259 research outputs found

### Cosmology with Clusters of Galaxies

I show that three independent methods utilizing clusters of galaxies -
cluster dynamics and mass-to-light ratio, baryon fraction in clusters, and
cluster evolution - all indicate the same robust result: the mass-density of
the universe is low, Omega ~ 0.2, and the mass approximately traces light on
large scales.Comment: Invited talk at Nobel98, ``Particle Physics and the
Universe,''8/1998, 15 pages, 4 figure

### CLUSTERING AND LARGE SCALE STRUCTURE WITH THE SDSS

The Sloan Digital Sky Survey (SDSS) will provide a complete imaging and
spectroscopic survey of the high-latitude northern sky. The 2D survey will
image the sky in five colors and will contain nearly 5 x 107 galaxies to g ~
23m. The spectroscopic survey will obtain spectra of the brightest 106
galaxies, 105 quasars, and 103.5 rich clusters of galaxies (to g~18.3-19.3m,
respectively). I summarize some of the science opportunities that will be made
possible by this survey for studying the clustering and large-scale structure
of the universe.
The survey will identify a complete sample of several thousand rich clusters
of galaxies, both in 2D and 3D - the largest automated sample yet available.
The extensive cluster sample can be used to determine critical clustering
properties such as the luminosity-function, velocity-function, and
mass-function of clusters of galaxies (a critical test for cosmological
models), detailed cluster dynamics and W(dyn), the cluster correlation function
and its dependence on richness, cluster evolution, superclustering and voids to
the largest scales yet observed, the motions of clusters and their large-scale
peculiar velocity field, as well as detailed correlations between x-ray and
optical properties of clusters, the density-morphology relation, and
cluster-quasar associations. The large redshift survey, reaching to a depth of
600h-1 Mpc, will accurately map the largest scales yet observed, determine the
power-spectrum and correlation function on these large scales for different
type galaxies, and study the clustering of quasars to high redshifts (z 4). The
implications of the survey for cosmological models, the dark matter, and W are
also discussed.Comment: compressed PostScript, invited talk presented at the AAS meeting,
Minneapolis, June 1994, to appear in PASP 1995; for the figures contact
[email protected]

### Present Status of the Theoretical Predictions for the ^(37)Cl Solar-Neutrino Experiment

The theoretical predictions for the ^(37)Cl solar-neutrino experiment are summarized and compared with the experimental results of Davis, Harmer, and Hoffman. Three important conclusions about the sun are shown to follow

### COSMOLOGY WITH CLUSTERS OF GALAXIES

Rich clusters of galaxies, the largest virialized systems known, provide a
powerful tool for the study of cosmology. Some of the fundamental questions
that can be addressed with clusters of galaxies include: how did galaxies and
large-scale structure form and evolve? What is the amount, composition and
distribution of matter in the universe? I review some of the studies utilizing
clusters of galaxies to investigare, among others:
- The dark matter on clusters scale and the mean mass-density of the
universe;
- The large-scale structure of the universe;
- The peculiar velocity field on large scales;
- The mass-function of groups and clusters of galaxies;
- The constraints placed on specific cosmological models using the cluster
data.Comment: compressed PostScript, to appear in the Proceedings of 11th Potsdam
Cosmology Workshop on "Large Scale Structrure in the Universe", 1994; for the
figures contact [email protected]

### 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]

### 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 ($\Omega=1$)
CDM, low-density CDM, HDM ($\Omega=1$), 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 $v \sim 500$ km s$^{-1}$, and extends to high cluster velocities of $v \sim
1500$ km s$^{-1}$. Approximately 10\% of all model rich clusters move with high
peculiar velocities of $v \ge 10^3$ km s$^{-1}$. 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 $v_r \sim 3000$ km s$^{-1}$. 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

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