Showing papers on "Brightest cluster galaxy published in 1989"

A Catalog of Rich Clusters of Galaxies

Abstract: This is an all-sky catalog of 4073 rich clusters of galaxies, each having at least 30 members within the magnitude range m3 to m3 +2 (m3 is the magnitude of the third brightest cluster member) and each with a nominal redshift less than 0.2. The southern data have been collected from a survey of UK 1.2 m Schmidt telescope IIIa-J plates and films and have been reduced to the systems defined by the northern data previously published by G. O. Abell. A revised northern catalog, including Bautz-Morgan types and redshifts where known, is also included. Subject headings: galaxies: clustering — galaxies: redshifts — galaxies: structure

Population studies in groups and clusters of galaxies. II - A catalog of galaxies in the central 3.5 deg of the Fornax Cluster

Abstract: A catalog of 2678 galaxies within an area of about 40 sq deg centered on the Fornax Cluster has been compiled based on 26 deep large-scale plates obtained with the 2.5-m Las Campanas Observatory reflector. The catalog includes 340 likely cluster members and 2338 likely background galaxies. Radial velocities are given for 89 of the galaxies. The spatial distributions of various types of galaxies have been modeled as the sum of a King (1962) model cluster component superimposed on a uniform background. Using maximum-likelihood fits to these distributions, a core radius of 0.7 deg is found for a King model fit to the cluster, suggesting that there are few cluster members contained in the sample of background galaxies.

Close pairs of galaxies in deep sky surveys

Abstract: A largely complete sample of 20 close pairs of faint galaxies, separated by less than 4.5 arcsec, is studied. The colors of the galaxy pairs indicate recently enhanced star formation in some systems, but generally the distribution of the colors and size of the galaxies in pairs is not significantly different from that of equally faint field galaxies. There is some evidence for an overabundance of pairs of galaxies separated by about 3.0 arcsec. A comparison of the number of close galaxy pairs in the faint sample to the number found in comparable nearby studies suggests that the frequency of interacting galaxies increases as (1 + z) exp 4.0 + or - 2.5. This result lends observational support to the hypothesis that interactions were more common in the past than they are now. 41 references.

Multicolor surface photometry of powerful radio galaxies. II. Morphology and stellar content

Abstract: Results on the morphology, photometric structure, and colors of 72 powerful radio galaxies (PRGs) are presented. It is found that galaxy interactions and mergers play an important role in the PRG phenomenon. Over 50 percent of the sample galaxies display optical morphological deviations from elliptical symmetry at high levels of surface brightness. About 20 percent of the galaxies have a second nucleus less than 10 kpc in projection from the main nucleus. The fraction of PRGs in a common envelope with neighboring galaxies is even larger. Surface brightness profiles for galaxies with weak or no emission lines are typically shallower in slope than normal radio-quiet elliptical galaxies, but similar to the brightest cluster galaxies. Surface brightness profiles for strong emission (SE) galaxies are more diverse in form. The SE PRGs have unusually blue average colors relative to giant elliptical galaxies. These colors are spatially extended and not merely due to light from a bright nucleus or extended emission-line gas.

Imaging and spectrophotometry of Virgo cluster irregular galaxies

Abstract: Large-aperture spectrophotometric observations and CCD images in the H-alpha and R bands have been obtained for Virgo cluster Magellanic, dwarf, and amorphous irregular galaxies. Although a small number of Virgo cluster irregulars have optical and H I properties consistent with recent gas loss, the rate of production of gas-poor irregulars is too low to account for the large population of Virgo cluster dE galaxies or to explain the deficiency in the number of irregulars relative to spirals. Radial brightness profiles reveal that only NGC 4641 follows the r exp 1/4 law of classical ellipticals, that four of the galaxies have exponential brightness distributions, and that one system has an indeterminant profile form. It is shown that the properties of Virgo cluster irregular galaxies can be best understood in terms of environmental modifications of normal systems in the circumcluster environment and in the cluster core. 78 refs.

