Universität zu Köln

Baby, Aleena ORCID: 0009-0005-2546-4981 (2024). Turbulent mixing in photodissociation regions. PhD thesis, Universität zu Köln.

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Abstract

Molecular clouds are dynamic environments where species are transported through random motions. To fully understand the physical conditions within these clouds, it is essential to quantify this transport. This study focused on the diffusion effects in the multi-fluid gas of photodissociation regions (PDRs) by considering turbulent, molecular, and thermal diffusion. To model the diffusion effects in a PDR, the KOSMA-⌧ PDR model is used. The KOSMA-⌧ PDR model simulta- neously solves the chemistry, level populations, and energy balance in a spherical geometry. This model included energy balance, cosmic ray ionization, CO and H2 self-shielding, photodestruction process, H2 formation, gas-dust interactions, and dust surface chemistry. This model derived the limits of the coherence length of turbulent diffusion and the total diffusion coe�cient as a function of the radius of the cloud. By ex- amining the impact of diffusion flows on chemical processes within the PDRs, this study found that diffusion can increase surface temperature and modify chemical pathways compared to a scenario without diffusion. The diffusion flows facilitate the transportation of H2 and CO molecules from lower temperature to higher tem- perature regions. As a consequence, H – H2 transition and C+ – C – CO transition shift towards the surface, in contrast to a situation where diffusion is absent. This diffusion-induced shift substantially influences the chemistry of the PDR. The chemistry of electrons, H, H2, C+, C, CO, CH, CH+, O, and OH show a significant impact when diffusion is added. C, C+, CS+, and HCO+, and their isotopologues, show changes (� 10%) in the integrated intensities. The integrated line intensity ratio of 13CO (1 -> 0)/ 12CO(1 -> 0), [12CII]/12CO(1 -> 0) and [12CI]/12CO(1 -> 0) shows <= 30% change when diffusion is added. Observations with telescopes such as ALMA or JWST can verify these changes in the intensity of specific organic molecules, allowing for investigating non-stationary chemistry e↵ects resulting from the diffusion of gas in the PDR.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Baby, Aleena aleenababy839@gmail.com orcid.org/0009-0005-2546-4981 UNSPECIFIED
Contributors:	Contribution Name Email Thesis advisor Ossenkopf-Okada, Priv.-Doz. Dr. Volker ossk@ph1.uni-koeln.de
URN:	urn:nbn:de:hbz:38-720655
Date:	26 January 2024
Publisher:	KUPS
Place of Publication:	KUPS
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 Molecular clouds English Diffusion English chemistry English photon dominated regions English photodissociation regions(PDR) English Astrochemistry English ISM abundances English ISM chemistry English ISM molecules English
Date of oral exam:	7 November 2023
Referee:	Name Academic Title Ossenkopf-Okada, Volker Priv.-Doz. Dr. Schilke, Peter Prof. Dr.
Related URLs:	Conference
Funders:	Collaborative research Centre 956, sub-project [C01], funded by the DFG- Project ID 184018867
Projects:	Collaborative research Centre 956, sub-project [C01], funded by the DFG- Project ID 184018867
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/72065