Zwicky Clusters Research Articles

Relationship of galaxies from the second Byurakan survey to Zwicky clusters. II. Discussion

We analyze the data presented in a previous paper by Gyulzadyan and Petrosian, and discuss the results of a statistical investigation of the relationship between SBS galaxies and Zwicky clusters. The main results are that SBS galaxies follow the overall galaxy distribution in clusters and they do not avoid any type of Zwicky cluster. There is a significantly higher probability of finding SBS galaxies occurring in medium compact clusters than in open clusters. They also follow the well-established morphology-density relation. Earlier morphological type, higher luminosity, larger linear size, and redder SBS galaxies tend to be found in clusters with higher compactness, or in more compact regions of the clusters. The number distribution of SBS galaxies in Zwicky open clusters probably follows the distribution of normal galaxies. The number distribution of SBS galaxies in medium compact and compact clusters shows two-maxima structure.

The relation of Second Byurakan Survey galaxies with Zwicky clusters. I. Data

In the region of the sky covered by both the Second Byurakan Survey (SBS) and the Zwicky Catalog of Galaxies and Clusters of Galaxies (CGCG) 892 of the 1677 active galaxies lie within the contours of Zwicky clusters. Data on these galaxies and the corresponding clusters are listed in tables according to whether they are actual, probable, or random members of clusters or are projected on them.

Nature and environment of Very Luminous Galaxies

The most luminous galaxies in the blue passband have a larger correlation amplitude than L * galaxies. They do not appear to be preferentially located in rich clusters or groups, but a significant fraction of them seem to be in systems which include fainter members. We present an analysis of fields centered on 18 Very Luminous Galaxies ($M_B \le -21$) selected from the Southern Sky Redshift Survey 2, based on new observations and public data of the 2dF Galaxy Redshift Survey; we present also additional data on a CfA VLG and on Arp 127. We find that all the selected VLGs are physically associated with fainter companions. Moreover, there is a relation between the VLG morphology (early or late) and the dynamical properties of the system, which reflects the morphology–density relation. 6 out of the 18 SSRS2 VLGs are early type galaxies: 2 are in the center of rich Abell clusters with velocity dispersion $\sigma \sim 600$ km s -1 , and the other 4 are in poor clusters or groups with $\sigma \sim 300$. The VLG extracted from the CfA catalog is also an elliptical in a Zwicky cluster. The remaining 2/3 of the sample are late–type VLGs, generally found in poorer systems with a larger spread in velocity dispersion, from ~100 up to ~750 km s -1 . The low velocity dispersion, late–type VLG dominated systems appear to be analogous to our own Local Group. The possibile association of VLG systems with dark matter halos with mass comparable to rich groups or clusters, as suggested by the comparable correlation amplitude, would imply significant differences in the galaxy formation process. This work also shows that observing fields around VLGs represents an effective way of identifying galaxy systems which are not selected through other traditional techniques.

The ROSAT Brightest Cluster Sample -- I. The compilation of the sample and the cluster log N--log S distribution

We present a 90 per cent flux-complete sample of the 201 X-ray-brightest clusters of galaxies in the northern hemisphere (δ ≥ 0°), at high Galactic latitudes (|b| ≥ 20°), with measured redshifts z ≤ 0.3 and fluxes higher than 4.4 × 10−12 erg cm−2 s−1 in the 0.1–2.4 keV band. The sample, called the ROSAT Brightest Cluster Sample (BCS), is selected from ROSAT All-Sky Survey data and is the largest X-ray-selected cluster sample compiled to date. In addition to Abell clusters, which form the bulk of the sample, the BCS also contains the X-ray-brightest Zwicky clusters and other clusters selected from their X-ray properties alone. Effort has been made to ensure the highest possible completeness of the sample and the smallest possible contamination by non-cluster X-ray sources. X-ray fluxes are computed using an algorithm tailored for the detection and characterization of X-ray emission from galaxy clusters. These fluxes are accurate to better than 15 per cent (mean 1σ error). We find the cumulative log N–log S distribution of clusters to follow a power law κSα with α = 1.31+0.06−0.03 (errors are the 10th and 90th percentiles) down to fluxes of 2 × 10−12 erg cm−2 s−1, i.e. considerably below the BCS flux limit. Although our best-fitting slope disagrees formally with the canonical value of −1.5 for a Euclidean distribution, the BCS log N–log S distribution is consistent with a non-evolving cluster population if cosmological effects are taken into account. Our sample will allow us to examine large-scale structure in the northern hemisphere, determine the spatial cluster–cluster correlation function, investigate correlations between the X-ray and optical properties of the clusters, establish the X-ray luminosity function for galaxy clusters, and discuss the implications of the results for cluster evolution.

