title: Mutual Effects of Radiation Field and Cosmic Rays on the Neutral and Molecular Interstellar Medium
creator: Wong, Yu Fung
subject: ddc-520
subject: 520 Astronomy and allied sciences
description: The photoelectric effect on dust grains is considered to be the dominant heating mechanism for the gas in the neutral and molecular interstellar medium. I investigate the effects of radiation fields with different intensities and colours on the photoelectric heating rate, and show that the near ultraviolet photons and optical photons has a significant contribution to the photoelectric heating rate in radiation fields in highly obscured regions in the interstellar medium. A new, self-consistent thermal and chemical model for the neutral and molecular interstellar medium is presented, and the mutual effects of radiation fields and cosmic rays on the thermal balance and chemistry of the gas are investigated. Including only the principle heating and cooling channels and the most observationally significant emission lines (e.g. CO pure rotational lines), the analytical approximations employed in the model makes it computationally fast and ideal to be incorporated into large-scale radiative transfer models for the propagation of starlight in galaxies. In addition, I show that the free electrons produced by cosmic ray ionisation of the interstellar gas particles lower the photoemission threshold of dust grains, thus boosting the photoelectric heating rate indirectly. Together with a simple semi-analytic spherical cloud model, the chemical model is applied to model the CO line emission in passive clouds in the nearby spiral galaxy NGC 628. The predicted CO line brightness is higher than the observed brightness by a factor of a few, and possible explanations for this overprediction are presented.
date: 2024
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserver/35391/1/YuFung_Wong_thesis.pdf
identifier: DOI:10.11588/heidok.00035391
identifier: urn:nbn:de:bsz:16-heidok-353913
identifier:   Wong, Yu Fung  (2024) Mutual Effects of Radiation Field and Cosmic Rays on the Neutral and Molecular Interstellar Medium.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/35391/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng