Showing papers on "Brightest cluster galaxy published in 1988"

Extended optical-line-emitting gas in radio galaxies: broad-band optical, narrow-band optical, and radio imaging of a representative sample

Abstract: A search for extended optical-line-emitting gas in a representative sample of power radio galaxies has been conducted in order to determine the frequency with which such gas is found in these galaxies and to assess the relationship of the gas to the radio source structure and the structure of the host galaxy. Contour maps and detailed descriptions are given for each source of the broad-band optical, narrow-band optical, and radio images obtained. From the images presented here, it is clear that extended optical-line-emitting is common in powerful radio galaxies. In some cases, the emission-line filaments appear to connect the host radio galaxy to an apparent companion galaxy. S-shaped regions of line emission are observed in five of the sources. Morphological peculiarities in the distribution of the optical continuum light from the host radio galaxy are also apparent in many of these sources. 109 references.

Evidence for Galaxy-Galaxy Interactions as an Active Agent of the ``Butcher-Oemler Effect'' at a Redshift of 0.2

Abstract: The spectra and images of 10 blue emission-line galaxies observed in Abell 963 (5), Abell 2111 (4), and Abell 2125 (1) are presented. A wide range in the spectral properties of the galaxies is found, yet the large majority of the galaxies has spectra which are consistent with very recent star formation. Only one of the 10 galaxies appears to contain an active nucleus. Since star formation is now occurring in these galaxies, residual effects from the triggering mechanism may still be apparent. Images of these emission-line galaxies show that several appear to be members of interacting systems. Others show evidence for possible interactions, either being somewhat morphologically disturbed or having disturbed neighbor galaxies. To test the idea of interactions, a nearest neighbor analysis on these emission-line galaxies and a sample of red galaxies was performed using the Kolmogorov-Smirnov test. The emission-line galaxies have closer neighbor galaxies than the red galaxy sample at greater than the 98 percent level of confidence. From this result and from the images themselves, it is concluded that galaxy-galaxy interactions can induce bursts of star formation and are an active agent of the Butcher-Oemler effect at redshifts near 0.2. These interactions may be the primarymore » cause of the B-O effect. 40 references.« less

Population studies in groups and clusters of galaxies. I - The luminosity function of galaxies in the Fornax Cluster

Abstract: The luminosity functions of galaxies of various Hubble types in the central 2.4-deg-radius core of the Fornax Cluster and the 6-deg-radius core of the Virgo Cluster have been compared. Although properties such as density, velocity dispersion, and X-ray luminosity differ in the two clusters, no significant differences are noted in their luminosity functions or in their morphological mix of galaxies. The ratio of the distances to the Fornax and Virgo clusters has been obtained. Evidence is provided for a radial variation in the luminosity function of dwarf ellipticals in the two clusters.

Low surface brightness galaxies in the Fornax Cluster - Automated galaxy surface photometry. III

Abstract: A sample of low surface brightness galaxies in the Fornax Cluster region which has been measured by the automated plate measuring machine is presented. Photometric parameters, namely profile shape, scale length, central brightness and total magnitude, are derived for the sample galaxies, and correlations between the parameters of low surface brightness dwarf galaxies are discussed, with particular reference to the selection limits. Contrary to previous authors, no evidence is found for a luminosity-surface brightness correlation in the sense of lower surface brightness galaxies having lower luminosities and scale sizes. In fact, the present data suggest that it is the galaxies with the largest scale lengths which are more likely to be of very low surface brightness. In addition, the larger scale length galaxies occur preferentially towards the center of the Cluster.

Properties of H II Region Populations in Galaxies. I. The First-ranked H II Regions

Abstract: H-alpha photometry of the brightest H II regions in 95 nearby spiral and irregular galaxies has been analyzed in order to study the dependence of the H II region populations on the properties of their parent galaxies. It is found that the brightest H II regions in Magellanic irregular galaxies are about 50 times brighter than those in early-type spirals of the same absolute magnitude. It is suggested that this difference is due to both an increase in the numbers of H II regions in late-type galaxies and a physical change in the characteristic sizes of the star-forming regions. 62 references.

Morphology of galaxies in compact groups

Abstract: Results of a study of galaxy morphology in a homogeneous sample of 98 compact groups of galaxies are reported. Of all the galaxies, 49 percent are of late morphological type (S + Irr), somewhat less than the corresponding fraction for field galaxies. Similarly, for first-ranked galaxies only, 48 percent are late type. Several strong correlations are found between galaxy type and the galaxy environment. Morphological concordance occurs between galaxies within a group. Galaxy morphological type correlates with group optical luminosity, and galaxy morphology correlates with velocity dispersion. The latter correlation is found to be the more fundamental of the two. No strong correlation between morphological type and galaxy space density is found in these compact groups, contrary to the situation in rich clusters and loose groups. These results indicate that the morphological types of galaxies in compact groups are strongly influenced by the environment, and that this influence occurs mostly at the time of galaxy formation.

