30 research outputs found
Primordial Feature at the Scale of Superclusters of Galaxies
We investigate a spatially-flat cold dark matter model (with the matter
density parameter ) with a primordial feature in the initial
power spectrum. We assume that there is a bump in the power spectrum of density
fluctuations at wavelengths Mpc, which correspond to
the scale of superclusters of galaxies. There are indications for such a
feature in the power spectra derived from redshift surveys and also in the
power spectra derived from peculiar velocities of galaxies. We study the mass
function of clusters of galaxies, the power spectrum of the CMB temperature
fluctuations, the rms bulk velocity and the rms peculiar velocity of clusters
of galaxies. The baryon density is assumed to be consistent with the BBN value.
We show that with an appropriately chosen feature in the power spectrum of
density fluctuations at the scale of superclusters, the mass function of
clusters, the CMB power spectrum and peculiar velocities are in good agreement
with the observed data.Comment: 8 pages, 6 figures, with final revisions, MNRAS in press, new CMB
data adde
The Motions of Clusters and Groups of Galaxies
The distributions of peculiar velocities of rich clusters and of groups of
galaxies are investigated for different cosmological models and are compared
with observations. Four cosmological models are studied: standard ()
CDM, low-density CDM, HDM (), and PBI. We find that rich clusters of
galaxies exhibit a Maxwellian distribution of peculiar velocities in all
models, as expected from a Gaussian initial density fluctuation field. The
cluster 3-D velocity distribution is generally similar in the models: it peaks
at km s, and extends to high cluster velocities of km s. Approximately 10\% of all model rich clusters move with high
peculiar velocities of km s. The highest velocity clusters
frequently originate in dense superclusters. The group velocity distribution
is, in general, similar to the velocity distribution of the rich clusters. In
all but the low-density CDM model, the mass exhibits a longer tail of high
velocities than do the clusters. This high-velocity tail originates mostly from
the high velocities that exist within rich clusters. The model velocity
distributions of groups and clusters of galaxies are compared with
observations. The data are generally consistent with the models, but exhibit a
somewhat larger high-velocity tail, to km s. While this
high-velocity tail is similar to the HDM model predictions, the data are
consistent with the other models studied, including the low-density CDM model,
which best fits most other large-scale structure observations. The observed
velocityComment: 25p plaintex submitted to The Astrophysical Journa
Velocity Correlations of Galaxy Clusters
We determine the velocity correlation function, pairwise peculiar velocity
difference, and root-mean-square pairwise peculiar velocity dispersion of rich
clusters of galaxies, as a function of pair separation, for three cosmological
models: Omega=1 and Omega=0.3 CDM, and Omega=0.3 PBI models (all flat and
COBE-normalized). We find that close cluster pairs, with separation r<10Mpc/h,
exhibit strong attractive peculiar velocities in all models; the cluster
pairwise velocities depend sensitively on the model. The mean pairwise
attractive velocity of clusters on 5Mpc/h scale ranges from 1700 km/s for
Omega=1 CDM, to 1000 km/s for PBI, to 700 km/s for Omega=0.3 CDM. The
small-scale pairwise velocities depend also on cluster mass: richer, more
massive clusters exhibit stronger attractive velocities than less massive
clusters. On large scales, from 20 to 200Mpc/h, the cluster peculiar velocities
are increasingly dominated by bulk and random motions; they are independent of
cluster mass. The cluster velocity correlation function, which reflects the
bulk motion minus the relative motion of pairs, is negative on small scales for
Omega=1 and Omega=0.3 CDM, and positive for PBI; this indicates stronger
pairwise motion than bulk motion on small scales for CDM, and relatively larger
bulk motions for PBI. The cluster velocity correlation function is positive on
very large scales, from 10 to 200Mpc/h, for all models. These positive
correlations, which decrease monotonically with scale, indicate significant
bulk motions of clusters up to 200Mpc/h. The strong dependence of the cluster
velocity functions on models, especially at small separations, makes them
useful tools in constraining cosmological models when compared with
observations.Comment: 12p postscript file, in press of The Astrophysical Journal Letters
Local report# 94915,email: [email protected]
Probing the Large-Scale Velocity Field with Clusters of Galaxies
What is the role of clusters of galaxies in probing the large-scale velocity
field of the universe? We investigate the distribution of peculiar velocities
of clusters of galaxies in the popular low-density () flat
Cold-Dark-Matter (CDM) cosmological model, which best fits many large-scale
structure observations. An CDM model is also studied for comparison.
