Showing papers on "Brightest cluster galaxy published in 1986"

Globular clusters in galaxies beyond the local group. V. The giant ellipticals reconsidered.

Abstract: The large-scale spatial structures of the globular cluster halo systems around the giant ellipticals M87 and M49 in Virgo, and NGC 3311 in Hydra I, are analyzed following a revision of the previously published star counts around these galaxies. Comparison of these three systems, and comparison with several other halo systems in galaxies of different sizes and types, has led to several new results connected with the structures of globular cluster systems in general: (a) The globular cluster systems in M87 and M49 have spatially identical structures within observational uncertainties. Both have projected logarithmic slopes ..cap alpha.. = ..delta.. log sigma/..delta.. log rapprox. =-1.7 over almost the entire range of their halos. The only obvious difference between them is their total cluster population (specific frequency Sapprox. =15 for M87, Sapprox. =6 for M49). (b) Both the M87 and M49 cluster systems are spatially less centrally concentrated than the underlying halo light of the galaxies, by ..delta cap alpha..approx.0.7. This fundamental structural difference between subsystems of the halo is considerably more well established than in previous discussions, and applies to every measurable part of their halos from near the center out to rapprox.100 kpc. (c) The NGC 3311 cluster system ismore » even ''flatter'' (..cap alpha..approx. =-1.3) than the ones in the Virgo« less

Molecules in Galaxies. III. The Virgo Cluster

Abstract: Using the 7 m Bell Laboratories antenna, observations of 47 spiral galaxies in the Virgo Cluster were made in the (C-12)O J = 1-0 line; CO emission from 25 of the galaxies was detected at greater than the 3 sigma level. Most of the galaxies were observed at the central position, as well as at four adjacent positions one beam-width away. A method is presented for estimating the total flux of the galaxy using this spatially undersampled map. The total CO emission is found to be correlated with radio continuum emission and 60 + 100 micron band far-infrared, reflecting direct relationships among molecular gas content, CO emission, and massive star formation in these galaxies. However, the total CO flux is only poorly correlated with visual blue luminosity. 49 references.

Redshift asymmetries in systems of galaxies and the missing mass

Abstract: Redshift asymmetries were used to study contamination by optical companions in binary galaxy samples, with Karachentsev's sample found to be relatively free of these contaminants. Redshift asymmetries were also used to study the dynamical state of groups and clusters of galaxies, revealing that groups are composed of an expanding population. With regard to clusters, a massive central binary dominates the Coma Cluster, making it dynamically unstable, noting that other rich clusters have similar massive cores and are largely unbound. Coma Cluster models with much missing mass were found to be improbable. This missing mass problem exmined in detail, with attention focussed on Karachentsev's binary galaxies, rotation curves of spiral galaxies, dwarf companions of the Milky Way Galaxy, the dynamically unstable state of galaxy groups and clusters, and the cosmic virial theorem. The cosmological density parameter was estimated at 0.02, concluding that galaxies, and clusters of galaxies are not missing mass in large enough amounts to close the universe. 118 references

Faint galaxies and cosmology.

Abstract: This paper reviews progress in two areas of optical research on faint galaxies. First the author discusses the philosophy and techniques needed to employ radio galaxies as evolutionary and cosmological probes out to redshifts now approaching 2.0. The distant radio galaxies seem to be systematically more active than their nearby counterparts. Radio galaxies can also be studied as galaxies of evolving stars; the present interpretations of visual and IR galaxy colors and magnitudes suggest modest lingering star formation over the past 1010years in many luminous radio galaxies. The author concludes with a discussion on the location and utilization of faint radio-quiet red galaxies; these are giant E systems at z ≥ 0.5.

Radio continuum survey of the Coma/A1367 supercluster. III. Properties of galaxies in different density environments

Abstract: The analysis of a radio continuum survey of 724 galaxies in the Coma Supercluster region is reported. The analysis is based on the radio luminosity function (RLF) and on the distribution of the radio to optical ratio function of galaxies in different regimes of local galaxy density and of different morphological types. For low and moderate luminosities, the RLFs of E/SO galaxies in clusters, groups, and multiple systems are found to be similar. Isolated galaxies are radio-poor by a factor of about five. Spirals in rich clusters have a typical luminosity about 10 times higher than galaxies outside clusters. The radio-bright cluster spirals are mostly late morphological types. High radio luminosity in cluster spirals correlates well with indicators of star formation and with H I deficiency. This suggests that interaction with the cluster medium leads to collapse of molecular clouds, star formation, generation of cosmic rays, and morphological distortions. 46 references.

Hierarchical structure in the distribution of galaxies

Abstract: The distribution of galaxies has a hierarchical structure with power-law correlations. This is usually thought to arise from gravity alone acting on an originally uniform distributioon. If, however, the original process of galaxy formation occurs through the stimulated birth of one galaxy due to a nearby recently formed galaxy, and if this process occurs near its percolation threshold, then a hierarchical structure with power-law correlations arises at the time of galaxy formation. If subsequent gravitational evolution within an expanding cosmology is such as to retain power-law correlations, the initial r exp -1 dropoff can steepen to the observed r exp -1.8. The distribution of galaxies obtained by this process produces clustering and voids, as observed. 23 references.

