Context: For the first time, spectroscopic
galaxy redshift surveys are
enabling galaxies to be studied with the nearest quasars. This allows
the dependence of the activity of a quasar on its environment to be
studied in a more extensive way than before.
Aims: We study the
spatial distribution of galaxies and properties of groups of galaxies in
the environments of low redshift quasars in the Sloan Digital Sky Survey
(SDSS). Our aim is to understand how the nearby quasars are embedded in
the local and global density field of galaxies and how the environment
affects quasar activity.
Methods: We analyze the environments of
nearby quasars using number counts of galaxies. We also study the
dependence of group properties on their distance to the nearest quasar.
The large-scale environments are studied by analyzing the locations of
quasars in the luminosity density field.
Results: Our study of
the number counts of galaxies in quasar environments shows an
underdensity of bright galaxies at a few Mpc from quasars. Groups of
galaxies with a quasar closer than 2 Mpc are also poorer and less
luminous than average. Our analysis of the luminosity density field
shows that quasars clearly avoid rich superclusters. Nearby quasars seem
to be located in the outskirts of superclusters or in the filaments
connecting them.
Conclusions: Our results suggest that quasar
evolution may be affected by density variations both on supercluster
scales and in the local environment.
A large sample of Abell clusters of galaxies,
selected for the likely
presence of a dominant galaxy, is used to study the dynamical properties
of the brightest cluster members (BCMs). From visual inspection of
Digitized Sky Survey images combined with redshift information we
identify 1426 candidate BCMs located in 1221 different redshift
components associated with 1169 different Abell clusters. This is the
largest sample published so far of such galaxies. From our own
morphological classification we find that ~92% of the BCMs in our sample
are early-type galaxies and 48% are of cD type. We confirm what was
previously observed based on much smaller samples, namely, that a large
fraction of BCMs have significant peculiar velocities. From a subsample
of 452 clusters having at least 10 measured radial velocities, we
estimate a median BCM peculiar velocity of 32% of their host clusters'
radial velocity dispersion. This suggests that most BCMs are not at rest
in the potential well of their clusters. This phenomenon is common to
galaxy clusters in our sample, and not a special trait of clusters
hosting cD galaxies. We show that the peculiar velocity of the BCM is
independent of cluster richness and only slightly dependent on the
Bautz-Morgan type. We also find a weak trend for the peculiar velocity
to rise with the cluster velocity dispersion. The strongest dependence
is with the morphological type of the BCM: cD galaxies tend to have
lower relative peculiar velocities than elliptical galaxies. This result
points to a connection between the formation of the BCMs and that of
their clusters. Our data are qualitatively consistent with the
merging-groups scenario, where BCMs in clusters formed first in smaller
subsystems comparable to compact groups of galaxies. In this scenario,
clusters would have formed recently from the mergers of many such groups
and would still be in a dynamically unrelaxed state.
Aims: We use the 2dF Galaxy Redshift Survey to
derive the luminosity
function (LF) of the first-ranked (brightest) group/cluster galaxies,
the LF of second-ranked, satellite, and isolated galaxies, and the LF of
groups of galaxies.
Methods: We investigate the LFs of different
samples in various environments: in voids, filaments, superclusters, and
supercluster cores. We compare the derived LFs with the Schechter and
double-power-law analytical expressions. We also analyse the
luminosities of isolated galaxies.
Results: We find a strong
environmental dependency by the luminosity functions of all populations.
The luminosities of first-ranked galaxies have a lower limit, depending
on the global environment (higher in supercluster cores and absent in
voids). The LF of second-ranked galaxies in high-density regions is
similar to the LF of first-ranked galaxies in a lower density
environment. The brightest isolated galaxies can be identified with
first-ranked galaxies at distances where the remaining galaxies lie
outside the observational window used in the survey.
Conclusions:
The galaxy and cluster LFs can be approximated by a double-power law.
The widely used Schechter function does not describe the bright end and
the bend of the LFs well. Properties of the LFs reflect differences in
the evolution of galaxies and their groups in different environments.
We present a morphological study of the two
richest superclusters from
the 2dFGRS (SCl 126, the Sloan Great Wall, and SCl 9, the Sculptor
supercluster). We use Minkowski functionals, shapefinders, and galaxy
group information to study the substructure of these superclusters as
formed by different populations of galaxies. We compare the properties
of grouped and isolated galaxies in the core region and in the outskirts
of superclusters. The fourth Minkowski functional V3 and the
morphological signature K1-K2 show a crossover
from low-density morphology (outskirts of supercluster) to high-density
morphology (core of supercluster) at mass fraction mf~0.7.
The galaxy content and the morphology of the galaxy populations in
supercluster cores and outskirts are different. The core regions contain
a larger fraction of early-type, red galaxies and richer groups than the
outskirts of superclusters. In the core and outskirt regions the fine
structure of the two prominent superclusters as delineated by galaxies
from different populations also differs. The values of the fourth
Minkowski functional V3 show that in the supercluster SCl 126
the population of early-type, red galaxies is more clumpy than that of
late-type, blue galaxies, especially in the outskirts of the
supercluster. On the contrary, in the supercluster SCl 9, the clumpiness
of the spatial distribution of galaxies of different type and color is
quite similar in the outskirts of the supercluster, while in the core
region the clumpiness of the late-type, blue galaxy population is larger
than that of the early-type, red galaxy population. Our results suggest
that both local (group/cluster) and global (supercluster) environments
are important in forming galaxy morphologies and colors (and determining
the star formation activity). The differences between the superclusters
indicate that these superclusters have different evolutional histories.
Aims: We extract groups of galaxies from the
SDSS Data Release 5 to
study the supercluster-void network and environmental properties of
groups therein. Groups of galaxies as density enhancements can be used
to determine the luminosity density field of the supercluster-void
network.
Methods: We use a modified friends-of-friends (FoF)
method with slightly variable linking lengths in transverse and radial
directions to eliminate selection effects and to reliably find as many
groups as possible. To determine the scaling of the linking length we
calibrated group sizes and mean galaxy number densities within groups by
shifting nearby groups to larger distances.
