241 research outputs found
Cosmological Parameters from Observations of Galaxy Clusters
Studies of galaxy clusters have proved crucial in helping to establish the
standard model of cosmology, with a universe dominated by dark matter and dark
energy. A theoretical basis that describes clusters as massive,
multi-component, quasi-equilibrium systems is growing in its capability to
interpret multi-wavelength observations of expanding scope and sensitivity. We
review current cosmological results, including contributions to fundamental
physics, obtained from observations of galaxy clusters. These results are
consistent with and complementary to those from other methods. We highlight
several areas of opportunity for the next few years, and emphasize the need for
accurate modeling of survey selection and sources of systematic error.
Capitalizing on these opportunities will require a multi-wavelength approach
and the application of rigorous statistical frameworks, utilizing the combined
strengths of observers, simulators and theorists.Comment: 53 pages, 21 figures. To appear in Annual Review of Astronomy &
Astrophysic
A Multi-Code Analysis Toolkit for Astrophysical Simulation Data
The analysis of complex multiphysics astrophysical simulations presents a
unique and rapidly growing set of challenges: reproducibility, parallelization,
and vast increases in data size and complexity chief among them. In order to
meet these challenges, and in order to open up new avenues for collaboration
between users of multiple simulation platforms, we present yt (available at
http://yt.enzotools.org/), an open source, community-developed astrophysical
analysis and visualization toolkit. Analysis and visualization with yt are
oriented around physically relevant quantities rather than quantities native to
astrophysical simulation codes. While originally designed for handling Enzo's
structure adaptive mesh refinement (AMR) data, yt has been extended to work
with several different simulation methods and simulation codes including Orion,
RAMSES, and FLASH. We report on its methods for reading, handling, and
visualizing data, including projections, multivariate volume rendering,
multi-dimensional histograms, halo finding, light cone generation and
topologically-connected isocontour identification. Furthermore, we discuss the
underlying algorithms yt uses for processing and visualizing data, and its
mechanisms for parallelization of analysis tasks.Comment: 18 pages, 6 figures, emulateapj format. Resubmitted to Astrophysical
Journal Supplement Series with revisions from referee. yt can be found at
http://yt.enzotools.org
Constraining the growth rate of structure with phase correlations
We show that correlations between the phases of the galaxy density field in
redshift space provide additional information about the growth rate of
large-scale structure that is complementary to the power spectrum multipoles.
In particular, we consider the multipoles of the line correlation function
(LCF), which correlates phases between three collinear points, and use the
Fisher forecasting method to show that the LCF multipoles can break the
degeneracy between the measurement of the growth rate of structure and the
amplitude of perturbations that is present in the power spectrum
multipoles at large scales. This leads to an improvement in the measurement of
and by up to 220 per cent for and up to 50 per cent for at redshift , with respect to power spectrum
measurements alone for the upcoming generation of galaxy surveys like DESI and
Euclid. The average improvements in the constraints on and for
are per cent for the DESI
BGS sample with mean redshift , per cent for the
DESI ELG sample with , and per cent for the Euclid
H galaxies with . For , the average improvements are per cent for the
DESI BGS sample and per cent for both the DESI ELG and Euclid
H galaxies.Comment: 28 pages, 13 figures, 2 tables. v2 has additional discussion on
model-independence of the forecasts. v3 matches the MNRAS accepted versio
Interactive Visual Analytics for Large-scale Particle Simulations
Particle based model simulations are widely used in scientific visualization. In cosmology, particles are used to simulate the evolution of dark matter in the universe. Clusters of particles (that have special statistical properties) are called halos. From a visualization point of view, halos are clusters of particles, each having a position, mass and velocity in three dimensional space, and they can be represented as point clouds that contain various structures of geometric interest such as filaments, membranes, satellite of points, clusters, and cluster of clusters.
