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Interstellar medium properties and star formation in nearby galaxies
Includes bibliographical references.
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| Main Author: | |
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
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Department of Astronomy
2014
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| _version_ | 1867613202055954432 |
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| access_status_str | Open Access |
| author | Ianjamasimanana, Roger |
| author2 | De Blok, W J G |
| author_browse | De Blok, W J G Ianjamasimanana, Roger |
| author_facet | De Blok, W J G Ianjamasimanana, Roger |
| author_sort | Ianjamasimanana, Roger |
| collection | Thesis |
| description | Includes bibliographical references. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/8718 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:32:21.936Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2014 |
| publishDateRange | 2014 |
| publishDateSort | 2014 |
| 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:11427/8718 Interstellar medium properties and star formation in nearby galaxies Ianjamasimanana, Roger De Blok, W J G Jarrett, Thomas Includes bibliographical references. We study the properties of the interstellar medium (ISM) of nearby galaxies from The HI Nearby Galaxy Survey (THINGS) by analyzing the shapes of their HI emission velocity profiles. We apply a stacking method to increase the signal-to-noise (S/N) of the profiles and obtain what we call a super profile. We quantify all the relevant systematic effects that could confuse the interpretation of the shapes of the super profiles. We identify a sample of 22 galaxies from THINGS that are mostly free from these effects and analyze their super profile shapes. We derive super profiles from the entire HI disks of galaxies, inside and outside the optical radius r25, as a function of radius, column density, and star formation rate surface density. The super profiles can be described as the sum of a narrow and a broad Gaussian components. We associate the narrow component with the cold HI phase of the ISM and the broad component with the warm HI phase of the ISM. We find that the shapes of the super profiles correlate with star formation indicators such as metallicity, HK and far-UV near-UV colors. We also find that the mass fraction of the narrow component tends to be higher inside the optical radius r25. In addition, the velocity dispersions of the narrow and broad components decline exponentially with radius for virtually all the analyzed galaxies. Moreover, the flux ratio or mass ratio of the narrow and broad components, which serves as an estimate of the fraction of HI gas in the cold phase, tends to decrease with radius. Our results also show that regions having higher narrow component fractions usually corresponds to regions of higher HI or total (HI+H2) gas column density. Furthermore, the velocity dispersions of the broad and narrow components increase with increasing column density and star formation rate surface density. We have also investigated the physical mechanisms that can explain the observed width of the super profiles. These are supernova explosions (SNe), thermal effects from ultra-violet (UV) photons and magnetorotational instability (MRI). We find that SNe can explain the observed width of the super profile within the star forming disk (r25) and our data implies a supernova efficiency between 0.01 and 0.1. In the outer disk, the observed width of the super profiles can be attributed to thermal effects from extragalactic background UV photons. Finally, in most cases, MRI is not sufficient to explain the width of the super profile. 2014-10-21T14:22:20Z 2014-10-21T14:22:20Z 2014 Doctoral Thesis Doctoral PhD http://hdl.handle.net/11427/8718 eng application/pdf Department of Astronomy Faculty of Science University of Cape Town |
| spellingShingle | Ianjamasimanana, Roger Interstellar medium properties and star formation in nearby galaxies |
| thesis_degree_str | Doctoral |
| title | Interstellar medium properties and star formation in nearby galaxies |
| title_full | Interstellar medium properties and star formation in nearby galaxies |
| title_fullStr | Interstellar medium properties and star formation in nearby galaxies |
| title_full_unstemmed | Interstellar medium properties and star formation in nearby galaxies |
| title_short | Interstellar medium properties and star formation in nearby galaxies |
| title_sort | interstellar medium properties and star formation in nearby galaxies |
| url | http://hdl.handle.net/11427/8718 |
| work_keys_str_mv | AT ianjamasimananaroger interstellarmediumpropertiesandstarformationinnearbygalaxies |