Results: Our final
sample contains 17 143 groups in the equatorial, and 33 219 groups in
the northern part of the DR5 survey. The group catalogue is available at
the CDS.
Conclusions: The mean sizes and velocity dispersions of
our groups practically do not change with their distance. This means
that the selection effects have been properly taken into account when
generating the group catalogue.
Full Table 3 is only available in electronic form at the CDS via
anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/479/927
Context: Superclusters are the largest systems
in the Universe to give
us information about the formation and evolution of structures in the
very early Universe. Our present series of papers is devoted to the
study of the morphology and internal structure of superclusters of
galaxies.
Aims: We study the morphology of the richest
superclusters from the catalogs of superclusters of galaxies in the 2dF
Galaxy Redshift Survey and compare the morphology of real superclusters
with model superclusters in the Millennium Simulation.
Methods:
We use Minkowski functionals and shapefinders to quantify the morphology
of superclusters: their sizes, shapes, and clumpiness. We generate
empirical models of simple geometry to understand which morphologies
correspond to the supercluster shapefinders (Appendix A).
Results:
Rich superclusters have elongated, filamentary shapes with
high-density clumps in their core regions. The clumpiness of
superclusters is determined using the fourth Minkowski functional V_3.
In the K_1-K2 shapefinder plane the morphology of
superclusters is described by a curve which is characteristic of
multi-branching filaments as shown by our empirical models. We found
several differences between observed and model superclusters. The curves
of the fourth Minkowski functional V3 for observed and model
superclusters have different shapes indicating that their structure is
different. The values of V3 for the supercluster SCL126 (the
Sloan Great Wall) show that this supercluster has a very high density
core which is absent in other superclusters. The values of the
shapefinders H1-H3 and K1 and
K2 for observed superclusters have much larger scatter than
for model superclusters. The differences between the fourth Minkowski
functional V3 for the bright and faint galaxies in observed
superclusters are larger than in simulated superclusters.
Conclusions:
Our results show how the Minkowski functionals and
shapefinders can be used to describe the morphology of superclusters:
their shapes, sizes and clumpiness. The shapes of observed superclusters
are more diverse than the shapes of simulated superclusters. The larger
scatter of the fourth Minkowski functional V3 for the bright
and faint galaxies for observed superclusters compared to simulated
superclusters is an indication that the clumpiness of bright and faint
galaxies in models does not reflect well the clumpiness of different
galaxies in observed superclusters. Our results suggest also that the
volume covered by the Millennium Simulations may be too small to
properly describe the large morphological variety of superclusters.
We extract groups of galaxies from the SDSS
Data Release 5 to study the
supercluster-void network and environmental properties of groups
therein. Groups of galaxies as density enhancements can be used to
determine the luminosity density field of the supercluster-void network.
We use a modified friends-of-friends (FoF) method with slightly variable
linking lengths in transverse and radial directions to eliminate
selection effects and to reliably find as many groups as possible. To
determine the scaling of the linking length we calibrated group sizes
and mean galaxy number densities within groups by shifting nearby groups
to larger distances.
Our final sample contains 17143 groups in the equatorial (E), and 33219
groups in the northern (N) part of the DR5 survey. The mean sizes and
velocity dispersions of our groups practically do not change with their
distance. This means that the selection effects have been properly taken
into account when generating the group catalogue.
(4 data files).
We study the morphology of galaxy populations
of the richest
superclusters from the catalogue of superclusters of galaxies in the 2dF
Galaxy Redshift Survey using the luminosity density distribution and
Minkowski functional V3. We compare the properties of grouped and
isolated galaxies in regions of different density in superclusters. We
find that in high-density cores of rich superclusters there is an excess
of early type, passive galaxies, among galaxies in groups and clusters,
as well as among those which do not belong to groups, while in lower
density outer regions there are more blue, star-forming galaxies both in
groups and among those galaxies which do not belong to groups. This also
shows that the galaxy content of groups depends on the environment where
the groups reside in. The density distributions and the behaviour of the
Minkowski functional V3 for different superclusters show that
substructures in superclusters as traced by different populations of
galaxies are very different. Our results show that both local
(group/cluster) and global (supercluster) environments are important in
forming galaxy morphologies and star formation activity. The presence of
a high density core with X-ray clusters and a relatively small fraction
of star-forming galaxies in the supercluster SCL126 may be an indication
that this supercluster has started its evolution earlier than the
supercluster SCL9.
Context: Superclusters are the largest
systems in the Universe to give
us information about the very early Universe. Our present series of
papers is devoted to the study of the properties of superclusters of
galaxies from the 2dF Galaxy Redshift survey.
Aims: We use
catalogues of superclusters of galaxies from the 2dF Galaxy Redshift
Survey to compare the properties of rich and poor superclusters. In
particular, we study the properties of galaxies (spectral types,
colours, and luminosities) in superclusters.
Methods: We compare
the distribution of densities in rich and poor superclusters, and the
properties of galaxies in high and low-density regions of rich
superclusters, in poor superclusters, and in the field. In superclusters
and in the field, we also compare the properties of galaxies in groups,
and the properties of those galaxies which do not belong to any group.
Results: We show that in rich superclusters the values of the
luminosity density smoothed on a scale of 8 h-1 Mpc are
higher than in poor superclusters: the median density in rich
superclusters is δ ≈ 7.5 and in poor superclusters δ ≈
6.0. Rich superclusters contain high-density cores with densities
δ > 10, while in poor superclusters such high-density cores are
absent. The properties of galaxies in rich and poor superclusters and in
the field are different: the fraction of early type, passive galaxies in
rich superclusters is slightly higher than in poor superclusters, and is
the lowest among the field galaxies. Most importantly, in high-density
cores of rich superclusters (δ > 10), there is an excess of
early type, passive galaxies in groups and clusters, as well as among
those which do not belong to any group. The main galaxies of
superclusters have a rather limited range of absolute magnitudes. The
main galaxies of rich superclusters have higher luminosities than those
of poor superclusters and of groups in the field.
