Cosmology with underdensities of the cosmic web
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Date
19/08/2019Author
Demchenko, Vasiliy Grigoriyvich
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Abstract
This thesis explores the utilisation of underdense regions of the Cosmic Web
as a tool for studying cosmology. Underdensities, known as cosmic voids,
provide a complementary approach for understanding the large-scale structure
of our Universe, as well as providing a unique environment to explore the
effects of dark energy. An application of the spherical model to void evolution
is presented, showcasing its ability to provide non-linear density and velocity
profiles for voids. This methodology is then applied in order to reconstruct the
initial conditions of the void using a late-time void density profile. Using this
reconstruction, the spherical model yields non-linear late-time velocity profiles
which are used to predict redshift-space distortions around voids, showing the
capacity to constrain cosmological parameters using measurements in the non-linear
regime. Furthermore, this thesis investigates how cosmologists can utilise
the advances of weak gravitational lensing to exploit the underdensities of the
Universe. A study of the weak lensing measurement around voids is presented
with a focus on the SLICS simulation suite and the KiDS and GAMA surveys.
A watershed void finding algorithm, zobov, is applied to both the simulations
and data, showing that the geometry of the GAMA survey does not lend well to
extracting a weak lensing signal from voids due to limitations from both the survey
volume and geometry. In contrast, projected underdensities, known as troughs,
and the full, projected density spectrum, known as Density Split Statistics, are
both shown to yield great potential as cosmological tools. The final chapter
of this thesis investigates the use of this novel approach to explore non-ΛCDM
cosmologies using the cosmo-SLICS simulations, showing how underdensities can
potentially constrain the equation-of-state of dark energy with a higher precision
than overdense regions. Chapter 1 of this thesis provides a brief overview of
cosmology, while Chapter 2 introduces the theory of weak gravitational lensing.
Chapter 3 discusses the spherical model applied to void evolution and redshift-space
distortions around voids, while Chapter 4 explores the weak gravitational
lensing signal around voids in simulations and data. Chapter 5 utilises a suite of
simulations to investigate the sensitivity of Density Split Statistics to dark energy
models.