A combined optical/X-ray study of the Galaxy cluster Abell 2256

Abstract: The dynamics of Abell 2256 is investigated by combining X-ray observations of the intracluster gas with optical observations of the galaxy distribution and kinematics. Magnitudes and positions are presented for 172 galaxies and new redshifts for 75. Abell 2256 is similar to the Coma Cluster in its X-ray luminosity, mass, and galaxy density. Both the X-ray surface brightness and the galaxy surface density distributions exhibit an elliptical morphology. The radial galaxy distribution is steeper than the density profile of the X-ray-emitting gas, yet the galaxy velocity dispersion is higher than the equivalent value for the gas. Under the simplest assumptions that the galaxy velocity distribution is isotropic and the gas is isothermal, the galaxies and gas cannot be in hydrostatic equilibrium in a common gravitational potential. Models consistent with available data have mass-to-light ratios which increase with radius and galaxy orbits that are anisotropic with a radial bias.

On the Kinematical Behavior of Galaxies in Clusters

Abstract: The sample of 15 galaxy clusters published by Dressler and Shectman (1988) has been analyzed to search for a tendency for spiral and irregular galaxies to have greater velocity dispersion than the ellipticals and lenticulars. It is shown that this trend is highly significant, with a probability of less than 0.05 percent that it may result from statistical fluctuations in the sample of clusters. An analogous but much less significant effect appears also to be present between lenticular and elliptical galaxies. These results are interpreted as evidence that late-type galaxies are still in the process of infalling toward the virialized cluster cores. 34 refs.

Stellar Content of Nearby Galaxies. II. The Local Group Dwarf Elliptical Galaxy M32

Abstract: Using the CCD camera on the Canada-France-Hawaii Telescope, color-magnitude (C-M) diagrams were obtained for brightest stars of the Local Group dwarf elliptical galaxy M32. Both the I vs (V-I) and I vs (R-I) CCD C-M diagrams reveal a red population of stars, the brightest of which resolve at I of about 19.5 mag. Data on the (V-I) and (R-I) colors indicate that the mean metallicity of M32 is greater than that of the most metal-rich Galactic globular clusters. A discontinuity in the I band luminosity function of the M32 was observed, which, if the distance modulus of M32 is comparable to that of M31, is consistent with the appearance of the tip of the first red giant branch in this galaxy. 37 refs.

Observations of deep 2 micron survey galaxies: primeval galaxy candidates

Abstract: Des observations spectroscopiques et photometriques BVRIJHK de 2 galaxies rouges ont ete effectuees et leur appartenance a une nouvelle population extragalactique, probablement des galaxies primordiales, a ete suggeree (Elston R., Rieke G. H. et Rieke M. J., 1988, Ap. J. Letters, 331). De nouvelles observations de ces 2 galaxies sont presentees

Gravitationally lensed images in Abell 370

Abstract: Several blue arclike images have been found in the galaxy cluster A370, some up to 1 arcmin from the cluster center. It is shown here that gravitational lensing can account for the positions and lengths of the observed arcs without having to resort to any extreme or peculiar cluster mass distribution, provided there is a significant amount of dark matter in the cluster. The constraints that can be placed on the core radius and ellipticity of the cluster and on the redshifts of the background galaxies are discussed. 32 refs.

Infrared Emission from Compact Groups of Galaxies

Abstract: A search of the IRAS Point Source Catalog, Version 2 has revealed infrared sources within 1 arcmin of the optical centers of 54 galaxies in Hickson's catalog of compact groups of galaxies. The 60-micron luminosity function for these galaxies has the same shape as the luminosity function of the IRAS bright galaxy sample. The space density of IRAS galaxies in compact groups is 60 times smaller than the space density of IRAS bright galaxies, indicating that of order 1 percent of all bright IRAS galaxies are in compact groups. The infrared emission from these galaxies is compared with the emission from samples of isolated galaxies by Keel et al. (1985) and cluster galaxies studied by Bicay and Giovanelli (1987). The fractional distribution of the ratio of far-infrared to optical luminosity of compact group galaxies is significantly larger than that of the isolated galaxies and comparable to that of the cluster galaxies. These results indicate that infrared emission is enhanced in the compact group galaxies, probably because of interactions. 24 refs.