Conclusions:
.Our results show that both the local (group/cluster) environments and
global (supercluster) environments influence galaxy morphologies and
their star formation activity.
Aims:We use the 2dF Galaxy Redshift Survey
data to compile catalogues of
superclusters for the Northern and Southern regions of the 2dFGRS,
altogether 543 superclusters at redshifts 0.009 ≤ z ≤ 0.2.
Methods:
We analyse methods of compiling supercluster catalogues and
use results of the Millennium Simulation to investigate possible
selection effects and errors. We find that the most effective method is
the density field method using smoothing with an Epanechnikov kernel of
radius 8 h-1 Mpc.
Results: We derive positions of the
highest luminosity density peaks and find the most luminous cluster in
the vicinity of the peak, this cluster is considered as the main cluster
and its brightest galaxy the main galaxy of the supercluster. In
catalogues we give equatorial coordinates and distances of superclusters
as determined by positions of their main clusters. We also calculate the
expected total luminosities of the superclusters.
Catalogue is only available in electronic form at the CDS via anonymous
ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/462/811
Aims:We investigate properties of
superclusters of galaxies found in of
the 2dF Galaxy Redshift Survey, and compare them with properties of
superclusters from the Millennium Simulation.
Methods: We study
the dependence of various characteristics of superclusters on their
distance from the observer, on their total luminosity, and on their
multiplicity. The multiplicity is defined by the number of Density Field
(DF) clusters in superclusters. Using the multiplicity we divide
superclusters into four richness classes: poor, medium, rich and
extremely rich.
Results: We show that superclusters are
asymmetrical and have a multi-branching filamentary structure, with the
degree of asymmetry and filamentarity being higher for the more luminous
and richer superclusters. The comparison of real superclusters with
Millennium superclusters shows that most properties of simulated
superclusters agree very well with real data, the main differences being
in the luminosity and multiplicity distributions.
We identified Brightest Cluster Members (BCM)
on DSS images of 1083
Abell clusters, derived their individual and host cluster redshifts from
literature and determined the BCM ellipticity. Half the BCMs move at a
speed higher than 37% of the cluster velocity dispersion scl, suggesting
that most BCMs are part of substructures falling into the main cluster.
The IC 65 group (z = 0.0089) of four late type
galaxies IC 65, UGC
608, UGC 622, and PGC 138291 has been studied earlier in the 21 cm HI
line by van Moorsel (1983, A&AS, 54, 1), who found disturbed HI
envelopes of bright group members, and detected a new HI-rich LSB
galaxy.
We create a new catalogue of groups and
clusters, applying the
friends-to-friends method to the 2dF GRS final release. We investigate
various selection effects due to the use of a magnitude limited sample.
For this purpose we follow the changes in group sizes and mean galaxy
number densities within the groups when shifting nearby observed groups
to larger distances. We study the distribution of sizes of dark matter
haloes in N-body simulations and compare properties of these haloes and
the 2dF groups.
(6 data files).
Tables contain data on superclusters, selected
from the 2dFGRS survey.
Catalogues consist of four lists, two for each Galaxy hemisphere, the
main lists A for superclusters up to distance 520Mpc/h, and
supplementary lists B for more distant systems. The lists are ordered
according to increasing RA, a common id-numeration for lists A and B.
Distance and sizes are given in Mpc/h, luminosities in Solar units
L{sun}/h^2, where h is the Hubble constant in units of
100km/s/Mpc
(4 data files).
Tables contain data on superclusters, selected
from SDSS DR4
high-declination region data. Method to select superclusters is
described in the paper and in a forthcomming paper (Einasto et al.,
"Superclusters of galaxies from the 2dF redshift survey. I. The
catalogue", in press) Table A contains the main catalogue with
superclusters located at distances up to 520Mpc/h, Table B contains
supplementary superclusters at distances over 520Mpc/h.
(2 data files).
Aims.We compile a supercluster sample using
the Sloan Digital Sky Survey
Data Release 4, and reanalyse supercluster samples found for the 2dF
Galaxy Redshift Survey and for simulated galaxies of the Millennium
Run.
Methods: .We find for all supercluster samples Density Field
(DF) clusters, which represent high-density peaks of the class of Abell
clusters, and use median luminosities of richness class 1 DF-clusters to
calculate relative luminosity functions.
Results: .We show that
the fraction of very luminous superclusters in real samples is about
five times greater than in simulated samples.
Conclusions:
.Superclusters are generated by large-scale density perturbations that
evolve very slowly. The absence of very luminous superclusters in
simulations can be explained either by incorrect treatment of
large-scale perturbations, or by some yet unknown processes in the very
early Universe.
We inspected DSS images of 1083 Abell clusters
likely to have a dominant
galaxy, and derived accurate positions for BCM candidates, as well as
ellipticities using IRAF's ellipse. We retrieved the BCM's basic
parameters from NED, and extracted cluster mean redshifts, z_{cl}, and
velocity dispersions, σ_{cl}, from the compilation maintained by
two of us (Andernach et al.005, ASPCS 329, 283). We include only
clusters with at least 10 measured redshifts, yielding a sample of 385
BCMs in 326 Abell clusters. For these we derived the relative velocity
offset, v_{off}/σ_{cl} = (v_{BCM} - cz_{cl})/(1 +
z_{cl})/σ_{cl} , where v_{BCM} is the BCM radial velocity. Half of
the BCMs in our sample move at peculiar velocities above 0.37
σ_{cl}, with a trend for a smaller v_{off}/σ_{cl} in richer
clusters which is expected if the latter are dynamically more evolved.
For a sample of 980 BCMs the median ellipticity of the BCM's outer
envelopes <ɛ> rises with Abell richness, such that
<ɛ>=0.19 for the 559 R=0 clusters, <ɛ>=0.22
for 276 R=1 clusters, and <ɛ>=0.26 for 145 R ≥ 2
clusters. A Kolmogorov-Smirnov test for the ellipticity distributions
yields probabilities of p=0.016 for the R=0 and R=1 samples, and
p<0.0005 for the R=0 and R≥2 samples to be drawn from the same
population. This may suggest that BCMs in richer clusters grow more
likely by anisotropic mergers. Our findings support Merritt's model
(1985, ApJ 289, 18) in which most BCMs form during the collapse and
virialization of poor clusters or compact groups with low velocity
dispersions. We show that this model seems to apply to all BCMs, not
only to cD galaxies. This supports the view that most galaxies formed in
groups (and not in rich clusters) with a common dark halo and/or
individual halo of each galaxy which form(s) a local potential minimum
for BCM.