The thesis investigates methods for interacting with large scale data-sets represented as point clouds. The work mostly aims at the interactive visualization of cosmological simulation based on large particle systems. The study consists of three components: a) two human factors experiments into the perceptual factors that make it possible to see features in point clouds; b) the design and implementation of a user interface making it possible to rapidly navigate through and visualize features in the point cloud, c) software development and integration to support visualization
Including parameter dependence in the data and covariance for cosmological inference
The final step of most large-scale structure analyses involves the comparison
of power spectra or correlation functions to theoretical models. It is clear
that the theoretical models have parameter dependence, but frequently the
measurements and the covariance matrix depend upon some of the parameters as
well. We show that a very simple interpolation scheme from an unstructured mesh
allows for an efficient way to include this parameter dependence
self-consistently in the analysis at modest computational expense. We describe
two schemes for covariance matrices. The scheme which uses the geometric
structure of such matrices performs roughly twice as well as the simplest
scheme, though both perform very well.Comment: 17 pages, 4 figures, matches version published in JCA
Doctor of Philosophy
dissertationA broad range of applications capture dynamic data at an unprecedented scale. Independent of the application area, finding intuitive ways to understand the dynamic aspects of these increasingly large data sets remains an interesting and, to some extent, unsolved research problem. Generically, dynamic data sets can be described by some, often hierarchical, notion of feature of interest that exists at each moment in time, and those features evolve across time. Consequently, exploring the evolution of these features is considered to be one natural way of studying these data sets. Usually, this process entails the ability to: 1) define and extract features from each time step in the data set; 2) find their correspondences over time; and 3) analyze their evolution across time. However, due to the large data sizes, visualizing the evolution of features in a comprehensible manner and performing interactive changes are challenging. Furthermore, feature evolution details are often unmanageably large and complex, making it difficult to identify the temporal trends in the underlying data. Additionally, many existing approaches develop these components in a specialized and standalone manner, thus failing to address the general task of understanding feature evolution across time. This dissertation demonstrates that interactive exploration of feature evolution can be achieved in a non-domain-specific manner so that it can be applied across a wide variety of application domains. In particular, a novel generic visualization and analysis environment that couples a multiresolution unified spatiotemporal representation of features with progressive layout and visualization strategies for studying the feature evolution across time is introduced. This flexible framework enables on-the-fly changes to feature definitions, their correspondences, and other arbitrary attributes while providing an interactive view of the resulting feature evolution details. Furthermore, to reduce the visual complexity within the feature evolution details, several subselection-based and localized, per-feature parameter value-based strategies are also enabled. The utility and generality of this framework is demonstrated by using several large-scale dynamic data sets
The Persistence of Large Scale Structures I: Primordial non-Gaussianity
We develop an analysis pipeline for characterizing the topology of large
scale structure and extracting cosmological constraints based on persistent
homology. Persistent homology is a technique from topological data analysis
that quantifies the multiscale topology of a data set, in our context unifying
the contributions of clusters, filament loops, and cosmic voids to cosmological
constraints. We describe how this method captures the imprint of primordial
local non-Gaussianity on the late-time distribution of dark matter halos, using
a set of N-body simulations as a proxy for real data analysis. For our best
single statistic, running the pipeline on several cubic volumes of size
, we detect at
confidence on of the volumes. Additionally we test our ability to
resolve degeneracies between the topological signature of and variation of and argue that correctly identifying nonzero
in this case is possible via an optimal template method.
Our method relies on information living at Mpc/h, a
complementary scale with respect to commonly used methods such as the
scale-dependent bias in the halo/galaxy power spectrum. Therefore, while still
requiring a large volume, our method does not require sampling long-wavelength
modes to constrain primordial non-Gaussianity. Moreover, our statistics are
interpretable: we are able to reproduce previous results in certain limits and
we make new predictions for unexplored observables, such as filament loops
formed by dark matter halos in a simulation box.Comment: 33+11 pages, 19 figures, code available at
https://gitlab.com/mbiagetti/persistent_homology_ls
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