A Search for Large Voids from Combined Samples of Galaxy Clusters and Galaxies

This paper is part of a more extensive study of the large voids in spatial volumes both wide and deep. Three samples of optical tracers with spectroscopically measured redshifts in a volume with b≥30° and z≤0.14 have been extracted from the catalogue of Lebedev and Lebedeva (1986) and the NASA/IPAC Extragalactic Database (NED): (1)a homogeneous sample of 277 rich Abell clusters(2)an inhomogeneous sample of 969 objects: rich and poor Abell clusters, Zwicky clusters, other clusters, and groups(3)a sample of 18 623 NED galaxies.

Optical spectroscopy of the ROSAT X-ray brightest clusters - II

The results from the first stage of an optical follow-up study of the X-ray brightest clusters of galaxies detected in the ROSAT All-Sky Survey (RASS) are presented. The redshifts of the central galaxies in 29 of the X-ray brightest Abell and Zwicky clusters in the RASS have been measured using the Faint Object Spectrograph on the Isaac Newton Telescope. Approximately 40 per cent of the central galaxy spectra obtained show strong optical line emission. In several cases this emission is quite spectacular

Statistical association of QSO's with foreground galaxy clusters

view Abstract Citations (44) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Statistical Association of QSO's With Foreground Galaxy Clusters Rodrigues-Williams, Liliya L. ; Hogan, Craig J. Abstract in the directions of foreground galaxy clusters. QSO's are taken from the Large Bright QSO Survey (LBQS) between 1.4 <= z <= 2.2 with a limiting magnitude of m_B_ = 18.5. Foreground clusters are regions within 6 Zwicky radii of small Zwicky clusters at a characteristic redshift of about z~0.2, covering about 40% of the total area surveyed (304 square degrees). The overdensity, defined as the ratio of the number density of QSO's in the directions of clusters ("association QSO's") to that in the remainder of the fields ("background QSO's"), is equal to 1.7, and formally differs from unity at 4.7 σ significance. The observed overdensity probably is not due to statistical variation in QSO density, intrinsic QSO-QSO and/or cluster-cluster autocorrelations, or patchy Galactic obscuration. We thus interpret this observation as being due to statistical gravitational lensing of background QSO's by galaxy clusters. However, this amplitude of overdensity behind clusters cannot be accounted for in any cluster lensing model if the background QSO number- magnitude counts are similar to the intrinsic (unlensed) counts, and is implausible in any conventional model of cosmic mass distribution. Publication: The Astronomical Journal Pub Date: February 1994 DOI: 10.1086/116866 Bibcode: 1994AJ....107..451R Keywords: Autocorrelation; Cosmology; Cross Correlation; Galactic Clusters; Galactic Mass; Gravitational Lenses; Mass Distribution; Quasars; Red Shift; Stellar Models; Error Analysis; Sky Surveys (Astronomy); Astrophysics; QUASARS: GENERAL; GALAXIES: DISTANCES AND REDSHIFTS; GALAXIES: CLUSTERING full text sources ADS |

Discovery of two radio galaxies in the Zwicky Cluster 1437.3 + 6436

Two radio galaxies were serendipitously discovered in the Zwicky Cluster 1437.3+6436. One radio galaxy is a resolved point source. The other radio galaxy consists of jets that extend from a resolved core and eventually reach a large region of extended emission in a direction away from the cluster center. From the Palomar Observatory Sky Survey prints, it is found that the optical counterparts of these radio sources are elliptical galaxies. The radio and optical properties of these galaxies are consistent with those of galaxies in other clusters