The morphology of multiple-nucleus brightest cluster galaxies

Abstract: The morphology of high SNR CCD images of 16 multiple-nucleus brightest cluster galaxies is studied using an algorithm that models images of the systems as the line-of-sight superposition of normal elliptical galaxies. The algorithm is applied initially to the classic multiple-nucleus cD galaxy in A2199. Evidence is found suggestive of deep interpenetrating high-speed encounters by its secondaries. The interactions effects studied include noncentric isophotes, brightness profile effects, excess light around primary galaxies, and dynamical friction wakes. The results show that in many cases multiple systems are interacting systems.

The Enhancement of Infrared Emission in Interacting Galaxies

Abstract: Selected infrared properties, based on IRAS observations, of two categories of interacting galaxy pairs from the Arp-Madore Catalogue of Southern Peculiar Galaxies and Associations are examined. For pairs of comparably sized galaxies, a strong tendency exists for pairs with the highest far-IR color temperatures to have the smallest separation. This finding implies that galaxy interactions significantly enhance the intensity or the efficiency of star formation. No trend of far-IR color temperature varying with pair separation is found for pairs consisting of a galaxy with a small companion. There are 10 times as many pairs in the sample that contain one IRAS far-IR galaxy as there are pairs for which both galaxies were detected by IRAS, thus strengthening previous conclusions that the effect of a perturbation depends strongly on the detailed geometry of the interaction.

Alignments of Brightest Cluster Galaxies with Large-Scale Structures

Abstract: Using an independent sample of brightest galaxies in rich clusters in the southern galactic hemisphere, the Argyres et al. (1986) result that galaxy counts on scales to at least 15/h Mpc are systematically higher in the direction of the major axes of brightest cluster galaxies is confirmed.

Atlas of Galaxies Useful for Measuring the Cosmological Distance Scale

Abstract: A critical first step in determining distances to galaxies is to measure some property of primary objects such as stars of specific types, H II regions, and supernovae remnants that are resolved out of the general galactic star content With the completion of the Mount Wilson/Palomar/Las Campanas survey of bright galaxies in 1985, excellent large-scale photographs of the complete Shapley-Ames sample were on hand Most of the galaxies useful for distance scale calibration are in this collection This atlas contains photographs of 322 galaxies including the majority of all Shapley-Ames bright galaxies, plus cluster members in the Virgo Cluster core that might be usefully resolved by the Hubble Space Telescope (HST) Because of crowding and high background-disk surface brightness, the choice of field position is crucial for programs involving resolution of particular galaxies into stars The purpose of this atlas is to facilitate this choice Enough information is given herein (coordinates of the galaxy centers and the scale of the photography) to allow optimum placement of the HST wide-field planetary camera format of approximately 150 arc-seconds on a side

Kinematics and ionization of extended gas in active galaxies. VI - The Seyfert 2 galaxy NGC 1386

Abstract: The results of direct CCD imaging and long-slit medium-dispersion spectroscopy of the extended narrow-line-emitting gas in the nearby Seyfert 2 galaxy NGC 4388 are presented. The spectra are used to investigate the distribution, kinematics, and ionization structure of the excited gas in the regions surrounding the nucleus out to a distance of about 4.8 kpc. The data support earlier suggestions that the galaxy, which appears to lie near the core of the Virgo cluster, has been tidally distorted, possibly by the nearby cluster core galaxies M84 or IC 3303. Much of the highly ionized gas in the galaxy appears to be distributed in two wide cones originating from the nucleus and extending above and below the disk. Explanations are offered for the distribution of this gas and for the remainder of the gas above and below the disk.

Rotation curves for spiral galaxies in clusters. II. Variations as a function of cluster position

Abstract: Inner and outer velocity gradients, residuals from synthetic rotation curves for field spirals, and M/L gradients are used to study the rotation curves of spiral galaxies. A good correlation is found between the outer gradient of the rotation curve and the galaxy's distance from the cluster center, with a similar effect noted in the residuals between the observed and synthetic rotation curves. A correlation is also shown to exist between the M/L gradient across a galaxy and the galaxy's position in the cluster. The results suggest that the inner cluster environment may strip away some fraction of the mass in the outer halo of a spiral galaxy or may not allow the halo to form. 27 references.