Elliptical galaxies and non-uniformities in the hubble flow'

Abstract: We have obtained spectroscopic and photometric data for 400 elliptical galaxies that permit us to predict distances to individual galaxies with accuracies of ±23%. Systematic velocities relative to a smooth Hubble flow are observed that are most straightforwardly interpreted as a bulk motion of approximately 700 km/s towards l=299°, b=+1° for galaxies within 60 h-1 Mpc of the Local Group, A preliminary estimate for the rms motion of elliptical galaxy gruops relative to the bulk motion is 300 km/s. Spiral galaxies studied by Aaronson et al. and by Rubin et al. yield similar results for both the bulk and the rms motion.

Wide-angle tailed radio galaxies.

Abstract: In this paper, the properties of a class of extragalactic radio sources associated with dominant cluster galaxies known as wide-angle tails (WATs) are reviewed. The mechanism responsible for forming and, in particular, bending these sources remains controversial nearly 10 years after their discovery. To gain possibly new insight into these radio galaxies, we divide them into three subclasses according to linear size. The smallest WATs are limited in size to the optical extent of the galaxies, are weaker in radio power, and may be bent by dynamic pressure as a result of motion of the radio galaxy about a second large galaxy or subcondensation of galaxies in the cluster. The large, 1-Mpc size WATs are associated with a single, dominant cD galaxy, have only sharp and irregularly placed bends in the jets, and probably interact with clouds in the cluster gas. The moderate-size, symmetrically bent WATs such as 3C 465 may bend and decollimate as a result of the passage of a jet through a sharp pressure gradient,...

Direct imaging of the extremely large host galaxy and gas cloud surrounding the quasar 3C275.1

Abstract: Direct CCD images of the field of the quasar 3C275.1 have been obtained using v, r, and redshifted forbidden O II filters to study the ionized gas cloud surrounding the quasar and to determine the gross characteristics of the quasar host galaxy. The images show an elliptical substrate containing several bright knots and indicate that the host galaxy is extremely large and luminous. The host galaxy's luminosity, dimensions, and position at the cluster center suggest that it may be a cD or 'proto-cD'. The nebulosity may be accreting matter from a 'cooling flow' of the intracluster medium. Alternatively, the quasar and the surrounding galaxy and gas cloud may be the result of repeated galaxy collisions.

Quests for Primeval Galaxies: A Review of Optical Surveys

Abstract: Optical surveys explicitly designed to detect continuum or line emission from individual primeval galaxies are reviewed. In addition to such searches, a variety of recent redshift surveys of very faint quasars, radio sources, and galaxies are also useful in constraining the epoch, number, and brightness of galaxies during their birth. The serendipity discoveries of a few high-redshift objects with narrow emission lines are tantalizing. Presently the strongest constraints come from long-slit spectroscopy of blank sky to search for Lyman a emission. The lack of positive detections suggests that galaxy formation occurred at redshifts z > 5, a result consistent with the lack of primeval galaxies among samples of quasars fainter than B = 20 and with the mild evolution predicted by models that fit faint galaxy counts and colors.

Narrow-band photometry and the evolution of galaxies.

Abstract: A new approach to the use of narrow-band filters in extragalactic research is described. The photometric system vz, bz, yz essentially imitates, at the redshift of the cluster of galaxies in question, the Stromgren v, b, y passbands. This system has some obvious advantages: the uncertainties associated with k-corretions are bypassed, and the passbands avoid the stronger emission lines appearing in the spectra of some normal and most active galaxies. It is necessary to acquire filters for each redshift value and to have accurate spectrophotometry for at least one galaxy at the redshift in order to calibrate the photometry. It is shown that the vz, bz, yz filter system is especially suitable for testing the evolutionary synthesis models. For that purpose 48 CCD frames of three clusters of galaxies (Abell 665, the small cluster around 3C 234, and Cl 1021.1+0427) were obtained. For galaxies, metric magnitudes were derived corresponding to a linear physical standard diameter of 32 kpc (H0 = 60 km s-1Mpc-1, q0 = 0.5). Galaxies showing a strong color gradient along their images (disk galaxies) are distinguished from galaxies with no, or very small, color gradient along their images (elliptical and lenticulars).

Three-color CCD photometry of the distant cluster of galaxies Cl 0024 + 1654

Abstract: Photometry of 265 galaxies in rich cluster Cl 0024 + 1654 (z = 039), based on CCD imaging in three filters, is presented The luminosity of this system ranks it among the richest known clusters, and it has a blue mass-to-light ratio of about 210 The color-magnitude diagram has a prominent E/S0 sequence There are essentially no blue cluster members brighter than r equals about 193, and only very red galaxies inhabit the central 30 arcsec of the cluster The blue cluster members have sizes and surface brightnesses similar to spiral galaxies in nearby clusters

An Improved Distance Indicator for Elliptical Galaxies

Abstract: We present a new relation between velocity dispersion, surface brightness, and radius (or luminosity) for elliptical galaxies. Relative distances of galaxies can be estimated to within 0.13 in log D. Most or all of that uncertainity is due to the measurement errors, and it may be reduced further. Our analysis shows that the elliptical galaxies are at least a three-parameter family. We discuss briefly the implications for theories of galaxy formation.

