, and NGC 2257. King models are fitted to the profiles, the core and tidal radii are determined, and the total mass of each cluster is deduced. Total luminosities and mass-to-light ratios are also derived. For NGC 1835 a dynamical mass is determined from the cluster's velocity dispersion, obtained from a spectrum of its integrated light. Lower limits on tidal mass-to-light ratios are 0.18 + or 0.03, 0.11 + or - 0.02, and 0.56 + or - 0.09 for NGC 1835, NGC 2210, and NGC 2257, respectively. The velocity dispersion measurement yields a mass-to-light ratio for NGC 1835 of 0.42 + or - 0.08. These values are up to 3 times larger than previous determinations. The values for NGC 1835 and NGC 2210 are still somewhat smaller than mass-to-light ratios of Milky Way globulars or of NGC 2257, and it is suggested that this reflects a difference in age. Publication: The Astrophysical Journal Pub Date: January 1985 DOI: 10.1086/162817 Bibcode: 1985ApJ...288..521E Keywords: Galactic Structure; Globular Clusters; Magellanic Clouds; Mass To Light Ratios; Stellar Evolution; Astronomical Photometry; Milky Way Galaxy; Power Spectra; Astrophysics full text sources ADS | data products SIMBAD (4) NED (1)

Rotational Field and Velocity Dispersion in Globular Clusters: ω CEN and 47 TUC

Thanks to numerous and accurate radial velocity measurements obtained with CORAVEL, the rotational velocity fields, the spatial velocity dispersions from the centre to the edge and the ordered to random motions ratios are deduced for two globular clusters: ω Cen and 47 Tuc. Masses through virial theorem and M/L ratios are also given. A more comprehensive study will be published in Astron. & Astrophys.

The A2197 and A2199 galaxy clusters

view Abstract Citations (78) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The A2197 and A2199 Galaxy Clusters Gregory, S. A. ; Thompson, L. A. Abstract New redshifts are presented for 74 galaxies in and near the rich clusters A2197 and A2199. When added to results in the literature, the authors have a total sample of 136 galaxies with known redshifts in the region. They determine the systematic redshift and line-of-sight velocity dispersions for both clusters. By applying the virial theorem they find mass-to-light (M/L) ratios for each cluster core in the range 200 - 400. The authors model the binary cluster with a two-body infall analysis and thereby determine an independent estimate for the M/L ratio of the entire system. Surprisingly, the double cluster method indicates that M/L < 100. Publication: The Astrophysical Journal Pub Date: November 1984 DOI: 10.1086/162617 Bibcode: 1984ApJ...286..422G Keywords: Galactic Clusters; Galactic Structure; Mass To Light Ratios; Red Shift; Astronomical Maps; Astronomical Models; Luminosity; Astrophysics full text sources ADS | data products SIMBAD (139) NED (113) Related Materials (1) Erratum: 1986ApJ...305..580G

The velocity dispersion of the globular clusters in the Fornax dwarf galaxy

The velocity dispersion of the globular clusters in the Fornax dwarf galaxy

21 centimeter observations of supercluster galaxies - The bridge between Coma and A1367

view Abstract Citations (46) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS 21 CM observations of supercluster galaxies : the bridge between Comaand A 1367. Chincarini, G. L. ; Giovanelli, R. ; Haynes, M. P. Abstract The authors present 21 cm observations of galaxies in the region of the Coma-A1367 supercluster. It is shown that galaxies near the cluster center are hydrogen deficient while galaxies which are in between the two clusters have a normal hydrogen content. A crossing time of about 1.7×109 yr is defined by the radius of the region of transition between deficient and nondeficient galaxies and the cluster's velocity dispersion. The gas removed by stripping is a small fraction of the gas observed in the X-ray region. Publication: The Astrophysical Journal Pub Date: June 1983 DOI: 10.1086/161014 Bibcode: 1983ApJ...269...13C Keywords: Centimeter Waves; Galactic Clusters; Galactic Evolution; Interstellar Gas; Radio Astronomy; Hydrogen; Spiral Galaxies; X Ray Astronomy; Astrophysics full text sources ADS | data products NED (87) SIMBAD (79)