Dynamics of the Hydra I galaxy cluster

Abstract: This paper examines the dynamics of the Hydra I cluster. This cluster has circularly symmetric galaxy and X-ray distributions, and a velocity histogram that is close to Gaussian. However, the velocity distribution of galaxies near the cluster center is very flat. Using various statistical tests, the probability that the observed velocities were drawn from a normal distribution, or from a set of spherical equilibrium models is calculated. Based on several of the tests, the data are inconsistent with the models at the approximately 2.4 sigma level. The possibility that substructure is important in this cluster is therefore considered. It is found that a model that is spherically symmetric at large radii, and clumpy at small radii, is more consistent with the kinematical data. The locations and the velocities of the brighter cluster galaxies also lend support to this hypothesis. Such a model can also explain why Hydra I does not lie along the L(x)-sigma relation for galaxy clusters. 42 references.

A Search for Features in Early-Type Galaxies

Abstract: We are conducting a search for dust lanes, incipient stellar disks and bars, and other deviations from elliptical symmetry in a sample ~ 250 early-type galaxies. Division by a model galaxy image is a very powerful enhancement technique for this type of work.

Two blue arcs associated with the cD galaxy of Abell 963

Abstract: Two blue arcs associated with the cD galaxy in Abell 963 have been found. They are different in physical length, angle subtended, and distance from the nucleus of the cD, are on opposite sides of the cD galaxy, and both arcs appear concentric about the nucleus. The arcs are patchy and extremely blue, having colors bluer than the bluest members of the Abell 963 cluster. The cD galaxy is highly elliptical, epsilon roughly 0.5, with one, possibly both arcs, being bisected by the major axis of the cD. It is suggested that the most likely mechanism for the origin of the arcs is gravitational lensing of a high-redshift galaxy by the cD galaxy and the associated cluster core. 23 references.

The Kinematics and Dynamics of the Rich Cluster of Galaxies Abell 539

Abstract: A sample of 289 redshifts within 10 deg of the center of the cluster A539 have been obtained in order to investigate the cluster kinematics and dynamics. Within 1 Mpc of the center, the physical parameters of A539 are found to be typical of those of rich clusters. It is shown that early-type galaxies are more concentrated toward the cluster center and that the velocity distributions of early-type and late-type galaxies differ marginally.

Peculiar velocities of cD galaxies - MX spectroscopy of Abell 1795

Abstract: Spectroscopic observations of galaxies in the Abell 1795 field have been obtained using the MX multiple-object spectrograph on the Steward Observatory 2.3 m telescope. Redshifts are presented for 46 galaxies, including 41 cluster members. It is found that the A1795 cD galaxy is not at rest in the cluster gravitational potential well; it has a peculiar radial velocity, cz, of 365 km/s, and the hypothesis that the mean cluster velocity is as large as the cD's velocity can be rejected at the 99.5 percent confidence level. This conclusion is supported by spectroscopic data for the 'cooling flow' gas found in the central region of the cluster; this gas, except for the portion coincident with the cD nucleus, lies at the velocity derived for the cluster mean. It is suggested that current models of the formation of cD galaxies are unlikely to account for the large peculiar velocities of the cD galaxies in A1795 and A2670 unless substantial subclustering is still present. However, the available data show no evidence for velocity subclustering in either A1795 or A2670.

Co and H2 in Galaxies

Abstract: Matter in the universe consists mainly of hydrogen (90 per cent) and helium (10 per cent) to which is added a very small amount of heavier elements, mostly carbon, nitrogen and oxygen. In galaxies the major constituent, hydrogen, is found in a variety of forms: a. ionized atomic (HII) with typical electron temperatures Te = 104 K and typical densities ne = 10 - 100 cm−3, observed by recombination line emission at visual, near infrared and radio wavelengths. HII represents a small fraction of all hydrogen because it needs relatively rare OB stars for its excitation. b. neutral atomic (HI) with a typical spin temperature Ts = 100 K and a typical density nH = 1 – 10 cm−3, observed by its hyperfine structure radio line at 21.1 cm. HI is pervasive in galaxies; it usually extends beyond the optical boundaries of galaxies. The HI content of galaxies is generally related to Hubble type in the sense that the fraction of total mass represented by HI increases from early type galaxies (very low in E, SO galaxies) to later type galaxies (high in Sc, Ir galaxies). Here it should be noted that the actual nature of the atomic (neutral and ionized) is more complicated than sketched here: see a recent review by Kulkarni and Heiles (1987). c. neutral molecular (H2) with typical temperatures Tk = 10 – 30 K and a typical density n(H2) = 103 cm−3. H2 is pervasive in galaxies, but details of its correlation with galaxy type and its distribution in galaxies is still uncertain due to observational difficulties as will be discussed below. d. part of molecular compounds (e.g. OH, CH, HCN, H2CO, NH3 etc). Only a minute fraction of all hydrogen is locked up in these compounds which are usually closely associated with H2 concentrations.

