16 research outputs found
Acoustic Oscillations in the Early Universe and Today
During its first ~100,000 years, the universe was a fully ionized plasma with
a tight coupling by Thompson scattering between the photons and matter. The
trade--off between gravitational collapse and photon pressure causes acoustic
oscillations in this primordial fluid. These oscillations will leave
predictable imprints in the spectra of the cosmic microwave background and the
present day matter-density distribution. Recently, the BOOMERANG and MAXIMA
teams announced the detection of these acoustic oscillations in the cosmic
microwave background (observed at redshift ~1000). Here, we compare these CMB
detections with the corresponding acoustic oscillations in the matter-density
power spectrum (observed at redshift ~0.1). These consistent results, from two
different cosmological epochs, provide further support for our standard Hot Big
Bang model of the universe.Comment: To appear in the journal Science. 6 pages, 1 color figur
Possible Detection of Baryonic Fluctuations in the Large-Scale Structure Power Spectrum
We present a joint analysis of the power spectra of density fluctuations from
three independent cosmological redshift surveys; the PSCz galaxy catalog, the
APM galaxy cluster catalog and the Abell/ACO cluster catalog. Over the range
0.03 <= k <= 0.15 h/Mpc,the amplitudes of these three power spectra are related
through a simple linear biasing model with b = 1.5 and b = 3.6 for Abell/ACO
versus APM and Abell/ACO versus the PSCz respectively. Furthermore, the shape
of these power spectra are remarkably similar despite the fact that they are
comprised of significantly different objects (individual galaxies through to
rich clusters). Individually, each of these surveys show visible evidence for
``valleys'' in their power spectra. We use a newly developed statistical
technique called the False Discovery Rate, to show that these ``valleys'' are
statistically significant. One favored cosmological explanation for such
features in the power spectrum is the presence of a non-negligible baryon
fraction (Omega_b/Omega_m) in the Universe which causes acoustic oscillations
in the transfer function of adiabatic inflationary models. We have performed a
maximum-likelihood marginalization over four important cosmological parameters
of this model (Omega_m, Omega_b, n_s, H_o). We use a prior on H_0 = 69(+/-15),
and find Omega_mh^2 = 0.12(+0.03/-0.02), Omega_bh^2 =0.029(+0.011/-0.015), n_s
= 1.08^(+0.17/-0.20) (2 sigma confidence limits) which are fully consistent
with the favored values of these cosmological parameters from the recent Cosmic
Microwave Background (CMB) experiments. This agreement strongly suggests that
we have detected baryonic oscillations in the power spectrum of matter at a
level expected from a Cold Dark Matter model normalized to fit these CMB
measurements.Comment: 13 pages, 4 figures, ApJ in press. Typos fixed. Replaced Figure 4
with improved versio
ROSAT PSPC Observations of the Richest () ACO Clusters
We have compiled an X-ray catalog of optically selected rich clusters of
galaxies observed by the PSPC during the pointed GO phase of the ROSAT mission.
This paper contains a systematic X-ray analysis of 150 clusters with an optical
richness classification of from the ACO catalog (Abell, Corwin, and
Olowin 1989). All clusters were observed within 45' of the optical axis of the
telescope during pointed PSPC observations. For each cluster, we calculate: the
net 0.5-2.0 keV PSPC count rate (or upper limit) in a 1 Mpc radius
aperture, 0.5-2.0 keV flux and luminosity, bolometric luminosity, and X-ray
centroid. The cluster sample is then used to examine correlations between the
X-ray and optical properties of clusters, derive the X-ray luminosity function
of clusters with different optical classifications, and obtain a quantitative
estimate of contamination (i.e, the fraction of clusters with an optical
richness significantly overestimated due to interloping galaxies) in the ACO
catalog
Multi-Scale Morphological Analysis of SDSS DR5 Survey using the Metric Space Technique
Following novel development and adaptation of the Metric Space Technique
(MST), a multi-scale morphological analysis of the Sloan Digital Sky Survey
(SDSS) Data Release 5 (DR5) was performed. The technique was adapted to perform
a space-scale morphological analysis by filtering the galaxy point
distributions with a smoothing Gaussian function, thus giving quantitative
structural information on all size scales between 5 and 250 Mpc. The analysis
was performed on a dozen slices of a volume of space containing many newly
measured galaxies from the SDSS DR5 survey. Using the MST, observational data
were compared to galaxy samples taken from N-body simulations with current best
estimates of cosmological parameters and from random catalogs. By using the
maximal ranking method among MST output functions we also develop a way to
quantify the overall similarity of the observed samples with the simulated
samples
Cluster Winds Blow along Supercluster Axes
Within Abell galaxy clusters containing Wide-Angle Tailed radio sources, there is evidence of a ``prevailing wind'' which directs the WAT jets. We study the alignment of nine WAT jets and nearby clusters to test the idea that this wind may be a fossil of drainage along large-scale filaments. We also test this idea with a study of the alignment of WAT jets and filament axes. Statistical tests indicate no significant alignment of WAT jets towards nearest neighbour clusters, but a highly significant alignment with the long axis of the supercluster in which the cluster lies
Projection, Spatial Correlations, and Anisotropies in a Large and Complete Sample of Abell Clusters
An analysis of R >= 1 Abell clusters is presented for samples containing
recent redshifts from the MX Northern Abell Cluster Survey. The newly obtained
redshifts from the MX Survey as well as those from the ESO Nearby Abell Cluster
Survey (ENACS) provide the necessary data for the largest magnitude-limited
correlation analysis of rich clusters in the entire sky (excluding the galactic
plane) to date. We find 19.4 <= r_0 <= 23.3 h^-1Mpc, -1.92 <= gamma <= -1.83
for four different subsets of Abell/ACO clusters, including a large sample
(N=104) of cD clusters. We have used this dataset to look for line-of-sight
anisotropies within the Abell/ACO catalogs. We show that the strong
anisotropies present in previously studied Abell cluster datasets are not
present in our R >= 1 samples. There are, however, indications of residual
anisotropies which we show are the result of two elongated superclusters, Ursa
Majoris and Corona Borealis, whose axes lie near the line-of-sight. After
rotating these superclusters so that their semi-major axes are prependicular to
the line-of-sight, we find no anisotropies as indicated by the correlation
function. The amplitude and slope of the two-point correlation function remain
the same before and after these rotations. We also remove a subset of R = 1
Abell/ACO clusters that show sizable foreground/background galaxy contamination
and again find no change in the amplitude or slope of the correlation function.
We conclude that the correlation length of R >= 1 Abell clusters is not
artificially enhanced by line-of-sight anisotropies.Comment: 37 pages, 8 figures, AASTeX Accepted for publication in Ap
Three-Dimensional Filamentation Analysis of SDSS DR5 Survey
We introduce a new method to calculate the multi-scale 3D filamentation of
SDSS DR5 galaxy clusters and also applied it to N-body simulations. We compared
the filamentation of the observed vs. mock samples in metric space on scales
from 8 Mpc to 30 Mpc. Mock samples are closer to the observed sample than
random samples, and one of the mock samples behaves better than another one. We
also find that the observed sample has a large filamentation value at a scale
of 10 Mpc, which is not found from either mock samples or random samples. Key
words: filamentation, metric space, galaxy clusters, SDSS DR5