We create a new catalogue of groups and
clusters, applying the
friends-of-friends method to the 2dF GRS final release. We investigate
various selection effects due to the use of a magnitude limited sample.
For this purpose we follow the changes in group sizes and mean galaxy
number densities within groups when shifting nearby observed groups to
larger distances. We study the distribution of sizes of dark matter
haloes in N-body simulations and compare properties of these haloes and
the 2dF groups. We show that at large distances from the observer
luminous and intrinsically greater groups dominate, but in these groups
only very bright members are seen, which form compact cores of the
groups. These two effects almost cancel each other, so that the mean
sizes and densities of groups do not change considerably with distance.
Our final sample contains 10750 groups in the Northern part, and 14465
groups in the Southern part of the 2dF survey with membership N_gal ≥
2. We estimate the total luminosities of our groups, correcting for
group members fainter than the observational limit of the survey. The
cluster catalogue is available at our web-site
(\texttt{http://www.aai.ee/˜maret/2dfgr.html}).
We find groups and clusters of galaxies using
the Data Releases DR1 and
DR3 of the Sloan Digital Sky Survey. We calculate a low-resolution
density field with a smoothing length of 10 h-1 Mpc to
characterise the density of the cluster environment, and a
medium-resolution density field with a smoothing length of 2
h-1 Mpc to characterise the galaxy environment. We determine
the luminosity function of clusters, and investigate properties of
galaxies and clusters in various environments. We show that clusters in
a high-density environment are about 5 times more luminous than in a
low-density environment, and luminosities of galaxies in different
environments differ by a factor of ˜ 25. We see similar effects in
numerical simulations - simulated clusters in a high-density environment
are ~ 100 times more massive than those in a low-density environment.
Comparison of the density distribution in simulations at various epochs
shows that in large low-density regions (voids) dynamical evolution is
very slow and stops early. In contrast, in large regions of higher
density (superclusters) dynamical evolution starts early and continues
until the present; here particles cluster early, and by merging of
smaller groups very rich systems of galaxies form.
From an up-to-date compilation of ACO cluster
redshifts and velocity
dispersions we extract a homogeneous sample of 459 clusters with robust
velocity dispersion. Using the virial theorem to estimate cluster
masses, and a correlation between Abell galaxy counts and R-band
luminosity, we find a median M/LR ≃ 174 h50
Mȯ/Lȯ. However, if we correct the virial
masses according to the X-ray vs. virial mass correlation, as derived
from our analysis, we obtain M/LR ≃ 100 h50
Mȯ/Lȯ. These two values of M/L imply a
mass content of the Universe of Ωm ≃ 0.26 and
0.15, respectively.
The June 2004 version of our compilation of
measured redshifts for
clusters in the Abell-ACO catalogue lists redshifts for 3715
clusters/subclusters in 3033 distinct (2396 A- and 637 S-) clusters, 67
% of these with Nz≥ 3 galaxies measured. We provide
velocity dispersions (σV) for 1875 (sub)clusters
towards 1353 unique ACO clusters. The median σV is 650
km s-1 for A-(sub)clusters and 575 km s-1 for
S-(sub)clusters, and σV clearly increases with both,
Nz and richness, and also, somewhat surprising, with later
Bautz-Morgan type of the clusters. We show examples of supercluster
properties based on these data.
We find clusters and superclusters of galaxies
using the Data Release 1
of the Sloan Digital Sky Survey. We calculate a low-resolution density
field with a smoothing length of 10 h-1100 Mpc to
extract superclusters of galaxies, and a high-resolution density field
with a smoothing length of 0.8 h-1100 Mpc to see
the fine structure within superclusters. We found that clusters in a
high-density environment have luminosities that are about five times
higher than the luminosities of clusters in a low-density environment.
Numerical simulations show that in large underdense regions most
particles form a rarefied population of pregalactic matter whereas in
large overdense regions most particles form a clustered population in
rich clusters. Simulations show also that very massive superclusters are
great attractors and have small bulk motions. Less massive
superclusters are smaller attractors and have much larger bulk motions.
We use a 2-dimensional high-resolution density
field of galaxies of the
Las Campanas Redshift Survey (LCRS) with a smoothing length 0.8
h-1 Mpc to extract clusters and groups of galaxies, and a
low-resolution field with a smoothing length 10 h-1 Mpc to
find superclusters of galaxies. We study the properties of these density
field (DF) clusters and superclusters, and compare the properties of the
DF-clusters and superclusters with those of Abell clusters and
superclusters and LCRS groups. We show that among the cluster samples
studied the DF-cluster sample best describes the large-scale
distribution of matter and the fine structure of superclusters. We
calculate the DF-cluster luminosity function and find that clusters in
high-density environments are about ten times more luminous than those
in low-density environments. We show that the DF-superclusters that
contain Abell clusters are richer and more luminous than the
DF-superclusters without Abell clusters. The distribution of DF-clusters
and superclusters shows the hierarchy of systems in the universe.
We analyze the distribution of Abell clusters
of galaxies to study the
regularity of the supercluster-void network. We apply a new method, the
regularity periodogram, that is sensitive to the geometry of the
location of clusters, and measure the regularity of the network. We find
that the supercluster-void network resembles a cubic lattice over the
entire volume considered (out to the distance of 350 h-1
Mpc). The distribution of clusters in rich superclusters is not
isotropic: it is periodic along a cubic lattice approximately aligned
with the supergalactic coordinates SGX,SGY,SGZ. This large-scale
inhomogeneity does not contradict recent CMB data, but its theoretical
explanation remains a challenge.
