Universität zu Köln

Keilmann, Eduard ORCID: 0000-0003-1735-2021 (2025). The Genesis of Stars: From Giant Molecular Clouds to Star-Forming Cores. PhD thesis, Universität zu Köln.

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Abstract

Understanding how stars and planets emerge from molecular clouds requires studying cloud formation, evolution, and destruction under gravity, spiral density waves, stellar feedback, magnetic fields, and turbulence. This thesis investigates molecular cloud formation, star formation, and feedback processes on scales from individual clouds in the Milky Way to giant molecular clouds (GMCs) in the local‐group galaxy M33, using [C II], CO lines, and dust continuum observations and addresses four key questions: What drives molecular‐cloud assembly? How do cloud properties vary with galactic environment? How do these properties compare between the Milky Way and M33? And what mechanisms drive stellar feedback? I combine [C II] 158 μm, multiple CO rotational lines, H I data, and dust continuum maps. In Draco (a high‐latitude diffuse cloud), [C II] maps reveal shock‐induced emission from colliding H I flows, marking the onset of CO formation. In RCW79’s compact H II region S144, nested [C II] bubbles with slow, wind‐driven expansion exhibit a pronounced [C II]-deficit due to self-absorption, quantified via radiative‐transfer and SimLine modeling. For M33, I produce H_2 column‐density and dust‐opacity maps to derive the CO-to-H_2 conversion factor (X_CO), finding values comparable to or below the Galactic standard — contradicting simple metallicity-only scaling. A dendrogram-based machine‐learning identification of GMCs reveals a common upper size limit in both galaxies, the absence of >10^6 solar masses clouds in M33, and mass spectra that suggest gas‐density dependence. GMC physical properties (mass, surface density, morphology, etc.) show only little to basically no systematic variation with galactocentric radius or location within different galactic environments (such as spiral‐arms or the central region), suggesting cloud properties to appear insensitive to large-scale environments. The [C II] fine‐structure line proves a powerful tracer of early cloud assembly and feedback bubble dynamics. Stellar winds — not just radiation — play a critical role in shaping and dispersing molecular clouds. The universality of certain GMC characteristics, alongside negligible environmental differences, suggests that small-scale feedback may dominate over large-scale galactic conditions in regulating cloud life cycles.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Keilmann, Eduard e.keilmann@gmail.com orcid.org/0000-0003-1735-2021 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-785346
Date:	2025
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics I
Subjects:	Physics
Uncontrolled Keywords:	Keywords Language ISM; molecular clouds; star formation; [CII]; ionized carbon; GMCs; galaxy; Milky Way; M33; PDRs; Photo-dissociation region; HII region; dust; CO; structure; cloud formation; cloud destruction; cloud evolution; [CII]-deficit; English
Date of oral exam:	24 June 2025
Referee:	Name Academic Title Stutzki, Jürgen Prof. Dr. Schadschneider, Andreas Prof. Dr. Crewell, Susanne Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/78534