Is nothing a sphere? Investigating the assumptions of the Alcock-Paczyński test for voids

Rozmarynowicz, Błażej (2024) Is nothing a sphere? Investigating the assumptions of the Alcock-Paczyński test for voids. Bachelor's Thesis, Physics.

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Abstract

In recent years, parts of the cosmological community have decided to approach the Hubble tension from a new angle, one focused on the study of cosmic voids – underdense regions, in which research of dark energy can flourish. Due to their relative emptiness, the dynamics of these voids are largely defined by their interactions with their external environments, which can lead to their preferred shapes and orientations. Some researchers argue cosmic voids can be stacked on top of each other to build a perfect sphere given local isotropy and large void quantities, allowing voids to be applied to the Alcock-Paczyński (AP) test, and significantly constraining the Hubble tension. In this thesis, we investigate the shape of voids on a local scale, focusing on an Illustris simulation. The simulation analysed in both physical and redshift space across 10 timesteps. We use DTFE and WVF to mark the voids, subsequently parametrizing them as ellipsoids. We find that the average stacked void is not perfectly spherical for a range of redshifts, when binned by volume and depth, and find them inadequate for the AP test. However these results are not statistically significant due to multiple biases inherent in the chosen methods. Finally, we find that the chosen methods result in volume fraction significantly larger than those present in the literature. We suggest further study into the assumptions of void use in the AP test, pushing the field forwards with confidence, rather than uncertainty.

Item Type:	Thesis (Bachelor's Thesis)
Supervisor name:	Weijgaert, M.A.M. van de
Degree programme:	Physics
Thesis type:	Bachelor's Thesis
Language:	English
Date Deposited:	12 Jul 2024 09:23
Last Modified:	12 Jul 2024 09:23
URI:	https://fse.studenttheses.ub.rug.nl/id/eprint/33242

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