The cosmic web in the Laduma field

Oelgeschlager, Tilman

The cosmic web in the Laduma field

Thesis / Dissertation

2025

Publisher

University of Cape Town

Department

Department of Astronomy

Faculty

Faculty of Science

Abstract

Cosmic web filaments are an intermediate density environment that have been shown to play a role in the evolution of galaxies. In order to accurately identify cosmic web filaments in a volume, a complete sample of galaxies with accurate distance measurements is required. For this reason, studies which identify filaments and investigate the properties of galaxies within them have been mostly restricted to the local Universe, where complete samples of galaxies with spectroscopic redshift measurements are available. In this thesis, I investigate filaments in the cosmic volume targeted by the Looking at the Distant Universe with the MeerKAT Array (LADUMA) survey at higher redshifts. LADUMA's ancillary data catalogue provides a limited sample of spectroscopic redshift measurements across LADUMA's target volume. I use the DisPerSE software package to identify large-scale structures. I use the Simba cosmological simulation to investigate the impact of using such a spectroscopic redshift catalogue on the output of DisPerSE. In particular, I test the effect of redshift-space distortions and their correction, incompleteness, sample bias and varying completeness on the accuracy of the large-scale structure found by DisPerSE. I find that the incompleteness of the LADUMA galaxy sample is the dominant cause of inaccuracy in the identified filament network. I test a method of improving the accuracy of the output of DisPerSE using photometric redshift measurements in the Simba simulation. I find that implementing this method with the photometric redshift measurements currently available in the LADUMA volume will not result in a more accurate filament network. Taking the simulation results into account, I use DisPerSE to create a map of filaments in the LADUMA target field using spectroscopic redshifts in the redshift range 0.2 < z < 0.4. Upon investigation, I find that galaxies in the LADUMA volume close to filaments have higher stellar masses and lower specific star formation rates compared to galaxies far from filaments. I find the same trends for galaxies and filaments in the Simba simulation volume. The increase in the stellar mass of galaxies toward filaments is found to be the primary driver for the corresponding decrease in specific star formation rate in both simulations and observations.

Keywords

Cosmic web

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