Galaxy and cluster redshift observations in the Sextans-Leo region

Redshift observations of 30 clusters in the direction of the Sextans-Leo supercluster candidate are reported. The observations are part of a program which involves mapping the universe's large-scale structure, and include North Galactic Cap Abell clusters, Abell clusters that have only been partially observed, and unmeasured poor Zwicky clusters. Three large superclusters are identified in the region which surround an apparent void that is open on one side towards the galaxy void in Bootes. The minimum dimensions of the void are given, and one of the superclusters is identified based on it resemblance to Coma/A1367. The emptiness of the Bootes void and the void of Bahcall and Soneira (1982) are redefined by the positions determined for five clusters observed in other portions of the northern cap. Additionally, some galaxies appear to be within the bounds of the Sextans-Leo void.

On the connection between Seyfert galaxies and clusters

To identify Seyfert galaxies that are members of clusters, the sample of known Seyfert galaxies (464 objects) is tested against the Zwicky, Abell, and southern clusters. On the basis of the criteria adopted in the paper, 67 Seyfert galaxies are selected as probable members of Zwicky clusters, 15 as members of Abell clusters, and 18 as members of southern clusters. Lists of these objects are given.

Markarian Galaxies and Zwicky Clusters

From 1344 Markarian galaxies lying in the same area covered by Markarian survey and CGCG, 592 are positioned within the contours of Zwicky clusters. On the basis of these data statistical investigation of the relation of Markarian galaxies with Zwicky clusters is carried out. Markarian galaxies take part in the tendency of clustering of galaxies and they lie in any type of Zwicky clusters. Markarian galaxies coincide with greater probability with medium compact clusters than with open ones where they follow the distribution of normal galaxies. In medium compact and compact clusters they appear near the centres of concentration of galaxies but probably not in their dense cores.

The cluster-cluster correlation function

The clustering properties of the Abell and Zwicky cluster catalogs are studied using the two-point angular and spatial correlation functions. The catalogs are divided into eight subsamples to determine the dependence of the correlation function on distance, richness, and the method of cluster identification. It is found that the Corona Borealis supercluster contributes significant power to the spatial correlation function to the Abell cluster sample with distance class of four or less. The distance-limited catalog of 152 Abell clusters, which is not greatly affected by a single system, has a spatial correlation function consistent with the power law Xi(r) = 300r exp -1.8. In both the distance class four or less and distance-limited samples the signal in the spatial correlation function is a power law detectable out to 60/h Mpc. The amplitude of Xi(r) for clusters of richness class two is about three times that for richness class one clusters. The two-point spatial correlation function is sensitive to the use of estimated redshifts.

A possible 300 megaparsec filament of clusters of galaxies in Perseus-Pegasus

view Abstract Citations (89) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A possible 300 megaparsec filament of clusters of galaxies in Perseus-Pegasus. Batuski, D. J. ; Burns, J. O. Abstract In this paper, the results of redshift observations for Abell clusters with m10 less than 16.5 and medium-distant Zwicky clusters in a large region of the South Galactic Cap are presented. The region contains a possible filament of galaxies and galaxy clusters which includes the Perseus-Pisces Supercluster and has a total apparent length of over 300/h Mpc. The observed distribution of three-dimensional cluster alignments is compared with that for a random distribution of clusters constrained to have the same two-point spatial correlation function as the Abell clusters. The Kolmogorov-Smirnov test indicates less than 0.3 percent probability that the apparent filament could occur in the 'constrained random' samples. Some of the possible implications that the existence of such large structures might have for the more popular theories on the formation of galaxies and clusters are also discussed. Publication: The Astrophysical Journal Pub Date: December 1985 DOI: 10.1086/163677 Bibcode: 1985ApJ...299....5B Keywords: Cosmology; Galactic Clusters; Red Shift; Correlation; Galactic Evolution; Statistical Tests; Astrophysics full text sources ADS | data products SIMBAD (56) NED (48)