We present a comparison of how well the
large-scale structure of the
universe is traced by clusters from the Abell catalog and from the
Automated Plate Measuring Facility (APM). We investigate selection
functions for both cluster catalogs, using samples of all clusters
(including clusters with estimated redshifts) and samples of clusters
with measured redshifts. We present a catalog of superclusters of
galaxies, based on APM clusters up to a redshift zlim=0.13.
We find that the distribution of rich superclusters, defined by all
Abell and APM clusters, is similar in the volume covered by both cluster
samples. We calculate the correlation function for Abell and APM cluster
samples. We show that the supercluster-void network can be traced with
both cluster samples; the network has a period of ~120 h-1
Mpc. However, the APM cluster sample with measured redshifts covers a
small volume, which contains only a few very rich superclusters. These
superclusters surround one void and have exceptionally large mutual
separations. Because of this property, the secondary maximum of the
correlation function of APM clusters with measured velocities is located
at larger scales than the corresponding feature in the correlation
function of Abell clusters. We conclude that the APM sample is not
representative of the large-scale structure as a whole because of the
small volume covered. The Abell cluster catalog is presently the best
sample to investigate the large-scale distribution of high-density
regions in the universe.
We study the spatial distribution of Abell and
X-ray-selected clusters
of galaxies from the ROSAT Bright Source Catalog and determine
correlation functions for both cluster samples. We find that on small
scales the correlation functions depend on the cluster environment:
clusters in rich superclusters have a larger correlation length and
amplitude than clusters of the whole sample. On large scales the
correlation functions depend on the distribution of superclusters, but
for both X-ray and Abell clusters they are oscillating with a period of
~115 h-1 Mpc, indicating the presence of a local peak in the
power spectrum at an effective wavenumber k=0.055 h Mpc-1.
We study the distribution of Abell and
X-ray-selected clusters of
galaxies and derive selection functions of these cluster samples. We
find that selection functions and percolation properties of Abell
clusters of richness class R=0 and R>=1 are similar; the percolation
of X-ray clusters occurs at the same dimensionless radius as the
percolation of Abell clusters. We present a new catalog of superclusters
of Abell clusters out to a redshift of zlim=0.13, a catalog
of X-ray clusters located in superclusters determined by Abell clusters,
and a list of additional superclusters of X-ray clusters. We investigate
the distribution of X-ray-selected clusters of galaxies with respect to
superclusters determined by Abell clusters of galaxies and show that the
distribution of X-ray clusters follows the supercluster-void network
determined by Abell clusters. We find that X-ray clusters are more
strongly clustered than other clusters: the fraction of X-ray clusters
is higher in rich superclusters, and the fraction of isolated X-ray
clusters is lower than the fraction of isolated Abell clusters. Poor,
non-Abell X-ray clusters follow the supercluster-void network as well:
these clusters are embedded in superclusters determined by Abell
clusters and populate filaments between them.
We present a study of the shape, size, and
spatial orientation of
superclusters of galaxies. Approximating superclusters by triaxial
ellipsoids we show that superclusters are flattened, triaxial objects.
We find that there are no spherical superclusters. The sizes of
superclusters grow with their richness: the median semi-major axis of
rich and poor superclusters (having >=8 and <8 member clusters) is
42 and 31h-1Mpc, respectively. Similarly, the median
semi-minor axis is 12 and 5h-1Mpc for rich and poor
superclusters. The spatial orientation of superclusters, as determined
from the axes of the ellipsoids, is nearly random. We do not detect any
preferable orientation of superclusters, neither with respect to the
line of sight, nor relative to some other outstanding feature in the
large scale structure, nor with respect to the directions of principal
axes of adjacent superclusters. (1 data file).
We compare the observed power spectrum of
matter found in our earlier
papers with analytical power spectra. We extrapolate the observed power
spectra on small scales to find the linear power spectrum of matter. We
consider spatially flat cold and mixed dark matter models with the
cosmological constant as well as open models. We fix the Hubble constant
and the baryon density in the middle of the allowed range and vary the
density parameter and the cosmological constant. We determine the
primordial power spectrum of matter using the power spectrum of matter
and the transfer functions of analytical models. We take two different
spectra suggested by observations: one with a sharp maximum at 120 h^-1
Mpc and a second one with a broader maximum, as found for regions with
rich and medium-rich superclusters of galaxies, respectively. For both
models, the primordial power spectra have a break in amplitude; in the
case of the spectrum with a sharp maximum the break is sharp. We
conclude that a scale-free primordial power spectrum is excluded if
presently available data on the distribution of clusters and galaxies
represent the true mass distribution of the universe.
We suggest a new method to determine the bias
parameter of galaxies
relative to matter. The method is based on the assumption that gravity
is the dominating force which determines the formation of the structure
in the universe. Because of gravitational instability, matter flows out
of underdense regions toward overdense regions. To form a galaxy, the
density of matter within a certain radius must exceed a critical value
(Press-Schechter limit) thus galaxy formation is a threshold process. In
low-density environments (voids) galaxies do not form and matter remains
in primordial form. We estimate the value of the threshold density which
divides the matter into two populations, a low-density population in
voids and a clustered population in high-density regions. We investigate
the influence of the presence of these two populations on the power
spectrum of matter and galaxies. We find that the power spectrum of
clustered particles (galaxies) is similar to the power spectrum of
matter. We show that the fraction of total matter in the clustered
population determines the difference between amplitudes of fluctuations
of matter and galaxies, i.e., the bias factor. To determine the fraction
of matter in voids and clustered population we perform numerical
simulations. The fraction of matter in galaxies at the present epoch is
found using a calibration through the sigma_8 parameter. We find
sigma_8=0.89+/-0.09 for galaxies, sigma_8=0.68+/-0.09 for matter, and
b_gal=1.3+/-0.13, the biasing factor of the clustered matter (galaxies)
relative to all matter.