Galaxy Populations in the Fornax and Virgo Clusters

Abstract: In these first results from a photographic survey of nearby clusters and groups of galaxies, we compare the luminosity functions of galaxies of various Hubble types in the core of the Formax cluster to luminosity functions in the core of the Virgo cluster from Sandageet al. (1985). The galaxy classifications for the two clusters are based on identical plate material, and are hence directly comparable. The properties (galaxy density, velocity dispersion, X-ray luminosity) of the two clusters are quite different, yet we find few significant differences in the luminosity functions, or in the morphological mix of galaxies between the two clusters. In particular, while there is some indication that the ratios of giants to dwarfs and early to late-type galaxies in the two clusters differ, we cannot exclude the possibility that the ratios are identical. We discuss the selection limits of our survey and the completeness corrections that must be applied to the faint end of the luminosity function. The effective surface brightness of early-type galaxies in our sample decreases with decreasing luminosity. We show that this correlation is not an artifact of our selection criteria for dwarf spheroidal galaxies and use it to determine the relative distances to the Fornax and Virgo clusters. We also present evidence for a radial variation in the luminosity function of dwarf ellipticals within the two clusters in the sense that the faint end of the luminosity distribution is enhanced at the centre of each cluster.

The unusual radio galaxy 3C 288

Abstract: VLA observations of the radio galaxy 3C 288 at 1.5, 4.9, and 15 GHz are presented. The features revealed in the data include a jet and counterjet near the radio core and faint wings of emission connected to the elongated lobes. The results suggest that the host galaxy is probably the dominant member of a distant cluster. It is found that the larger-scale structure of 3C 288 may be an example of a disturbed secondary-flow pattern. 58 references.

Surface Brightness Fluctuations and the Distance to the Virgo Cluster

Abstract: Preliminary results from a project to measure the fluxes of giant stars in M32, NGC 3379, and five Virgo Cluster galaxies are presented. Since the Virgo Cluster galaxies are approximately equidistant, variations in observed fluctuation amplitude from galaxy to galaxy can be ascribed to variations in absolute luminosity of the giant stars in the galaxies. Assuming a distance of 0.72 Mpc for M32 and correcting for the color effect in m-bar, the typical brightness of giant stars, distances of 9 Mpc for NGC 3379 and 14 Mpc for Virgo, accurate to about 10 percent, are derived. This is used to find a Hubble constant of 88 km/s/Mpc. The method can be used to measure m-bar in galaxies at least 40-50 Mpc distant.

The Structure of Host Galaxies of Radio-loud Quasars and Possible Triggering Mechanisms for Quasar Activity

Abstract: An image modeling program is used to analyze optical imaging data for a sample of radio-loud quasars with redshifts between 0.2 and 0.7. It is found that the host galaxies of these quasars tend to be more compact than normal ellipticals. The cooling flow cluster elliptical galaxies near these host galaxies are studied. It is suggested that these cooling flow galaxies are also compact due to star formation in their central regions. Two populations of quasars are identified. One, in which activity is triggered by galaxy mergers of interactions has predominately spiral galaxies and are radio quiet. The other, in which activity is triggered by star formation bursts induced by cooling flows, has predominately elliptical hosts and may be radio loud.

The distribution of cluster members in the vicinity of a central dominant galaxy

Abstract: The projected distribution of cluster members within 250/h kpc of a central dominant galaxy is determined based upon CCD images of 29 galactic clusters. It is found that the radial distribution of the projected galaxy number density is well described by an exponential profile with an e-folding length of about 100/h kpc. The dynamics of the projected profile are studied for a range of possible mass distributions, and existing redshift data are found to be consistent with an isotropic velocity distribution. It is suggested that the high central density associated with this cusped distribution may explain the presence of at least 50 percent of the observed multiple nuclei projected within 10/h kpc of the center of the dominant galaxy. It is noted that the high densities and low velocities of galaxies in the cluster core may lead to a sufficiently high rate of collisions between cluster members and the central dominant galaxy to produce a significant population of multiple nuclei which are in the process of merging with the underlying central galaxy. 42 refs.

