Astrophysical shocks and their astrochemical consequences in star forming regions

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Astrophysical shocks and their astrochemical consequences in star forming regions

James, Tomas Alexander; (2021) Astrophysical shocks and their astrochemical consequences in star forming regions. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Molecular gas is ubiquitous throughout the Interstellar Medium (ISM). The chemistry that produces this rich molecular inventory is highly coupled to the physical conditions of the gas in which the chemistry occurs. Consequently, one may use a coupled approach to understanding both the physics and chemistry of the ISM. This allows one to probe the physical conditions using observed molecular lines, alongside understanding the physical conditions and dynamics through inverse problems of the chemistry that these dynamics may drive. In this thesis, we firstly present in Chapter 2 a parameterised approach to modelling a Jump type (J-type) shock in astrophysical environments as part of the astrochemical code UCLCHEM. Our objective in this Chapter is to attempt to understand whether there are any observable differences between the chemistry that different shock types drive, and whether this can be used asrqd a tracer of shock type. We do this by comparing, across a grid of models, the chemistry from J-type shocks to equivalent Continuous type (C-type) shocks, before applying these models to the L1157-B2 clump in order to constrain the shock type and initial shock conditions within it. We secondly present in Chapter 3 spectroscopic observations obtained by collaborators using ALMA that observed 8 pointings within and around the Galactic Centre's Circumnuclear Disk (CND). We use the detected lines from 98 sub regions within these observations as inputs to a coupled radiative transfer Bayesian Inference algorithm that derives posterior distributions of the physical conditions within each region, specifcally temperature T, gas density nH and species column densities Nspec. This work's objective is to understand the physical conditions within the CND in detail in order to constrain the internal physical dynamics. Finally, we present a follow up study to that in Chapter 3 that couples the aforementioned inferred physical conditions to the shock models presented in Chapter 2. We attempt to recover the inferred physical conditions, as well as measured line fluxes, for three sources of interest using these shock models. Our objective is to assess whether the inferred and measured quantities are consistent with shock activity and, if so, what could be driving these shocks within the CND.

Type:	Thesis (Doctoral)
Qualification:	Ph.D
Title:	Astrophysical shocks and their astrochemical consequences in star forming regions
Event:	UCL
Open access status:	An open access version is available from UCL Discovery
Language:	English
Additional information:	Copyright © The Author 2021. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification:	UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI:	https://discovery.ucl.ac.uk/id/eprint/10140590