The dynamics of rich clusters of galaxies. II - The Perseus cluster

The dynamics of the Perseus cluster are analyzed using self-consistent equilibrium analytical models. Using existing data in the literature plus new radial velocities reported here, composite surface density and velocity dispersion profiles are derived. These profiles have been compared with dynamical models described by Kent and Gunn (1982). The best fit suggest the presence of a significant degree of anisotropy in the velocity distribution: galaxy orbits are constrained to pass within a radius of seven cluster radii, or 1.3 deg of the cluster center. For Hubble constant = 50, a core radius of 340 kpc 11 arcmin and a mass to visual light ratio M/L = 300 are found. Using these results, X-ray observations of the intracluster medium in Perseus are reanalyzed. A previously noted discrepancy between the observed temperature of the hot gas and the cluster velocity dispersion is reduced but not eliminated. A cooling accretion flow previously deduced to exist in this cluster is shown to extend to only about one-third of the cluster radius.

Dynamical constraints on star formation efficiency

Dynamical constraints are placed on the local star formation efficiency during the formation of star clusters. Virial models are used to examine the expected changes in cluster velocity dispersion, density, and radius during the period when the gas not converted into stars is removed from the system. Comparison of observed initial and final states of open clusters indicate local efficiencies of about 30 percent if the gas dispersal is slow relative to the dynamical crossing time and 55 percent if the gas loss is rapid. Efficiencies are somewhat dependent on support mechanisms of moleclar clouds, but it is argued that observations of young clusters are in accord with the assumptions of the models used here.

Coma-type radio halos and cluster X-ray morphology

It is pointed out that there seems to be a characteristic X-ray morphology for clusters with Coma-type radio halos. This correlation may be the first evidence that the conditions conducive to formation of a radio halo influence or are influenced by the thermal gas distribution. It is suggested that heating of the intracluster gas by the cosmic rays that power the radio halo may be the source of the correlation. The anomalous gas temperature of Coma may be the result of this process. Future observations of cluster temperatures and velocity dispersions should provide a test of the cosmic-ray heating hypothesis

The correlation between X-ray luminosity and velocity dispersion in clusters of galaxies

view Abstract Citations (112) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The correlation between X-ray luminosity and velicity dispersion in clusters of galaxies. Quintana, H. ; Melnick, J. Abstract The X-ray luminosity-velocity dispersion correlation for 42 clusters is analyzed for which velocity dispersion and either HEAO-1 A-2 fluxes and/or Einstein luminosities are available. The relations between X-ray luminosity, velocity dispersion, and central surface density expected for a thermal bremsstrahllung model are generalized by relaxing some of the mathematical and physical constraints. It is found that there is a strong correlation between X-ray luminosity and velocity dispersion that agrees well with the one expected if the X-rays come from a hot isothermal gas bound to the clusters. Since a correlation is predicted between the central surface density and the X-ray luminosity of clusters, a strong correlation is also expected between the morphological-type populations in the central regions and the velocity dispersions. Publication: The Astronomical Journal Pub Date: July 1982 DOI: 10.1086/113179 Bibcode: 1982AJ.....87..972Q Keywords: Galactic Clusters; Galactic Radiation; Heao; Luminosity; Velocity Distribution; X Ray Sources; Density Distribution; Galactic Structure; Radial Velocity; Red Shift; Astrophysics; Clusters of Galaxies:Velocity Dispersions; Clusters of Galaxies:X-Ray Luminosities full text sources ADS | data products SIMBAD (42) NED (42)

On the Determination of Velocity Dispersions for CD Clusters of Galaxies

view Abstract Citations (111) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the determination of velocity dispersions for cD clusters of galaxies. Quintana, H. ; Lawrie, D. G. Abstract The widely held belief that cD galaxies lie at the kinematical centers of their parent clusters is examined in detail. We find this assumption to be supported by a statistical analysis of all available velocity data. Such an assumption enables us to obtain a direct measure of the true mean velocity of the cluster. The difference between the cD velocity and the mean velocity of the galaxy sample provides a good statistical indication of how well a particular sample represents its parent cluster. For small galaxy samples which poorly represent their parent clusters, we show that the uncertainties in the velocity dispersion have been previously underestimated. A new estimate of the velocity dispersion can be made using the available galaxy sample, but with the cD velocity taken to be the true cluster mean. However, for those clusters with highly unrepresentative samples, this procedure is unlikely to result in an improved estimate of the velocity dispersion. We discuss some individual clusters and consider the extension of the above hypothesis to clusters which contain dumbbell galaxies, D galaxies, or dominant binary galaxies. We show that dumbbell clusters are also dynamically dominated by the corresponding central galaxies. However, for D or binary clusters the evidence is less conclusive. Publication: The Astronomical Journal Pub Date: January 1982 DOI: 10.1086/113080 Bibcode: 1982AJ.....87....1Q full text sources ADS | data products SIMBAD (28)