We find that clusters of galaxies are efficient tracers of the large-scale
velocity field. The clusters exhibit a Maxwellian distribution of peculiar
velocities, as expected from Gaussian initial density fluctuations. The cluster
3-D velocity distribution for the model peaks at km
s, and extends to high velocities of km s. The rms
peculiar velocity of the clusters is km s. Approximately 10\% of
all model clusters move with high peculiar velocities of km
s. The observed velocity distribution of clusters of galaxies is
compared with the predictions from cosmological models. The observed data
exhibit a larger velocity tail than seen in the model simulations; however, due
to the large observational uncertainties, the data are consistent at a level with the model predictions, and with a Gaussian initial density
field. The large peculiar velocities reported for some clusters of galaxies ( km s) are likely to be overestimated, if the current model is
viable.Comment: 14 plaintex pages, to appear in the Astrophysical Journal Letters,
local report CE
Unusual A2142 supercluster with a collapsing core: distribution of light and mass
We study the distribution, masses, and dynamical properties of galaxy groups
in the A2142 supercluster. We analyse the global luminosity density
distribution in the supercluster and divide the supercluster into the
high-density core and the low-density outskirts regions. We find galaxy groups
and filaments in the regions of different global density, calculate their
masses and mass-to-light ratios and analyse their dynamical state with several
1D and 3D statistics. We use the spherical collapse model to study the
dynamical state of the supercluster. We show that in A2142 supercluster groups
and clusters with at least ten member galaxies lie along an almost straight
line forming a 50 Mpc/h long main body of the supercluster. The A2142
supercluster has a very high density core surrounded by lower-density outskirt
regions. The total estimated mass of the supercluster is M_est = 6.2
10^{15}M_sun. More than a half of groups with at least ten member galaxies in
the supercluster lie in the high-density core of the supercluster, centered at
the rich X-ray cluster A2142. Most of the galaxy groups in the core region are
multimodal. In the outskirts of the supercluster, the number of groups is
larger than in the core, and groups are poorer. The orientation of the cluster
A2142 axis follows the orientations of its X-ray substructures and radio halo,
and is aligned along the supercluster axis. The high-density core of the
supercluster with the global density D8 > 17 and perhaps with D8 > 13 may have
reached the turnaround radius and started to collapse. A2142 supercluster with
luminous, collapsing core and straight body is an unusual object among galaxy
superclusters. In the course of the future evolution the supercluster may be
split into several separate systems.Comment: 13 pages, 9 figures, Astronomy and Astrophysics, in press. References
update
Infalling groups and galaxy transformations in the cluster A2142
We study galaxy populations and search for possible merging substructures in
the rich galaxy cluster A2142. Normal mixture modelling revealed in A2142
several infalling galaxy groups and subclusters. The projected phase space
diagram was used to analyse the dynamics of the cluster and study the
distribution of various galaxy populations in the cluster and subclusters. The
cluster, supercluster, BCGs, and one infalling subcluster are aligned. Their
orientation is correlated with the alignment of the radio and X-ray haloes of
the cluster. Galaxies in the centre of the main cluster at the clustercentric
distances have older stellar populations (with the median age
of ~Gyrs) than galaxies at larger clustercentric distances.
Star-forming and recently quenched galaxies are located mostly in the infall
region at the clustercentric distances ,
where the median age of stellar populations of galaxies is about ~Gyrs.
Galaxies in A2142 have higher stellar masses, lower star formation rates, and
redder colours than galaxies in other rich groups. The total mass in infalling
groups and subclusters is ,
approximately half of the mass of the cluster, sufficient for the mass growth
of the cluster from redshift (half-mass epoch) to the present. The
cluster A2142 may have formed as a result of past and present mergers and
infallen groups, predominantly along the supercluster axis. Mergers cause
complex radio and X-ray structure of the cluster and affect the properties of
galaxies in the cluster, especially in the infall region. Explaining the
differences between galaxy populations, mass, and richness of A2142, and other
groups and clusters may lead to better insight about the formation and
evolution of rich galaxy clusters.Comment: 16 pages, 13 figures, A&A, in pres
BOSS Great Wall: morphology, luminosity, and mass
We study the morphology, luminosity and mass of the superclusters from the
BOSS Great Wall (BGW), a recently discovered very rich supercluster complex at
the redshift . We have employed the Minkowski functionals to quantify
supercluster morphology. We calculate supercluster luminosities and masses
using two methods. Firstly, we used data about the luminosities and stellar
masses of high stellar mass galaxies with .
Secondly, we applied a scaling relation that combines morphological and
physical parameters of superclusters to obtain supercluster luminosities, and
obtained supercluster masses using the mass-to-light ratios found for local
rich superclusters. We find that the BGW superclusters are very elongated
systems, with shape parameter values of less than . This value is lower
than that found for the most elongated local superclusters. The values of the
fourth Minkowski functional for the richer BGW superclusters (
and ) show that they have a complicated and rich inner structure. We
identify two Planck SZ clusters in the BGW superclusters, one in the richest
BGW supercluster, and another in one of the poor BGW superclusters. The
luminosities of the BGW superclusters are in the range of , and masses in the range of . Supercluster luminosities and masses obtained
with two methods agree well. We conclude that the BGW is a complex of massive,
luminous and large superclusters with very elongated shape. The search and
detailed study, including the morphology analysis of the richest superclusters
and their complexes from observations and simulations can help us to understand
formation and evolution of the cosmic web.Comment: Comments: 10 pages, 2 figures, A&A, in pres