We calculate the mean power spectrum of all
galaxies using published
power spectra of galaxies and clusters of galaxies. On small scales we
use the power spectrum derived from the two-dimensional distribution of
Automatic Plate Measuring Facility (APM) galaxies, since this sample is
not influenced by redshift distortions and is the largest and deepest
sample of galaxies available. On large scales we use power spectra
derived from three-dimensional data for various galaxy and cluster
samples which are reduced to real space and in amplitude to the power
spectrum of APM galaxies. We find that available data indicate the
presence of two different populations in the nearby universe. Clusters
of galaxies sample a relatively large region in the universe where rich,
medium, and poor superclusters are well represented. Their mean power
spectrum has a spike at wavenumber k=0.05+/-0.01 h Mpc^-1, followed by
an approximate power-law spectrum of index n~-1.9 toward small scales.
Some galaxy surveys (APM three-dimensional, IRAS QDOT, and SSRS+CfA2 130
Mpc) have similar spectra. The power spectrum found from the Las
Campanas Redshift Survey and IRAS 1.2 Jy surveys is flatter around the
maximum, which may represent regions of the universe with medium-rich
and poor superclusters. Differences in power spectra for these
populations may partly be due to the survey geometries of the data sets
in question and/or to features of the original data analysis.
We present a study of the shape, size, and
spatial orientation of
superclusters of galaxies. Approximating superclusters by triaxial
ellipsoids we show that superclusters are flattened, triaxial objects.
We find that there are no spherical superclusters. The sizes of
superclusters grow with their richness: the median semi-major axis of
rich and poor superclusters (having >=8 and <8 member clusters) is
42 and 31 h(-1) Mpc, respectively. Similarly, the median semi-minor axis
is 12 and 5 h(-1) Mpc for rich and poor superclusters. The spatial
orientation of superclusters, as determined from the axes of ellipsoids,
is nearly random. We do not detect any preferable orientation of
superclusters, neither with respect to the line of sight, nor relative
to some other outstanding feature in the large scale structure, nor with
respect to the directions of principal axes of adjacent superclusters.
We investigate the distribution of Abell-ACO
clusters of galaxies, and
show that clusters of galaxies located in rich superclusters form a
quasiregular network with step size 120~\Mpc. The power spectrum of
clusters of galaxies has a sharp peak at a wavelength equal to the step
size of the network, the correlation function of clusters is oscillating
with this period.
We present an update of our compilation of
measured redshifts of galaxy
clusters in the all-sky Abell catalog. In the last 7 years the number of
ACO clusters with measured redshift has doubled to now ~2100, but still
about 56 percent of these are based on only 1 or 2 measured member
galaxies. Our October 1997 version gives 2247 redshifts (including
components or line-of-sight superpositions) for 2114 distinct A- and
S-clusters. Velocity dispersions are listed for 536 different ACO
clusters (613 subclusters) and the median is 695 km/s. We mention some
applications of our compilation for determining the large-scale
structure of the nearby Universe.
We use rich clusters of galaxies in the
Northern and Southern Galactic
hemispheres up to a redshift z=0.12 to determine the cluster correlation
function for a separation interval ~650h^-1 Mpc (h is the Hubble
constant in units of 100 kms^-1Mpc^-1). We show that superclusters of
galaxies and voids between them form a moderately regular network. As a
result the correlation function determined for clusters located in rich
superclusters oscillates: it has a series of regularly spaced secondary
maxima and minima. The scale of the supercluster-void network,
determined from the period of oscillations, is P=115+/-15h^-1 Mpc. Five
periods are observed. The correlation function found for clusters in
poor and medium-rich superclusters is zero on large scales. The
correlation functions calculated separately for the Northern and
Southern Galactic hemispheres are similar; only the amplitude of
oscillations for clusters in the Southern hemisphere is larger by a
factor of about 1.5. We investigate the influence of possible errors in
the correlation function. The amplitude of oscillations for clusters in
very rich superclusters is about 3 times larger than the estimated
error. We argue that the oscillations in the correlation function are
due neither to the double-cone shape of the observed volume of space,
nor to the inaccuracy in the selection function. We compare the observed
cluster correlation function with similar functions derived for popular
models of structure formation, as well as for simple geometrical models
of cluster distribution. We find that the production of the observed
cluster correlation function in any model with a smooth transition of
the power spectrum from a Harrison-Zeldovich regime with positive
spectral index at long wavelengths to a negative spectral index at short
wavelengths is highly unlikely. The power spectrum must have an extra
peak located at a wavelength equal to the period of oscillations of the
correlation function. The relative amplitude of the peak over the smooth
spectrum is probably of the order of a factor of at least 1.25. These
quantitative tests show that high-density regions in the Universe marked
by rich clusters of galaxies are distributed more regularly than
expected. Thus our present understanding of structure formation needs
revision.
Since the appearance of ACO's all-sky cluster
catalog in 1989 (with 822
redshifts) no redshift compilation of the full sample appeared in print.
We present an update of a compilation of measured redshifts for both A-
and S-clusters we maintain since 1989 [1991ASPC...15..279A;
1995ApL&C..31...27A]. Different from most previous compilations, we
systematically scan the literature for any galaxy redshifts in the
direction of ACO clusters. Apart from compilations like ``ZCAT'' and
``SRC'', recent redshift surveys like the LCRS and APM bright galaxy
surveys proved to be rich in ACO cluster redshifts, though these
associations have not been reported in literature. We include redshifts
within a factor of 4 of the currently best photometric estimate
zest [1992MNRAS.259..494P], flagging those deviating by a
factor of >2. Over the past 8 years the number of ACO clusters with
measured redshifts has more than doubled. Our May 1997 version gives
2190 entries for 2063 distinct ACO clusters (1665 A- and 398
S-clusters), including subclusters or line-of-sight superpositions. Of
these entries ˜2100 entries (for ˜2000 different ACO names)
are within a factor 2 from zest. In Fig. 1 the number of
clusters (Ncl) with redshifts for at least Nz
member galaxies is plotted vs. Nz, for the ``SR91''
[1991ApJS...77..363S] compilation of northern ACO clusters, as well as
for our previous [1995ApL&C..31...27A] and present full-sky
compilations. Note that since SR91 [1991ApJS...77..363S] the fraction
of clusters with ``reliable'' redshifts (i.e. Nz ≥ 3) has
risen from ˜32% to no more than ˜45% now. There are
˜90 clusters with Nz>50, the typical minimum for
dynamical studies. The total number of galaxies involved is 20,900,
(10,700 for A-, 6900 for ACO-, and 3300 for S-clusters), neglecting some
overlap for a few clusters. Whenever individual redshifts are available
for N≥5 galaxies, we combine various sources and calculate a velocity
dispersion σV. We quote σV for 517
different ACO clusters (590 subclusters). Their median is 690 km/s (Fig.
