20 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
Nearest neighbor vector analysis of sdss dr5 galaxy distribution
We present the Nearest Neighbor Distance (NND) analysis of SDSS DR5 galaxies.
We give NND results for observed, mock and random sample, and discuss the
differences. We find that the observed sample gives us a significantly stronger
aggregation characteristic than the random samples. Moreover, we investigate
the direction of NND and find that the direction has close relation with the
size of the NND for the observed sample.Comment: Natural Science, Vol.5, No.1 in January 201
Dense Galactic Superclusters Add New Structural Details to the Universe
At the American Astronomical Society meeting in Austin, Texas, Thursday, January 7, 1999, astronomers David Batuski and Chris Miller of the University of Maine, presented evidence of two relatively rare types of galaxy superclusters in a single colossal complex in the southern part of the constellation Aquarius. The complex consists of two long filaments, one of which is the longest such object yet seen, and a dense knot of clusters.
These findings add significantly to the emerging picture of large-scale structure in the present-day universe and provide some well-defined examples of structure that must be explained by processes in the fireball of the Big Bang. Future analysis of the knot of clusters, when studied in detail with three other similar clumps of clusters, may prove that some vast objects may be collapsing within our otherwise expanding universe
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
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
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
The cluster Abell 780: an optical view
The Abell 780 cluster, better known as the Hydra A cluster, has been
thouroughly analyzed in X-rays. However, little is known on its optical
properties. We derive the galaxy luminosity function (GLF) in this apparently
relaxed cluster, and search for possible environmental effects by comparing the
GLFs in various regions, and by looking at the galaxy distribution at large
scale around Abell 780. Our study is based on optical images obtained with the
ESO 2.2m telescope and WFI camera in the B and R bands, covering a total region
of 67.22x32.94 arcmin^2, or 4.235x2.075 Mpc^2 for a cluster redshift of 0.0539.
In a region of 500 kpc radius around the cluster centre, the GLF in the R band
shows a double structure, with a broad and flat bright part and a flat faint
end that can be fit by a power law with an index alpha=-0.85+-0.12 in the
20.25<R<21.75 interval. If we divide this 500 kpc radius region in North+South
or East+West halves, we find no clear difference between the GLFs in these
smaller regions. No obvious large scale structure is apparent within 5 Mpc from
the cluster, based on galaxy redshifts and magnitudes collected from the NED
database in a much larger region than that covered by our data, suggesting that
there is no major infall of material in any preferential direction. However,
the Serna-Gerbal method reveals the presence of a gravitationally bound
structure of 27 galaxies, which includes the cD, and of a more strongly
gravitationally bound structure of 14 galaxies. These optical results agree
with the overall relaxed structure of Abell 780 previously derived from X-ray
analyses.Comment: Accepted for publication in Astronomy & Astrophysic
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