The relation between velocity dispersion and central galaxy density in clusters of galaxies

A correlation between cluster velocity dispersion and average central galaxy density is reported. The correlation covers the range from rich clusters to small groups of galaxies, or, in terms of velocity dispersion, from v sub r approximately 1500 to approximately 100 km/s. This result is useful for estimating unknown velocity dispersions in clusters with the aid of the relatively easily determined 0.5 Mpc central galaxy density parameter. When combined with the virial theorem, the above relation also suggests that the mass-to-light ratio of galaxy systems increases with the system's velocity dispersion.

Velocity dispersions for X-ray-emitting clusters of galaxies

Combining spectroscopy for five clusters of galaxies reported to contain X-ray sources with previously published data for 21 X-ray clusters, suggested correlations between the cluster's velocity dispersions and their X-ray properties have been tested. Unlike previous investigations, it is found that, for all reasonable data subsets, the cluster radial velocity dispersions sigma(r) are correlated with the cluster X-ray luminosities L/x/ at a confidence level exceeding 99%. The best-fit slope of the (log sigma/r/, log L/x/)-relation is somewhat larger than theoretically predicted, but accurate determination of that relation requires further X-ray and optical observations. For the 'most reliable' data subsample a correlation between sigma(r) and the X-ray source temperatures is also found but at a much lower confidence level (85%) than derived by previous investigators from smaller samples.

Velocity Dispersions in Clusters of Galaxies

31 redshifts have been obtained for A1367, 34 for A262 and 61 for the Centaurus cluster (HMS 1247-4102). Full details of this work have been and will be presented in M.N.R.A.S. Both A1367 and A262 are spiral-rich in Oemler’s classification, while Centaurus is intermediate in type between spiral-rich and poor. In all 3 cases, the distributions of E and L galaxies are centrally concentrated, whilst the spirals are distributed in a more extensive and ragged fashion. The mean corrected redshifts and velocity dispersions for 2 morphological subsets are given in Table I. There is no significant difference in the mean velocities of the 2 subsets for each cluster. However, the velocity dispersions for the spirals are significantly greater than those for the E,L galaxies in both A1367 and A262. The differences in velocity dispersions of the 2 subsets for Centaurus are not statistically significant. Gott and Gunn have suggested that irregular clusters of the sort presently described have not undergone collapse. However, all 3 clusters show morphological separation and are x-ray sources. This is consistent with a collapsed core surrounded by a shell of infailing spirals.

Velocity dispersions for X-ray clusters of galaxies

Five velocity dispersions are presented for x-ray clusters, three of them previously unpublished. Using all available velocity dispersions for x-ray clusters, we analyze with a Monte Carlo model the significance of the observed correlation between velocity dispersion and x-ray luminosity. If A2255 is assumed to be one cluster, a correlation exists at approximately the 2.4 sigma confidence level. If A2255 is actually two clusters, no significant correlation exists. (AIP)

Accretion by galaxy clusters and the relationship between X-ray luminosity and velocity dispersion

view Abstract Citations (101) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Accretion by galaxy clusters and the relationship between X-ray luminosity and velocity dispersion. Silk, J. Abstract A relationship between X-ray luminosity and cluster velocity dispersion is derived, which improves on the results of Solinger and Tucker (1972) in several important respects, and a simple model for primordial gas accretion by a cluster of galaxies is described. It is argued that the accreted gas may be causally related to the occurrence of a central active radio or giant cD or galaxy in X-ray clusters. Accretion and subsequent dissipation lead to a decrease with time in the amount of hot gas and in the X-ray luminosity as well as to an increase in mass of the dominant central galaxy. Publication: The Astrophysical Journal Pub Date: September 1976 DOI: 10.1086/154645 Bibcode: 1976ApJ...208..646S Keywords: Galactic Clusters; Luminous Intensity; X Ray Sources; Astronomical Models; High Temperature Gases; Radial Velocity; Velocity Distribution; X Rays; Astrophysics full text sources ADS | data products NED (10)

Relationship Between X-Ray Luminosity and Velocity Dispersion in Clusters of Galaxies

Relationship Between X-Ray Luminosity and Velocity Dispersion in Clusters of Galaxies