2). Our compilation (now based on 335 references) includes: Abell and
subcomponent name (if any); an IAU-type position of the center including
some updates since ACO89; R, D, and BM classes; mean z wrt the Local
Group; a flag indicating the consistency between zobs and
zest; Nz; references; σV, plus a
reference and the number of galaxies contributing to
σV, if different from that for z; detailed notes for
nearly 40% of all entries, e.g. on alternative or additional redshifts.
We shall use our data set to derive an improved m10-z
relation, separately for northern, southern and supplementary ACO
clusters, and and iteratively clean our sample from ``discordant''
redshifts. We show some applications on the large-scale structure of the
nearby Universe.
We investigate the distribution of
superclusters and voids using a new
catalogue of superclusters of rich clusters of galaxies which extends up
to a redshift of $z = 0.12$. The new catalogue contains 220
superclusters of rich clusters, of which 90 superclusters have been
determined for the first time. Among them there are several very rich
superclusters, containing at least eight member clusters. We demonstrate
that two thirds of very rich superclusters are concentrated to a
Dominant Supercluster Plane which is situated at a right angle with
respect to the plane of the Local Supercluster and adjacent nearby
superclusters. We apply several methods to estimate the characteristic
distance between superclusters. The results indicate consistently the
presence of a quite regular supercluster-void network with scale of
approx 120 Mpc. Comparison with random supercluster catalogues shows
significant differences between spatial distributions of real and random
superclusters. We determine the selection function of the sample of
clusters and suggest that the mean true space density of Abell clusters
is 2.6 x 10^{-5} h^3 Mpc^{-3}, twice the conventionally used value.
Table A2 is only available in electronic form at the Centre des Donnees
astronomiques Strasbourg via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html}.
ACCORDING to the favoured models for the
formation of large-scale
structure in the Universe (in which the dynamics of the Universe is
dominated by cold dark matter), the distribution of galaxies and
clusters of galaxies should be random on large scales. It therefore came
as a surprise when a periodicity was reported1 in the
distribution of high-density regions of galaxies in the directions of
the Galactic poles, although the apparent lack of periodicity in other
directions led to the initial report being regarded as a statistical
anomaly2. A subsequent study3-6 also claimed
evidence for periodicity on the same scale, but the statistical
significance of this result was uncertain due to the small number of
clusters used. Here, using a new compilation7 of available
data on galaxy clusters, we present evidence for a quasi-regular
three-dimensional network of rich superclusters and voids, with the
regions of high density separated by ~120 Mpc. If this reflects the
distribution of all matter (luminous and dark), then there must exist
some hitherto unknown process that produces regular structure on large
scales.
We study the whole-sky distribution of rich
clusters of galaxies up to
the distance z~0.1 and present catalogues of superclusters and
cluster-defined voids. The data on clusters, superclusters and voids
show the presence of the characteristic scale of 130h-1Mpc in
the supercluster-void network, found earlier by Broadhurst et al.
(1990Natur.343..726B) from a one-dimensional study. This scale has been
detected in the distribution of clusters of richnesses R=0 and R>=1.
We perform tests to study the influence of projection effects. The
clusters that do not belong to superclusters are located in the vicinity
of superclusters and form their outlying parts. We compare the
distribution of ACO clusters with that of APM clusters. The APM clusters
determine a smaller scale: 100h-1Mpc. We discuss the possible
reasons for this difference. (3 data files).
We use a compilation of redshifts of rich
clusters by Andernach, Tago
and Stengler-Larrea (1996, in preparation) to determine superclusters of
rich clusters up to a redshift of z=0.12. Superclusters were searched
for with a clustering algorithm, using a neighbourhood radius of
24h-1Mpc (h is the Hubble constant in units of 100km/s/Mpc).
The catalogue contains 220 superclusters of rich clusters, of which 90
superclusters have been determined for the first time. Table A2 gives
the supercluster number, its multiplicity, centre coordinates, a list of
member clusters and identifications with the catalogue by Einasto et al.
(1994MNRAS.269..301E).
(1 data file).
Supervoids are regions in the local Universe
which do not contain rich
clusters of galaxies. In order to investigate the distribution of
galaxies in and around supervoids, we have studied the closest example,
the Northern Local Void. It is defined as the region between the Local,
Coma, and the Hercules superclusters, which is well covered by available
redshift surveys. We find that this supervoid is not empty, but it
contains small galaxy systems and poor clusters of galaxies. We study
the cosmography of this void by analyzing the distribution of poor
clusters of galaxies, elliptical and other galaxies in two projections.
We present a catalogue of voids, defined by galaxies of different
morphological type and luminosity, and analyze mean diameters of voids
in different environments. This analysis shows that sizes of voids and
properties of void walls are related. Voids defined by poor clusters of
galaxies and by bright elliptical galaxies have a mean diameter of up to
40h^-1^Mpc. Faint late-type galaxies divide these voids into smaller
voids. The faintest galaxies we can study are outlining voids with mean
diameters of about 8h^-1^Mpc. Voids located in a high-density
environment are smaller than voids in low-density regions. The
dependence of void diameters on the type and luminosity of galaxies, as
well as on the large-scale environment shows that voids form a
hierarchical system.
We have developed a parameter-independent
method to detect local maxima
of the two-point correlation function. By applying it to two samples of
rich Abell clusters of galaxies with redshift limits z<0.08 and
z<0.12 we detect three maxima centered at 150 Mpc, 300 Mpc and 430
Mpc with confidence levels 80% and higher. This sequence of fluctuations
has an average interval of 140 Mpc, that can be explained by a power
spectrum with a distinct peak at k=0.048+-0.005/Mpc.