First-ranked Cluster Galaxies: A Two-Population Model

Abstract: The small dispersion in the absolute magnitudes (about 0.35 mag) of first-ranked galaxies in rich clusters has been the cause for much debate between the special and statistical hypotheses for these galaxies. Here, statistical evidence is presented that it is not the one or the other, but a combination. The distribution in magnitudes of the brightest galaxies is best explained if they consist of two distinct populations of objects: (1) a population of special galaxies having a Gaussian distribution of magnitudes with a small dispersion (0.21 mag), and (2) a population of extremes of a statistical luminosity function. The best-fit model requires that 63 percent of the clusters have a special galaxy that is, on average, 0.48 mag brighter than the brightest normal galaxy. 16 references.

The Butcher-Oemler effect in a nearby cluster of galaxies

Abstract: The integrated spectra of early-type galaxies in the nearby Abell 262, Pegasus I, and Virgo clusters are compared with those of several field galaxies. The spectra of five galaxies in Pegasus I and one galaxy in the Virgo Cluster show evidence of recent star formation. The average blue magnitude for the star-forming galaxies is M(B) = -20. The star-formation activity in Pegasus I is found to be similar to that of starburst and poststarburst galaxies in Butcher-Oemler clusters at redshifts greater than 2. 38 refs.

Is cosmic drift a cosmic myth

Abstract: Systematic variations in the mass-to-light ratios of elliptical and spiral galaxies are examined. It is suggested that a major component of the apparent peculiar velocity field on large scales may be these variations over cluster scales. A dispersion in the mass-to-light ratio of elliptical galaxies is attributed to tidal stripping during cluster formation. The dispersion is strongest in cluster cores and is specific to galaxies that have undergone the bulk of their star formation prior to cluster formation. Evidence is presented to support this explanation of the variations.

Vacuum ultraviolet imagery of the Virgo cluster region

Abstract: The results are reported of an experiment using the UV imager aboard an attitude-controlled S520 type sounding rocket. The total UV fluxes of galaxies in the Virgo Cluster as well as the flux level of the diffuse UV background around the cluster were measured. The data on NGC 4486 and NGC 4472 confirm the variation in the degree of the 'turnup' below 200 nm in the energy spectrum of the total light of elliptical galaxies. At two-color diagram of galaxies of visual/near-UV/vacuum UV indicates that colors of spiral galaxies are distributed within a strip and well-correlated with the morphological type, while elliptical galaxies are located differently from spiral galaxies. 51 refs.

Constraints on the Epoch of Galaxy Formation from Deep U-Band Counts

Abstract: Two new galaxy count surveys in the ultraviolet probe the count-magnitude relation to U ≳ 25.5. The most straightforward interpretations of the results are consistent with mild evolution and zf > 4.5. To the depth of the surveys, no evidence is seen for the existence of a significant population of z > 3.5 galaxies.

Intrinsic shape of dwarf elliptical galaxies

Abstract: The intrinsic shape of the dwarf elliptical galaxies is examined. Two methods are applied to the sample of 98 dwarf elliptical galaxies in the Virgo Cluster. One is to estimate the intrinsic flattening distribution from the apparent-flattening distribution; the other is to estimate the spatial shape from the relation between the apparent flattening and surface brightness. The result of both methods are consistent with the intrinsic shape of dwarf elliptical galaxies being the oblate spheroid with a mean axial ratio of 0.6, if there is no relation between intrinsic shape and intrinsic surface brightness. It seems that dwarf elliptical galaxies have shapes similar to normal elliptical galaxies. The absence of the correlation between the apparent axial ratio and the luminosity in both normal and dwarf elliptical galaxies suggests that all the elliptical galaxies have similar shapes. 34 refs.

