Universität zu Köln

Ebagezio, Stefano ORCID: 0000-0002-4505-5027 (2023). Molecular clouds and stellar feedback: an investigation of synthetic line and continuum emission maps. PhD thesis, Universität zu Köln.

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Abstract

Molecular clouds are complex systems and the search of adequate observational measurements to trace their evolution is still an open problem. In this thesis, we use produce synthetic emission maps of the 12CO 1-0, 13CO 1-0, [CI] 1-0, and [CII] lines, as well as of the FIR continuum emission, to test to which extent these emission measurements can be used as tracers of the evolutionary stage of molecular clouds. We use numerical simulations of molecular clouds performed within the SILCC-Zoom project. These simulations include detailed stellar feedback due to ionizing radiation, external magnetic fields, and a chemical network evolved on-the-fly. We compare two different chemical networks, NL97 and NL99, and we find that NL97, even though it does not include neutral carbon, more accurately reproduces the abundances of CO and C+. We then use NL97 in the rest of the work. We introduce a novel post-processing procedure for the C+ abundance using CLOUDY, essential in HII regions to account for the higher ionization states due to stellar radiation. Furthermore, we show that assuming chemical equilibrium results in H and H2 being underestimated and overestimated, respectively, by up to a factor of 2. The abundances of C+ and CO are also, respectively, underestimated and overestimated. This is reflected and amplified in the estimation of the CO and [CII] luminosity as well. We also investigate the capability of the L_CO/L_[CII] luminosity ratio to trace the H2 mass fraction in the clouds, but find no clear trend. We then investigate the [CII]/FIR ratio in HII regions and in entire clouds with stellar feedback. In young HII regions the drop of the [CII]/FIR intensity ratio is mainly due to the strong FIR emission produced by hot and dense dust, and the contemporary saturation of the [CII] line. In more evolved HII regions, the second ionization of carbon is the main reason for the low [CII]/FIR ratio. The evolution of this ratio is reflected in the evolution of the L_[CII]/L_FIR luminosity ratio in the entire clouds. This evolution can be schematized in three phases. Overall, L_[CII]/L_FIR is well correlated with the total stellar luminosity L_*tot. The relation between L_[CII]/L_FIR andL_*tot can be fitted with a power-law. When L_*tot is large, i.e., in evolved clouds which formed many massive stars, L_[CII]/L_FIR is particularly low, determining an observable [CII]-deficit in these clouds. However, this relation breaks when the total FIR luminosity stars decreasing as a consequence of the cloud dispersal caused by the stellar feedback. The aspect of HII regions in molecular clouds strongly depends on the geometry of the cloud, and on the line of sight. Indeed, a certain HII region can have different properties when observed from different LOS, and apparent HII regions, which are actually only the result of projection effects, can be observed.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Ebagezio, Stefano ebagezio@ph1.uni-koeln.de orcid.org/0000-0002-4505-5027 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-655552
Date:	2023
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 Interstellar medium English HII regions English Radiative transfer English
Date of oral exam:	26 April 2023
Referee:	Name Academic Title Seifried, Daniel PD Dr. Schilke, Peter Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/65555