HI analysis of resolved galaxies in the MeerKAT Absorption Line Survey
- Authors: Maina, Eric Kamau
- Date: 2024-10-11
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466701 , vital:76771 , DOI https://doi.org/10.21504/10962/466701
- Description: This doctoral thesis examines two galaxy groups, Klemola 31 and UGC439, leveraging the observational capabilities of the MeerKAT Absorption Line Survey (MALS). The focus was on studying the interstellar medium, specifically the neutral hydrogen (H i) content, distribution, density, and dynamics, through high spatial resolution observations of these groups, and therefore offering insights into the complex processes affecting galaxy evolution in different environments. To make use of an additional tool, the absorption line characteristics of Hi in the two observed systems were analysed and compared with the kinematics and the morphology as induced by the observation of the Hi emission line in the same systems. For Klemola 31, this thesis identifies significant Hi deficiencies and interactions between member galaxies, with notable evidence of tidal interactions between Klemola 31 A and Klemola 31 B as well as ESO400-11 and LEDA2807038; and possible ram-pressure stripping in ESO400-13. The combined analysis of the Hi in emission and absorption indicates the presence of an extraplanar and potential intra-group medium in the group. The UGC439 group was observed in the commissioning phase of the MeerKAT array, revealing contrasting Hi distributions, with the central three galaxies indicating Hi excess while the peripheral galaxies indicating Hi deficiencies. There are two Hi clouds, one close to the central three galaxies and the other to the north. In this case, the observations are consistent with an Hi absorption system from within the disk of a galaxy. This thesis also highlights the necessity for further high spatial and spectral resolution observations to further reveal the intricacies of gas dynamics and its critical role in the life-cycle of galaxies. It serves as an outlook for further studies of the Hi environment of galaxies by combining absorption and emission line studies as first provided by MALS and ultimately by deep Hi surveys with the Square Kilometre Array. This thesis is organised into four chapters. The first chapter details a few concepts and background information about the physics of galaxy evolution. Chapter two talks about Klemola 31 galaxy group, where we start by describing our observation, data reduction and source finding. Thereafter, we explore the Hi morphology and kinematics of this group. In Chapter Three, we turn our attention to UGC439 galaxy group and organise it in a similar manner. A summary and comparison of the two groups is presented in Chapter 4. , Thesis (PhD) -- Faculty of Science, Physics and Electronics, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Maina, Eric Kamau
- Date: 2024-10-11
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466701 , vital:76771 , DOI https://doi.org/10.21504/10962/466701
- Description: This doctoral thesis examines two galaxy groups, Klemola 31 and UGC439, leveraging the observational capabilities of the MeerKAT Absorption Line Survey (MALS). The focus was on studying the interstellar medium, specifically the neutral hydrogen (H i) content, distribution, density, and dynamics, through high spatial resolution observations of these groups, and therefore offering insights into the complex processes affecting galaxy evolution in different environments. To make use of an additional tool, the absorption line characteristics of Hi in the two observed systems were analysed and compared with the kinematics and the morphology as induced by the observation of the Hi emission line in the same systems. For Klemola 31, this thesis identifies significant Hi deficiencies and interactions between member galaxies, with notable evidence of tidal interactions between Klemola 31 A and Klemola 31 B as well as ESO400-11 and LEDA2807038; and possible ram-pressure stripping in ESO400-13. The combined analysis of the Hi in emission and absorption indicates the presence of an extraplanar and potential intra-group medium in the group. The UGC439 group was observed in the commissioning phase of the MeerKAT array, revealing contrasting Hi distributions, with the central three galaxies indicating Hi excess while the peripheral galaxies indicating Hi deficiencies. There are two Hi clouds, one close to the central three galaxies and the other to the north. In this case, the observations are consistent with an Hi absorption system from within the disk of a galaxy. This thesis also highlights the necessity for further high spatial and spectral resolution observations to further reveal the intricacies of gas dynamics and its critical role in the life-cycle of galaxies. It serves as an outlook for further studies of the Hi environment of galaxies by combining absorption and emission line studies as first provided by MALS and ultimately by deep Hi surveys with the Square Kilometre Array. This thesis is organised into four chapters. The first chapter details a few concepts and background information about the physics of galaxy evolution. Chapter two talks about Klemola 31 galaxy group, where we start by describing our observation, data reduction and source finding. Thereafter, we explore the Hi morphology and kinematics of this group. In Chapter Three, we turn our attention to UGC439 galaxy group and organise it in a similar manner. A summary and comparison of the two groups is presented in Chapter 4. , Thesis (PhD) -- Faculty of Science, Physics and Electronics, 2024