Quasars in the central region of the Virgo Cluster

Abstract: Quasars found from objective prism searches have been reported to show no association with galaxies in the Virgo Cluster. A simple analysis here shows significant association of the brightest of these quasars with core galaxies in the Virgo Cluster.

HI Properties of Spiral Galaxies in the Virgo Cluster

Abstract: The main aim of this invesigation was to contribute to an understanding of the evolution of galaxies in a cluster environment, through a study of the effects of such an environment on the neutral-hydrogen properties of galaxies. For this purpose HI observations have been carried out with the Westerbork Synthesis Radio Telescope (WSRT) to determine the radial distributions of the HI surface density for a sample of 36 spiral galaxies in the Virgo Cluster. These HI distibutions have been compared with those in sample of galaxies in a low-density environment (field sample). ... Zie: SUMMARY AND SUGGESTIONS FOR FUTURE WORK

Kinematic evidence of satellite galaxy populations in the potential wells of first-ranked cluster galaxies

Abstract: The velocities of 38 centrally positioned galaxies (r much less than 100 kpc) were measured relative to the velocity of the first-ranked galaxy in 14 rich clusters. Analysis of the velocity distribution function of this sample and of previous data shows that the population cannot be fit by a single Gaussian. An adequate fit is obtained if 60 percent of the objects lie in a Gaussian with sigma = 250 km/s and the remainder in a population with sigma = 1400 km/s. All previous data sets are individually consistent with this conclusion. This suggests that there is a bound population of galaxies in the potential well of the central galaxy in addition to the normal population of the cluster core. This is taken as supporting evidence for the galactic cannibalism model of cD galaxy formation.

Galaxy Distribution in Butcher-Oemler Clusters

Abstract: The galaxy distribution in six Butcher-Oemler clusters is analyzed in order to obtain separate core radii for the blue galaxies and for the red E-sequence galaxies. By fitting these distributions with isothermal spheres via maximum-likelihood techniques, the core radius for the blue galaxies is shown to be nearly three times that of the red galaxies. While the general trend of the blue/red galaxy segregation was noticed by Butcher and Oemler, the analysis is presented here places this result on firm statistical ground. A test for luminosity segregation gives only marginally significant results, while a comparison of differential luminosity functions shows that blue galaxies, in their quiescent state, are likely to be about 1 mag fainter than red E-sequence galaxies. When combined with each other, the two previous results imply that mass segregation cannot explain the broad blue galaxy distribution. A discussion of dynamical considerations particularly the relative velocity dispersions of blue and red galaxies - is included to show how the blue/red galaxy segregation might arise. 17 references.

The galaxy luminosity function and the redshift-distance controversy (A Review).

Abstract: The mean relation between distance and redshift for galaxies is reviewed as an observational question. The luminosity function for galaxies is an important ingredient and is given explicitly. We discuss various observational selection effects that are important for comparison of the linear and quadratic distance-redshift laws. Several lines of evidence are reviewed, including the distribution of galaxy luminosities in various redshift ranges, the luminosities of brightest galaxies in groups and clusters at various redshifts, and the Tully-Fisher correlation between neutral hydrogen velocity widths and luminosity. All of these strongly favor the linear law over the quadratic.

Galaxies in the Infrared

Abstract: In this paper we review IRAS studies of galaxies and we attempt to systematically present the new insights that have resulted from these studies.

Constraints on the Ages of Distant Giant Elliptical Radio Galaxies

Abstract: The oldest observed ages of elliptical galaxies and globular clusters form a logical lower limit to the age of the Universe. To find the earliest possible formation epoch of elliptical galaxies one needs to study candidates at high redshift, which have very red colors and whose spectra consist entirely of starlight. To derive ages from observed spectra or colors one must first understand the stellar populations that compose the gE spectrum, their evolutionary tracks in the HR diagram and the resulting spectral evolution of the entire stellar population with cosmic time.

Flyby - Numerical experiments on a galaxy orbiting within a galaxy cluster

Abstract: Dynamical effects on a self-consistent stellar system in orbit around an attracting force center have been studied by means of numerical experiments. Globular clusters in the Galaxy, galaxies within a cluster, and dwarf spheroidal galaxies in orbit around our Galaxy are examples of this dynamical problem. Stars within the galaxy move in the combined self-consistent and external (cluster) force fields, in an accelerated frame, and the galaxy orbit is integrated at the same time. The principal result found is that, in practice, a spherical galaxy either suffers little mass loss (less than 1 percent) or is totally disrupted. A disruption criterion based on the ratio of tidal stress to internal stress within the galaxy describes the results succinctly. This criterion is used to discuss the distribution of dark mass in galaxy clusters. A galaxy envelope expands, rather than being tidally truncated, following a flyby. Spiral galaxies can show tidal damage after flying past the cluster center, even without a close encounter with another galaxy.