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Exploring HI asymmetries in real and simulated galaxies
In the ΛCDM model of the Universe, galaxy-galaxy interactions and mergers are considered key drivers in their evolution. These dynamical events lead to peculiar and disturbed morphologies, which can be studied using morphometric statistics. The rotational 2D asymmetry parameter, adopted from optical...
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| Format: | Thesis |
| Language: | English |
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Department of Astronomy
2021
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| _version_ | 1867614334681612288 |
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| access_status_str | Open Access |
| author | Hank, Nadine A N |
| author2 | Blyth, Sarah-Louise |
| author_browse | Blyth, Sarah-Louise Hank, Nadine A N |
| author_facet | Blyth, Sarah-Louise Hank, Nadine A N |
| author_sort | Hank, Nadine A N |
| collection | Thesis |
| description | In the ΛCDM model of the Universe, galaxy-galaxy interactions and mergers are considered key drivers in their evolution. These dynamical events lead to peculiar and disturbed morphologies, which can be studied using morphometric statistics. The rotational 2D asymmetry parameter, adopted from optical studies, has recently been used to quantify asymmetries in the H i images of galaxies. This is useful since H i disks typically extend further than the stellar disks and are more sensitive to distortions from interactions. Asymmetries can also manifest in the 1D spectral domain, distorting the shape of the global H i profiles of galaxies. The shape of this profile is determined predominantly by the kinematics of the galaxy, and the H i spatial distribution to a lesser extent. By using archival H i data and simulations, we have begun investigating the systematics and uncertainties of using the 1D and 2D asymmetry parameters for merger studies. In this thesis, we present a new 1D measure of lopsidedness and examine the applicability of two different 2D asymmetry measures. We investigate the evolution of 2D asymmetry of the gas and stellar distributions in a simulated major merger event and demonstrate that the gas distribution registers the interaction before the stellar distribution is affected. We also find that the outer asymmetry of both distributions is considerably higher postmerger, whereas the intensity-weighted asymmetry returns to pre-merger values. We then explore how well the 1D and 2D parameters agree with visual classifications of asymmetry for a sample of 115 WHISP galaxies and observe that the 1D folding difference lopsidedness and the 2D intensity-weighted asymmetry parameters compare well with the visual classification of asymmetries in the H i profiles and images respectively. We examine the relationship between the 1D and 2D asymmetries in WHISP and find that the 1D folding difference lopsidedness and the 2D intensity-weighted asymmetry yield the strongest linear correlation between spectral and morphological asymmetries, with r = 0.53 after inclination cuts have been applied. Lastly, we investigate the location of interacting galaxies in asymmetry parameter space and find that the joint use of 1D and 2D parameters can separate most interacting galaxies from the non-interacting sample. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/33710 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:50:23.938Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2021 |
| publishDateRange | 2021 |
| publishDateSort | 2021 |
| publisher | Department of Astronomy |
| publisherStr | Department of Astronomy |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/33710 Exploring HI asymmetries in real and simulated galaxies Hank, Nadine A N Blyth, Sarah-Louise Deg, Nathan astronomy In the ΛCDM model of the Universe, galaxy-galaxy interactions and mergers are considered key drivers in their evolution. These dynamical events lead to peculiar and disturbed morphologies, which can be studied using morphometric statistics. The rotational 2D asymmetry parameter, adopted from optical studies, has recently been used to quantify asymmetries in the H i images of galaxies. This is useful since H i disks typically extend further than the stellar disks and are more sensitive to distortions from interactions. Asymmetries can also manifest in the 1D spectral domain, distorting the shape of the global H i profiles of galaxies. The shape of this profile is determined predominantly by the kinematics of the galaxy, and the H i spatial distribution to a lesser extent. By using archival H i data and simulations, we have begun investigating the systematics and uncertainties of using the 1D and 2D asymmetry parameters for merger studies. In this thesis, we present a new 1D measure of lopsidedness and examine the applicability of two different 2D asymmetry measures. We investigate the evolution of 2D asymmetry of the gas and stellar distributions in a simulated major merger event and demonstrate that the gas distribution registers the interaction before the stellar distribution is affected. We also find that the outer asymmetry of both distributions is considerably higher postmerger, whereas the intensity-weighted asymmetry returns to pre-merger values. We then explore how well the 1D and 2D parameters agree with visual classifications of asymmetry for a sample of 115 WHISP galaxies and observe that the 1D folding difference lopsidedness and the 2D intensity-weighted asymmetry parameters compare well with the visual classification of asymmetries in the H i profiles and images respectively. We examine the relationship between the 1D and 2D asymmetries in WHISP and find that the 1D folding difference lopsidedness and the 2D intensity-weighted asymmetry yield the strongest linear correlation between spectral and morphological asymmetries, with r = 0.53 after inclination cuts have been applied. Lastly, we investigate the location of interacting galaxies in asymmetry parameter space and find that the joint use of 1D and 2D parameters can separate most interacting galaxies from the non-interacting sample. 2021-08-06T07:19:46Z 2021-08-06T07:19:46Z 2021 2021-08-06T07:19:14Z Master Thesis Masters MSc http://hdl.handle.net/11427/33710 eng application/pdf Department of Astronomy Faculty of Science |
| spellingShingle | astronomy Hank, Nadine A N Exploring HI asymmetries in real and simulated galaxies |
| thesis_degree_str | Master's |
| title | Exploring HI asymmetries in real and simulated galaxies |
| title_full | Exploring HI asymmetries in real and simulated galaxies |
| title_fullStr | Exploring HI asymmetries in real and simulated galaxies |
| title_full_unstemmed | Exploring HI asymmetries in real and simulated galaxies |
| title_short | Exploring HI asymmetries in real and simulated galaxies |
| title_sort | exploring hi asymmetries in real and simulated galaxies |
| topic | astronomy |
| url | http://hdl.handle.net/11427/33710 |
| work_keys_str_mv | AT hanknadinean exploringhiasymmetriesinrealandsimulatedgalaxies |