- Full Text:
- Date Issued: 2024-10-11
A Bayesian approach to tilted-ring modelling of galaxies
- Authors: Maina, Eric Kamau
- Date: 2020
- Subjects: Bayesian statistical decision theory , Galaxies , Radio astronomy , TiRiFiC (Tilted Ring Fitting Code) , Neutral hydrogen , Spectroscopic data cubes , Galaxy parametrisation
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/145783 , vital:38466
- Description: The orbits of neutral hydrogen (H I) gas found in most disk galaxies are circular and also exhibit long-lived warps at large radii where the restoring gravitational forces of the inner disk become weak (Spekkens and Giovanelli 2006). These warps make the tilted-ring model an ideal choice for galaxy parametrisation. Analysis software utilizing the tilted-ring-model can be grouped into two and three-dimensional based software. Józsa et al. (2007b) demonstrated that three dimensional based software is better suited for galaxy parametrisation because it is affected by the effect of beam smearing only by increasing the uncertainty of parameters but not with the notorious systematic effects observed for two-dimensional fitting techniques. TiRiFiC, The Tilted Ring Fitting Code (Józsa et al. 2007b), is a software to construct parameterised models of high-resolution data cubes of rotating galaxies. It uses the tilted-ring model, and with that, a combination of some parameters such as surface brightness, position angle, rotation velocity and inclination, to describe galaxies. TiRiFiC works by directly fitting tilted-ring models to spectroscopic data cubes and hence is not affected by beam smearing or line-of-site-effects, e.g. strong warps. Because of that, the method is unavoidable as an analytic method in future Hi surveys. In the current implementation, though, there are several drawbacks. The implemented optimisers search for local solutions in parameter space only, do not quantify correlations between parameters and cannot find errors of single parameters. In theory, these drawbacks can be overcome by using Bayesian statistics, implemented in Multinest (Feroz et al. 2008), as it allows for sampling a posterior distribution irrespective of its multimodal nature resulting in parameter samples that correspond to the maximum in the posterior distribution. These parameter samples can be used as well to quantify correlations and find errors of single parameters. Since this method employs Bayesian statistics, it also allows the user to leverage any prior information they may have on parameter values.
- Full Text:
- Date Issued: 2020
- Authors: Maina, Eric Kamau
- Date: 2020
- Subjects: Bayesian statistical decision theory , Galaxies , Radio astronomy , TiRiFiC (Tilted Ring Fitting Code) , Neutral hydrogen , Spectroscopic data cubes , Galaxy parametrisation
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/145783 , vital:38466
- Description: The orbits of neutral hydrogen (H I) gas found in most disk galaxies are circular and also exhibit long-lived warps at large radii where the restoring gravitational forces of the inner disk become weak (Spekkens and Giovanelli 2006). These warps make the tilted-ring model an ideal choice for galaxy parametrisation. Analysis software utilizing the tilted-ring-model can be grouped into two and three-dimensional based software. Józsa et al. (2007b) demonstrated that three dimensional based software is better suited for galaxy parametrisation because it is affected by the effect of beam smearing only by increasing the uncertainty of parameters but not with the notorious systematic effects observed for two-dimensional fitting techniques. TiRiFiC, The Tilted Ring Fitting Code (Józsa et al. 2007b), is a software to construct parameterised models of high-resolution data cubes of rotating galaxies. It uses the tilted-ring model, and with that, a combination of some parameters such as surface brightness, position angle, rotation velocity and inclination, to describe galaxies. TiRiFiC works by directly fitting tilted-ring models to spectroscopic data cubes and hence is not affected by beam smearing or line-of-site-effects, e.g. strong warps. Because of that, the method is unavoidable as an analytic method in future Hi surveys. In the current implementation, though, there are several drawbacks. The implemented optimisers search for local solutions in parameter space only, do not quantify correlations between parameters and cannot find errors of single parameters. In theory, these drawbacks can be overcome by using Bayesian statistics, implemented in Multinest (Feroz et al. 2008), as it allows for sampling a posterior distribution irrespective of its multimodal nature resulting in parameter samples that correspond to the maximum in the posterior distribution. These parameter samples can be used as well to quantify correlations and find errors of single parameters. Since this method employs Bayesian statistics, it also allows the user to leverage any prior information they may have on parameter values.
- Full Text:
- Date Issued: 2020
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