Universität zu Köln

Yanitski, Craig Nicholas ORCID: 0009-0009-3294-6320 (2023). The Milky Way with kosmatau3d: Modelling the Galactic cooling lines using clumpy PDRs. PhD thesis, Universität zu Köln.

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Abstract

Given the number of large-scale Milky Way surveys of the dust continuum and spectroscopic line transitions, we are in a favourable position to test different models of the interstellar medium (ISM) in order to better understand and constrain its physics. While the numerous features of the Galactic ISM observation cannot be matched simultaneously by a test model, the large-scale structure and the typical line ratios and intensities should be reproduced in a statistically significant way. To that end, previous research has utilised the KOSMA-τ photon-dissociation region (PDR) code to fit the line emission as observed with COBE-FIRAS with very few assumptions and constraints. The basis of this work was the fractal structure of the ISM: a theory that accounts for the high surface-to-volume ratio as inferred from observations allowing the sophisticated post-processing of self-consistent model results. I have now extended this approach to arbitrary geometries in the novel PDR code kosmatau3d, which also accounts for the dust pumping, continuum emission, and absorption effects. The code uniquely accounts for the clumpy structure of the inhomogeneous ISM. I have used this code to model the molecular and atomic cold neutral medium (CNM) in the Milky Way using axisymmetric distributions of the dense and diffuse gas mass (traced with atomic and molecular hydrogen), average density, cosmic ray ionisation rate, and far-UV radiation. I find that much of the observed large-scale structure in the spectroscopic maps can be replicated in the synthetic observations, though there remains difficulty to fully model the self-absorption features toward the Galactic centre. I also find these kosmatau3d synthetic observations are able to replicate the molecular ring and certain Galactic arm features even without an explicit implementation of the spiral structure of the Milky Way. This suggests the structure seen in the galactic position-velocity diagram arises to a large extent from the rotation of the galaxy and the molecular ring, and thus offers insight into the interpretation of galactic longitude-velocity diagrams. I also summarise the benefit of using multiple transition lines in the constraining of the Milky Way parameters, how these constraints improve on and differ from previous work, and finally conclude with an outlook on this method of modelling and how well the Galactic cooling lines can be modelled using PDRs.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Yanitski, Craig Nicholas yanitski@ph1.uni-koeln.de orcid.org/0009-0009-3294-6320 161444663
URN:	urn:nbn:de:hbz:38-718501
Date:	21 December 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 Interstellar medium English Photo-dissociation regions English Astrophysical modelling English Radiative transfer English
Date of oral exam:	2 November 2023
Referee:	Name Academic Title Ossenkopf-Okada, Volker Priv.-Doz. Dr. Walch-Gassner, Stefanie Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/71850