A High Spatial Resolution View of the Early Stages of Low Mass Star Formation: Understanding the Energetic Processes at Work

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A High Spatial Resolution View of the Early Stages of Low Mass Star Formation: Understanding the Energetic Processes at Work

O'Donoghue, Ross; (2024) A High Spatial Resolution View of the Early Stages of Low Mass Star Formation: Understanding the Energetic Processes at Work. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Molecules are found in almost all interstellar environments. Regions with high temperatures, ionisation rates, or intense UV radiation can be atomic in nature (e.g., coronal gas, stellar wind bubbles, hot ionised medium, HII regions). Where molecules exist, chemical reactions occur, and these reactions, strongly coupled to their environment, serve as powerful diagnostic tools. Observations and chemical modelling of molecules help us understand the current and historical conditions of the Interstellar Medium (ISM). Chapter 2 of this thesis presents a revised approach to cosmic ray treatment in the UCLCHEM chemical modelling code. We account for the dependency of cosmic ray ionisation and H2 dissociation rates on column density and include the production and reaction of cosmic ray-induced excited species on grains. This work examines how these treatments affect prestellar core chemistry, revealing significant impacts on chemical abundances, with ionisation dependency being the most critical factor. Comparisons with observational data show that the new treatments better reproduce observed chemical abundances than the standard approach. Chapter 3 probes the deuterated isotopologues of formaldehyde (H2CO) and the formyl ion (HCO+) in the Class 0/I protostar L1527 using ALMA data. With higher resolution than previous studies, we examine deuteration distribution on small scales, finding systematic variance in deuteration on 100-1000 au scales. Chapter 4 we present initial findings on the chemistry of S-bearing species around the Cep E-A intermediate-mass hot corino. We see emission is concentrated near the corino, with some outflow contribution. Our preliminary analysis suggests column densities of 1014 − 1016 cm−2 and temperatures above 50 K. Our results suggest that sulphur chemistry of IM hot corinos is similar to that of low-mass counterparts.

Type:	Thesis (Doctoral)
Qualification:	Ph.D
Title:	A High Spatial Resolution View of the Early Stages of Low Mass Star Formation: Understanding the Energetic Processes at Work
Open access status:	An open access version is available from UCL Discovery
Language:	English
Additional information:	Copyright © The Author 2024. 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
URI:	https://discovery.ucl.ac.uk/id/eprint/10197272