A connection between galaxy probabilities in zwicky clusters counting distributions in particle physics and quantum optics

We have evaluated the probability distribution for finding n galaxies in a Zwicky cluster for six regions of the sky for a depth sample corresponding to 15 × 10 3 km/s < V s < 60 × 10 3 km/s red-shift velocity. Two regions differ from the other four by having a significantly greater high multiplicity tail and a lower peak value. In our view these tails correspond to ongoing gravitational coalescence of clusters, which is more effective in more heterogeneous regions. We obtain by subtraction a distribution to be identified with the original cluster distribution. The form of this distribution belongs to a general class characteristic of chaotic production mechanisms already identified in photoelectron counts from thermal sources and in hadronic charged particle multiplicity distributions. The possible nature of this universal mechanism is discussed.

The structure of 4C radio galaxies in poor clusters

view Abstract Citations (35) References (79) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The structure of 4C radio galaxies in poor clusters. Burns, J. O. ; Gregory, S. A. Abstract VLA radio maps at 6 and 20 cm of 4C sources in poor Zwicky clusters of galaxies are presented. The data base and the observations are described, and total intensity radio maps are presented along with brief descriptions of individual source structures. The rates of occurrence of compact nuclear cores and radio jets are discussed, and the correlations between the total and core flux densities and between core radio powers and the detection of jets are described. The cluster environment of these galaxies is analyzed, and the distribution of hot gas as viewed from the Einstein observatory is compared with extended radio features. Publication: The Astronomical Journal Pub Date: September 1982 DOI: 10.1086/113210 Bibcode: 1982AJ.....87.1245B Keywords: Astronomical Maps; Galactic Clusters; Galactic Structure; Radio Astronomy; Radio Galaxies; Antenna Arrays; Data Reduction; Gas Temperature; Heao 2; Mass Distribution; Plasma Jets; Radio Telescopes; Astrophysics full text sources ADS | data products NED (25)

Redshifts, first and second order clustering properties, and refined radio parameters of 4C radio galaxies in poor clusters

view Abstract Citations (15) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Redshift, first and second order clustering properties, and refined radio parameters of 4C radio galaxies in poor clusters. Gregory, S. A. ; Burns, J. O. Abstract By determining 16 new redshifts and confirming two others, we have completed distance determinations for a complete sample of 22 4C radio galaxies in poor Zwicky clusters. Using the new redshifts, we have refined the absolute radio parameters such as the radio powers at 2.7 GHz (P2.7) and source sizes. We have also determined richness, compactness, and Bautz-Morgan types for the clusters by carefully examining the cluster fields on the Palomar Sky Survey. We find that has a similar distribution to that of rich clusters. We also find a weak correlation of P2.7 with the Bautz-Morgan classification which measures properties of the dominant cluster galaxy. This sample of poor clusters indicates that the radio galaxy phenomenon is related more to the properties of the central, dominant galaxies than to the extended cluster environment. This agrees with previous results for Abell clusters. We further investigate superclustering near the poor Zwicky clusters; a list of possible superclusters composed of Abell and Zwicky clusters is presented. One of these superclusters probably contains a quasar. Publication: The Astrophysical Journal Pub Date: April 1982 DOI: 10.1086/159837 Bibcode: 1982ApJ...255..373G Keywords: Galactic Clusters; Radio Galaxies; Red Shift; Classifications; Galactic Structure; Luminosity; Astrophysics full text sources ADS | data products NED (63) SIMBAD (4)

X-ray emission around radio galaxies in non-Abell clusters - A possible physical link between environment and nonthermal radio emission

