Suri, Sümeyye
(2019).
Star Formation in the Orion A Molecular Cloud.
PhD thesis, Universität zu Köln.
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Abstract
Stars are found to form along and at junctions of filaments within molecular clouds. Filaments are elongated structures that have higher densities compared to their diffuse surroundings. Their first sightings date back to photographic plate observations of Barnard (1910). With the advances in astronomical instrumentation, observatories such as the Herschel Space Observatory were able to produce high sensitivity images of molecular clouds throughout the Galaxy. These images revealed that molecular clouds are pervaded with filaments on all scales. Furthermore, the filaments observed with Herschel in all molecular clouds are found to have common physical properties such as their width, bringing up an important question: “Can the properties of filamentary structure be universal?” In this thesis, I focused on the most nearby high-mass star forming region, the Orion A molecular cloud, and investigated the properties of its filamentary structure. Orion A is one of the most studied regions in the Galaxy and its filamentary nature was first presented with a large scale 13CO map in a study by Bally et al. (1987). Throughout this I made use of two large scale mapping surveys; the CARMA-NRO Orion Survey (Kong et al. 2018) and the C+ Square Degree Project. I also made use of the Herschel column density and temperature maps of the region (Stutz & Kainulainen 2015). In order to study the properties of the filaments, I first employed a structure detection algorithm, Discrete Persistent Structures Extractor (DisPerSE, Sousbie 2011), and investigated its performance on synthetic datasets. I found that in cases of low dynamic range and high levels of noise, DisPerSE can create artificial networks of filaments. Moreover, I developed a python based package, the Filament Characterization Package (FilChaP), that takes 2-dimensional (2D) or 3-dimensional (3D) datasets and DisPerSE filaments, and returns filament properties. FilChaP calculates filament length, width, skewness, kurtosis and curvature and is freely available for the community on github. Using FilChaP, I have investigated filament properties in different tracers (12CO, 13CO, C18O, [Cii]and dust column density). I found that filaments seen in C18O emission have a common width of 0.1 pc. The filament widths are independent from their central column densities, line masses and velocity dispersions. The majority of the dense cores are formed along the most gravitationally unstable filaments. I also found that the filaments are highly substructured and these substructures contribute to the turbulent velocity dispersion that provides support to the filaments and keeps them at a relatively constant width. This study revealed that, when calculating filament properties, it is important to separate structures along the line of sight by their velocities. In cases of filament widths calculated on the C18O integrated emission and dust column density maps, I found deviations from those filament widths calculated using the C18O datacube. These deviations are purely caused by the fact that integrated emission and column density maps cannot distinguish nearby structures or structures along the same line-of-sight at different velocities. Finally, I have looked at the [C ii] emission that mainly outlines the stellar feedback in the region. By comparing the radial profiles of C18O, 13CO, dust column density and [C ii] , I found that [C ii] emission almost always surrounds the emission from the dense gas indicating a chemical layering of different species that is typical for clumpy photo-dissociation regions.
| Item Type: | Thesis (PhD thesis) | ||||||||
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| URN: | urn:nbn:de:hbz:38-101620 | ||||||||
| Date: | 29 October 2019 | ||||||||
| Language: | English | ||||||||
| Faculty: | Faculty of Mathematics and Natural Sciences | ||||||||
| Divisions: | Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics I | ||||||||
| Subjects: | Natural sciences and mathematics Physics |
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| Date of oral exam: | 18 January 2019 | ||||||||
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| Refereed: | Yes | ||||||||
| URI: | http://kups.ub.uni-koeln.de/id/eprint/10162 |
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