Browsing by Author "Skelton, Rosalind"

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    Open Access
    Probing the role of environment and HI content in galaxy evolution: a multi-wavelength study of isolated and paired galaxies
    (2021) Bok, Jamie; Jarrett, Thomas; Skelton, Rosalind; Cluver, Michelle, Blyth, Sarah
    This thesis records a detailed examination of the impact of the merger-pair galaxy environment on both the neutral hydrogen (Hi ) and mid-infrared (MIR) properties of galaxies in the nearby Universe. Making use of publicly available Hi profiles from the ALFALFA survey I construct the first statistically significant samples of close-pair galaxies (348 Hi -optical and 282 Hi - Hi pairs), and contrast their Hi content and star formation (SF) properties with a statistically significant Hisub-sample of isolated galaxies (544 galaxies) from the AMIGA project (Analysis of the interstellar Medium in Isolated GAlaxies; Verdes-Montenegro et al. (2005)). I present the first study of pairs using WISE data, and specifically examine their location on the MIR star-formation rate-stellar mass sequence (SFR-M★), or star-forming main sequence (SFMS), as a way to study how the close-pair environment influences the build up of galaxy stellar mass via SF. I also present the first MIR SFMS for isolated galaxies from the AMIGA catalogue to serve as the precedent for secular evolution. I derive an Hi scaling relation for isolated galaxies using WISE stellar masses, and thereby establish a baseline predictor of Hi content that can be used to assess the impact of environment on Hi content when compared with samples of galaxies in different environments. I use this updated relation to determine the Hi deficiency of both my paired and isolated galaxies, and invoke galaxy morphology (visual and MIR bulge-to-total ratios), the AMIGA isolation parameters 휂 (local number density) and Q (tidal influence), star formation efficiency (SFE), and Hi profile asymmetries to more closely inspect how these properties might be additionally driving the observed differences between the deficiency distributions of these two samples, as well as SFMS location. I also provide an analysis of the quantified Hi profile asymmetries of my pair and isolated galaxy samples, exploring not only the prevalence of asymmetry in Hi profiles, but also the possibility of using Hi profile asymmetries to trace merger activity. I find enhanced profile asymmetries in my pair sample, and propose that high profile asymmetries may be used to infer merger activity/identify close galaxy pairs at high redshifts, in lieu of the typically used 2D Hi maps we have for galaxies at low and intermediate redshifts, which are currently still limited. What my thesis shows is that although we have a plethora of data available (and coming), the key is to optimise how we use it, both in the questions we pose, and in understanding its limitations. We currently have large data-sets of Hi profiles in the local Universe, which, when incorporated into a cohesive multi- wavelength study, provide important clues as to how Hi forms, influences, and is processed in galaxies. These are the studies informing our theories for galaxy evolution, providing the incentive for superior telescopes (e.g. SKA), and ultimately guiding our decision-making in how to proceed in our ongoing endeavour to understand our Universe.
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    The cosmic web in the Laduma field
    (2025) Oelgeschlager, Tilman; Blyth, Sarah-Louise; Skelton, Rosalind
    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.
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    Ultra-diffuse galaxy candidatesin stripe 82 clusters
    (2019) Makda, Nazir Ahmed Adam; Skelton, Rosalind; Blyth, Sarah
    The evolution of galaxies in the cluster environment is a complex process, with many outstanding questions. A wide range of galaxy morphologies, colours, sizes and luminosities are found in clusters, the least studied of which are the faint galaxy populations. Studying the faint end of the galaxy luminosity distribution may provide a valuable insight into the evolution of galaxies in cluster environments. The largest of these faint galaxies are classified as Ultra-Diffuse galaxies (UDGs). UDGs are low surface brightness galaxies with a very low stellar mass component, however they have sizes comparable to the Milky Way. These galaxies are hard to detect and classify as they are very faint. To survive in the cluster environments, where they have been observed, these galaxies must contain significant amounts of dark matter as the strong tidal fields would normally tear diffuse low-mass galaxies apart. The high abundance of UDGs in clusters has only recently been recognized, therefore identifying and measuring their properties is key to understanding how they are formed and continue to exist. In this thesis, I search for low surface brightness galaxies, spanning from typical dwarf galaxies to UDGs, in 16 low redshift (z< b/a >= 0.52. The number of faint galaxies in clusters follows a power-law with respect to the cluster halo mass, N ∝ M1.05±0.45, determined through bootstrap resampling. This shows that the number of UDG candidates increases as the cluster halo mass increases.