Further spectroscopic studies of the Bootes region - Two more galaxies in the void

Abstract: Redshifts are reported for 40 galaxies in the direction of the Bootes void identified in the Case Low-Dispersion Northern Sky Survey, List IV. Two new emission-line galaxies have been discovered in the void. The density of bright emission-line galaxies in the void is estimated to be a factor of 3 + or - 2 lower than the density of similar galaxies in the field. The galaxies are distributed uniformly with distance from the void center. A previously reported correlation between Case IV redshift estimates and measured redshifts is confirmed. Data for previously observed IRAS galaxies are combined with the present results to compared the luminosity distribution of IRAS galaxies to that for emission-line galaxies. The IRAS luminosity distribution contains a greater fraction of intrinsically bright galaxies than the emission-line galaxy distribution.

Galaxy Evolution in High Density Environments

Abstract: There exists by now almost unequivocal evidence that there has been strong evolution of the population of galaxies in clusters over the relatively short span of the last third of the age of the universe (z ≈ 0.5), and what data there is suggests strongly that even much more marked effects occur between then and z = 1. We discuss the mechanism for this strong evolution, and argue that large galaxies were very much more gas-rich even a relatively short time ago than now. There is hope that some galaxies in clusters have evolved sufficiently “passively” that their formation can be dated, but the relevance of the derived ages to the epoch of galaxy formation in general is clouded by statistical considerations.

Clusters of Galaxies Associated with Quasars. I. 3C 206

Abstract: Multislit spectroscopy and three-color CCD photometry of the galaxies in the cluster associated with the quasar 3C 206 (PKS 0837-12) at z = 0.198 are presented. This cluster is the richest environment of any low-redshift quasar observed in an Abell richness class 1 cluster. The cluster has a very flattened structure and a very concentrated core about the quasar. Most of the galaxies in this field have colors and luminosities consistent with normal galaxies at this redshift. The background-corrected blue fraction of galaxies is consistent with values for other rich clusters. The existence of several blue galaxies in the concentrated cluster core is an anomaly for a region of such high galaxy density, however, suggesting the absence of a substantial intracluster medium. This claim is supported by the Fanaroff-Riley (1974) class II morphology of the radio source. The velocity dispersion calculated from 11 spectroscopically confirmed cluster members is 500 + or - 110 km/s, which is slightly lower than the average for Abell class 1 clusters. A high frequency of interaction between the quasar host galaxy and cluster core members at low relative velocities, and a low intracluster gas pressure, may comprise a favorable environment for quasar activity. The propertiesmore » of the cluster of galaxies associated with 3C 206 are consistent with this model. 59 refs.« less

The binary-rich cluster Abell 2244

Abstract: A structural, luminosity, and velocity study of the cluster Abell 2244 is presented. A2244 was selected for study from the list of Struble and Rood because of its unusually binary-rich population in an evolved cD-type cluster environment, a contradiction in terms of cluster collapse scenarios versus the formation and survival of bound pairs. In comparison with the Coma cluster, A2244 is a slightly poorer version with a suspected deficiency in the number of cluster members in the core. This evidence, combined with the high-velocity dispersion of the cluster, suggests that a low-velocity population of galaxies has been consumed by the central cD galaxy. The central cD galaxy has a single low-velocity companion deep in its envelope and cross sections of its surface-brightness profile suggest that it is in transition from a depressed central surface-brightness object to a high central concentration system, a point of contention in merger models. All but two of the binary galaxies were found to be projections with other cluster members or stars and, thus, are not in conflict with the advanced dynamical age of the cluster. 35 refs.

Alignments and Filaments on Large Scales

Abstract: By means of statistical analyses on the Lick maps, the reported alignment effects of brightest cluster galaxies and ellipticals with the neighboring galaxy distribution, are confirmed. No peculiarities in the distribution around spirals and S0 were found, suggesting a lack of correlation of angular momentum with the neighboring galaxy distribution. It is found that the alignment signals are consistent with the presence of filaments or sheets of galaxies running across clusters and ellipticals rather than with a single overdensity on one side of these structures. 19 refs.

The large-scale distribution of galaxies

Abstract: Six strips of the CfA redshift survey extension are now complete. The data continue to support a picture in which galaxies are on thin sheets which nearly surround vast low density voids. In this and similar surveys the largest structures are comparable with the extent of the survey. Voids like the one in Bootes are a common feature of the large-scale distribution of galaxies. The observed structure presents a serious challenge for models.