9 research outputs found
Evolution of the Pancaking Effect in a LCDM Cosmology
We explore the evolution of the large-scale anisotropy in the velocity field
caused by the gravitational pancaking effect assuming a LCDM universe. The
Millennium Run halo catalogs at four different redshifts, z=0, 0.5, 1 and z=2
are analyzed to find that the pancaking effect starts to intervene the
hierarchical structure formation at redshift z=2 when a characteristic pancake
scale is around 3 Mpc/h. It is also clearly shown how the degree and scale of
the pancaking effect changes with time. An analytic model based on the
Zel'dovich approximation is presented to explain quantitatively the evolution
of the velocity-pancake alignment. A cosmological implication of our finding
and a possibility of detecting a signal in real universe are discussed.Comment: accepted by ApJ, 21 pages, 6 figures, discussion and error analysis
improve
The Anisotropy in the Galaxy Velocity Field Originated from the Gravitational Pancaking Effect
We analyze the Millennium run semi-analytic galaxy catalog to explore
quantitatively the gravitational pancaking effect on the orientation of galaxy
velocity field. We first calculate the probability density distribution of the
cosine of the angle between the velocity of a field galaxy and the direction
normal to a local pancake plane which is determined using two nearest neighbor
field galaxies. A clear signal of alignment is detected for the case that the
pancake scale is in the range of Mpc. The tendency of the
velocity-pancake alignment is found to still exist when the pancakes are
determined using three neighbor galaxies, indicating that it has a spatial
coherence. The degree of the velocity-pancake alignment is shown to increase
with the velocity magnitude and the local density, while it decreases with the
separation distance from the galaxy to the pancake and disappears when the
pancake has a filamentary shape. A final conclusion is that our work may
provide another clue to understanding the large-scale structure in the
universe.Comment: accepted by ApJL, new analyses included, discussions improve
Reconstructing baryon oscillations
The baryon acoustic oscillation (BAO) method for constraining the expansion
history is adversely affected by non-linear structure formation, which washes
out the correlation function peak created at decoupling. To increase the
constraining power of low z BAO experiments, it has been proposed that one use
the observed distribution of galaxies to "reconstruct'' the acoustic peak.
Recently Padmanabhan, White and Cohn provided an analytic formalism for
understanding how reconstruction works within the context of Lagrangian
perturbation theory. We extend that formalism to include the case of biased
tracers of the mass and, because the quantitative validity of LPT is
questionable, we investigate reconstruction in N-body simulations. We find that
LPT does a good job of explaining the trends seen in simulations for both the
mass and for biased tracers and comment upon the implications this has for
reconstruction.Comment: 9 pages, 8 figure
Disentangling correlated scatter in cluster mass measurements
The challenge of obtaining galaxy cluster masses is increasingly being
addressed by multiwavelength measurements. As scatters in measured cluster
masses are often sourced by properties of or around the clusters themselves,
correlations between mass scatters are frequent and can be significant, with
consequences for errors on mass estimates obtained both directly and via
stacking. Using a high resolution 250 Mpc/h side N-body simulation, combined
with proxies for observational cluster mass measurements, we obtain mass
scatter correlations and covariances for 243 individual clusters along ~96
lines of sight each, both separately and together. Many of these scatters are
quite large and highly correlated. We use principal component analysis (PCA) to
characterize scatter trends and variations between clusters. PCA identifies
combinations of scatters, or variations more generally, which are uncorrelated
or non-covariant. The PCA combination of mass measurement techniques which
dominates the mass scatter is similar for many clusters, and this combination
is often present in a large amount when viewing the cluster along its long
axis. We also correlate cluster mass scatter, environmental and intrinsic
properties, and use PCA to find shared trends between these. For example, if
the average measured richness, velocity dispersion and Compton decrement mass
for a cluster along many lines of sight are high relative to its true mass, in
our simulation the cluster's mass measurement scatters around this average are
also high, its sphericity is high, and its triaxiality is low.
Our analysis is based upon estimated mass distributions for fixed true mass.
Extensions to observational data would require further calibration from
numerical simulations, tuned to specific observational survey selection
functions and systematics.Comment: 18 pages, 12 figures, final version to appear in MNRAS, helpful
changes from referee and others incorporate
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The Large-scale Structure of the Universe: Probes of Cosmology and Structure Formation
The usefulness of large-scale structure as a probe of cosmology and structure formation is increasing as large deep surveys in multi-wavelength bands are becoming possible. The observational analysis of large-scale structure guided by large volume numerical simulations are beginning to offer us complementary information and crosschecks of cosmological parameters estimated from the anisotropies in Cosmic Microwave Background (CMB) radiation. Understanding structure formation and evolution and even galaxy formation history is also being aided by observations of different redshift snapshots of the Universe, using various tracers of large-scale structure.This dissertation work covers aspects of large-scale structure from the baryon acoustic oscillation scale, to that of large scale filaments and galaxy clusters. First, I discuss a large- scale structure use for high precision cosmology. I investigate the reconstruction of Baryon Acoustic Oscillation (BAO) peak within the context of Lagrangian perturbation theory, testing its validity in a large suite of cosmological volume N-body simulations. Then I consider galaxy clusters and the large scale filaments surrounding them in a high resolution N-body simulation. I investigate the geometrical properties of galaxy cluster neighborhoods, focusing on the filaments connected to clusters. Using mock observations of galaxy clusters, I explore the the correlations of scatter in galaxy cluster mass estimates from multi-wavelength observations and different measurement techniques. I also examine the sources of the correlated scatter by considering the intrinsic and environmental properties of clusters