X-ray observations of a sample of 11 4C radio galaxies in clusters with z< or approx. =0.1 were performed with the IPC (resolution FWHMapprox.1'.5) on the Einstein Observatory. The sample galaxies lie in the directions of non-Abell Zwicky clusters; these clusters are generally poor, ranging in effective Abell richness class from < or approx. =0 to 1. In 10 out of the 11 observed fields 1--3 keV emission was detected. In nearly every case, the X-ray emission is centered on the radio galaxy; 5 out of 10 of the X-ray sources are resolved with HWHM of 70--300 kpc. The X-ray luminosities are (1--60) x 10/sup 42/ ergs s/sup -1/ (H/sub 0/ = 75 km s/sup -1/ Mpc/sup -1/), generally less than the richer Abell clusters and undetectable with previous satellites. Examinations of the optical fields and preliminary velocity data suggest that most of the radio sources are associated with dominant galaxies which are at rest at the gravitational centers of the clusters. Internal relativistic particle and magnetic field pressures of the relaxed outer radio structures are on the same order as the thermal pressure produced by the X-ray emitting gas. We argue that this class of radio source is confinedmore » (and possibly triggered) by gas accumulated at the cluster centers. The X-ray emission is a cosmic signpost indicating the presence of large quantities of gas around the central radio galaxies. Recent radio observations indicate that the probability of galaxy radio emission is much higher for cluster galaxies than for very isolated galaxies; these new X-ray observations of poor clusters combined with previous data on Abell clusters suggest that the presence of cluster gas is the important factor in determining the link between cluster environment and radio emission.« less

HEAO A-2 observations of non-Abell Zwicky clusters containing extended radio sources

Burns and Owen's sample of 25 4C radio sources which coincide with Zwicky clusters of galaxies has been searched for X-ray emission using the HEAO 1 A-2 experiment. X-ray emission was detected from five sources at the 3sigma level, two of which exceeded 5sigma. Positions and 90% X-ray error boxes are given for each of the five sources detected. The clusters surveyed are non-Abell clusters which would generally not be expected to be detectable with the A-2 experiment. The search for X-ray emission was prompted by the knowledge of the existence of extended radio sources in the clusters. The relaxed structure of these sources implies the presence of a relatively dense intracluster medium which is expected to produce thermal bremsstrahlung X-ray emission.

Structure of superclusters and supercluster formation

The study of the spatial distribution of galaxies and clusters of galaxies in the southern galactic hemisphere is continued using Zwicky clusters as principal tracers of the large-scale structure. The densest condensations of matter, rich clusters, containing many radio sources and a high percentage of elliptical and S0 galaxies have been joined by slightly curved or straight chains of clusters of galaxies. Chains are moderately rich in E and S0 galaxies and contain radio sources. The planes joining neighbouring chains are also populated by galaxies. Galaxies form thin strata here, containing no radio galaxies and a very low percentage of elliptical and S0 galaxies. The whole picture resembles cells. One cell wall with surrounding cluster chains can be taken for a supercluster. All clusters of galaxies and most galaxies are located in superclusters. Neighbouring superclusters are in contact and contain common elements. The space inside the cell is void of clusters and almost void of galaxies. Arguments have been given suggesting that superclusters formed prior to the formation of galaxies or simultaneously with them.

Radio sources in Zwicky clusters of galaxies. II - Detailed interferometer observations and analysis

Interferometer observations of a sample of 23 4C sources that spatially coincide with Zwicky clusters of galaxies are reported. These sources are used to examine the nature of extended radio emission from galaxies in poor clusters. The majority of these radio sources exhibit some signs of morphological distortion (i.e., head-tail structure), which is indicative of dynamic interaction with a relatively dense intracluster gas. The properties of the Zwicky cluster sources are compared with a similar radio survey of rich Abell clusters. The results suggest that the environments around radio galaxies (i.e., density and temperature of the intracluster gas) are similar in rich and poor clusters. The relative numbers of Abell and non-Abell/Zwicky cluster sources further indicate that most (60-100%) of the total population of intermediate-luminosity radio galaxies may be in clusters of various richnesses. A nonrigorous analysis of existing data on nearby radio galaxies suggests that most radio galaxies, including those in this sample, are in superclusters of galaxies; the implications of this result are briefly discussed.