We describe the present status of our
compilation of measured redshifts
for both A- and S-clusters of galaxies from Abell, Corwin & Olowin
(ACO). Over the past five years the number of ACO clusters with measured
redshifts increased from ~1000 to ~1650. However, the fraction of
clusters with at least 3 member redshifts remained at ~30 percent. A
velocity dispersion is known for ~330 ACO clusters. The median
dispersion is 760 km/s and a histogram of their distribution is
presented.
We study the whole-sky distribution of rich
clusters of galaxies up to
the distance z ~ 0.1 and present catalogues of superclusters and
cluster- defined voids. The data on clusters, superclusters and voids
show the presence of the characteristic scale of 130 h^-1^ Mpc in the
supercluster-void network, found earlier by Broadhurst et al. from a
one- dimensional study. This scale has been detected in the distribution
of clusters of richnesses R = 0 and R >= 1. We perform tests to study
the influence of projection effects. The clusters that do not belong to
superclusters are located in the vicinity of superclusters and form
their outlying parts. We compare the distribution of ACO clusters with
that of APM clusters. The APM clusters determine a smaller scale: 100
h^-1^ Mpc. We discuss the possible reasons for this difference.
The authors study the whole-sky distribution
of Abell clusters of
galaxies up to distance z ≍ 0.1. The distribution of clusters,
superclusters and voids show the presence of the characteristic scale of
130 h-1Mpc in the supercluster-void network, found earlier by
Broadhurst et al. (1990) from 1-dimensional study. This scale is
detected in the distribution of Abell clusters of richness both R = 0
and R ≥ 1. The authors compare the distribution of ACO clusters with
that of APM clusters. The APM clusters determine a smaller scale - 100
h-1Mpc. The authors discuss the possible reasons of this
difference.
The power spectrum of the distribution of
clusters of galaxies in the
northern and southern galactic hemispheres has been evaluated.
Corrections have been applied for the smoothing effect, and for the
Poisson noise. The effects of incompleteness of data and observational
errors have been investigated. The cluster spectrum has been transformed
to galaxy and matter power spectra. Data suggest that the power spectrum
has an index in the range of -2 and -1 on intermediate scales; on very
large scales the spectrum is consistent with the Harrison-Zeldovich
index n = 1. The transition from the Harrison-Zeldovich index to a lower
index occurs at the scale lambda(t) is approximately equal to 150 +/-
50/h Mpc. Direct comparison of the samples used and power-spectrum
analysis suggest that our samples approach the size of fair samples of
the universe.
In this paper we study the density spectrum of
the distribution of
galaxies and clusters of galaxies in the 'nearby' universe: What does it
tell us about the distribution and evolution of matter in the universe?
Spatial distribution of galaxies and the
Zwicky clusters of galaxies in
the nearby Universe has been studied. Correlation function, cluster
analysis, percolation analysis and other methods have been applied. Both
qualitative analyses and statistical tests support rather filamentary or
sponge-like than bubble-like structure of the distribution of galaxies.
The spatial distribution of galaxies and
Zwicky clusters of galaxies in
the Coma Supercluster and its large-scale environment are studied.
Quantitative analyses and statistical tests demonstrate a non-random
clustering and the existence of filamentary structures in the
distribution of clusters and galaxies.
Some statistical tests have been used for the
study of the spatial
distribution of near Zwicky clusters of galaxies in the Coma
Supercluster and its large-scale environment. The nearest neighbourhood
test and the multiplicity and percolation analyses demonstrate the
non-random clustering and the filamentary structure of the distribution
of clusters.
The two-point three-dimensional correlation
function of nearby Zwicky
clusters is obtained for a large region of the northern galactic
hemisphere (alpha in the range of 9-15 h, delta greater than or equal to
zero, and V(0) in the 2000-9000 km/s range). With allowance for galactic
absorption and redshift selection, it is found that the correlation
function of the Zwicky clusters is similar to the correlation function
of galaxies when r is less than 25 Mpc. However, it shows excess
clustering when r is in the range of 25-70 Mpc.
Distances have been derived for Zwicky "near"
clusters of galaxies,
located at 9h < R.A. > 15h, and Decl. >
-3°, by using Huchra's compilation of galaxy redshifts, original
redshift observations and photometric distance indicators.
An outstanding string of galaxies and of small
groups in Bootes has been
found during a study of bridges between the Coma and the Local
superclusters. It lies on the boundary of a large void between the
Hercules and the Local superclusters, has a length of 50 Mpc, is only a
few megaparsecs wide and consists of non-elliptical galaxies. A possible
explanation by a specific Langrangian singularity at the formation, the
imprint of which has survived in the present galaxy distribution, is
proposed.
The Coma-A1367 Supercluster and its
large-scale environment are
investigated. The Zwicky et al. (1961-68) clusters are used as
supercluster tracers; superclusters are defined not by visual impression
but on the basis of cluster analysis. Attention is restricted to an area
of the sky where RA is between 9h and 15h, with Dec. greater than -3
deg. Clustering analysis is applied to study the spatial distribution.
At neighborhood radii R = 15-25 Mpc (for Hubble constant H = 50 km per s
per Mpc), the clusters form chains and superclusters of galaxies. It is
noted that at R = 26-28 Mpc, superclusters merge to a single connected
network. Cluster chains link the Coma-A1367 Supercluster with the Local
Supercluster, A779, and Hercules Superclusters. The Coma-A1367
Supercluster comprises four cluster chains, and its diameter is greater
than 100 Mpc. It is noted that a typical cluster chain has eight Zwicky
clusters and is 80 Mpc in length. Most, if not all, of the clusters form
connected systems. Empty regions devoid of clusters have diameters up to
100 Mpc in this region of the sky. The morphology distribution of bright
galaxies and the mean absolute magnitude of first ranked galaxies in
Zwicky clusters are found to be similar to the respective quantities in
Abell clusters.
Joeveer, M.: Spatial distribution of galaxies
and of clusters of galaxies in the southern galactic hemisphere