ESO400-G43, a forming galaxy?

Abstract: Blue compact galaxies (BCGs) are characterized by their compact appearance and very blue colours1,2 indicative of a high star-formation rate. The metal abundances are low, suggesting that the present rate of star formation cannot have lasted for very long3 (unless the gas is being replenished). These galaxies are thus either truly young or their star formation takes place in short bursts3,4. ESO400-G43 ( = 2034–356) is one of the brightest and largest BCGs known. Observations in the 21-cm line with the Very Large Array (VLA) of the National Radio Astronomy Observatory reveal a massive (5×109 M⊙) slowly rotating H I halo. Optical observations obtained at the European Southern Observatory (ESO) show that the morphology and spectral properties are consistent with a predominantly young stellar population and an extremely low mass to light ratio (M/LB = 0.1). The luminous stars seem to be concentrated in a rapidly spinning central disk. Dark matter is dominating the mass at large radii.

Surface photometry of southern elliptical galaxies

Abstract: The results of a surface photometry survey for 131 elliptical galaxies in the southern hemisphere are presented. In this paper isophotal maps and major-axis profiles are shown, deriving for each galaxy in the sample structural parameters using the de Vaucouleurs law as useful parametric descriptor of the light distribution of elliptical galaxies. 61 references.

High spatial resolution imaging of some of the distant 3CR galaxies

Abstract: Deep, high spatial resolution imaging of several sources from the high-redshift 3CR galaxy sample is presented. Very complex and unexpected morphologies are found. All the galaxies observed so far are resolved, and most of them show multimodal sources. Significant color differences for the components of each galaxy are measured. An interpretation in terms of gravitational amplification/lensing by foreground galaxies or galactic clusters is proposed for 3C 238, 3C 241, and 3C 305.1, 3C 238 being the strongest candidate. The complexity of the 3CR galaxies like 3C 356, which includes a compact object, and 3C 326.1 shows that they are not normal ellipticals and their use as standard candles to test for galaxy evolution is therefore questionable. 29 references.

Imaging of very distant 3CR galaxies - high spatial resolution data for seven galaxies with z between 1. 176 and 1. 841

Abstract: This report continues a series of papers discussing a complete high spatial resolution imaging survey of the highest redshift 3CR radio galaxies. CCD observations of seven 3CR galaxies with redshifts between 1.176 and 1.841 are presented. Excellent seeing conditions facilitated resolution of most of the galaxies into multiple components. Two of the galaxies are located less than 4 arcsec from a foreground bright galaxy; it is suggested that they may be gravitationally amplified by more than one magnitude. One of the objects, 3C 194 at z = 1.779, is proposed as a gravitational lens candidate. For the other galaxies observed, different interpretations are considered. The use of the high-redshift 3CR radio-galaxies as standard candles for cosmological purposes without further precautions is questioned. 30 references.

A Possible Candidate of Arclike Structure in a Southern Cluster of Galaxies

Abstract: Observations of an elongated, arc-shaped structure found in a new southern rich cluster of galaxies at z = 0.316 are reported. The structure is concave toward a major cluster member and is bluer than most galaxies in the cluster. The projected image of the structure is located near a close, possibly merging or interacting pair of galaxies at z = 0.328. Three possible explanations are briefly discussed: (1) accidental superposition of objects, (2) disrupted arm or tail of an interacting pair, and (3) gravitational lensing of a background object. 13 references.

Galaxies as tracers of the mass distribution

Abstract: We review theoretical arguments which suggest that galaxies may be more strongly clustered than the mass distribution These ideas can be checked by testing whether the strength of galaxy clustering depends on the properties of the tracers (eg their luminosities, morphological type, etc) and whether biases extend to large scales The IRAS sample may provide strong constraints on large-scale clustering We present preliminary results from a redshift survey of IRAS galaxies which indicate no significant correlations on scales ≥ 15h−1Mpc

A red envelope around a dominant elliptical galaxy in an X-ray selected poor cluster

Abstract: A photometric and spectroscopic study of the optical counterpart of the X-ray source 1E 1111.9-3754 has revealed a poor cluster of galaxies dominated by a very luminous giant elliptical. Three-color surface photometry of this galaxy shows that the elliptical body is surrounded by a large envelope with colors redder than the galaxy. The formation of this system in a high velocity dispersion poor cluster is briefly discussed.