Macquarie University
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Probing the galactic ISM in OH absorption

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posted on 2022-03-28, 21:09 authored by Anita Petzler
We examine the four 2π3/2, J = 3/2 ground state transitions of the hydroxyl radical (OH) along 15 sightlines through the Milky Way disk towards bright background continuum sources. We find that the OH gas along these sightlines is optically thin, consistent with the findings from the Southern Parkes Large Area Survey in Hydroxyl (SPLASH) pilot region]. We present a partially automated method for Gaussian decomposition of our spectra which identified 55 components across 28 OH-containing clouds. Three of these OH clouds had no associated 12CO emission (CO data from NANTEN).We test two methods of finding excitation temperature: a modified ‘on-off’ method, and a method where the excitation temperatures and column densities are solved for numerically .Neither method constrained Tex well. Column densities were calculated based on a range of possibleexcitation temperatures (Tex (1667) = 5-15 K), and conversions to N(H2) were made. N(OH) values were found to range from 1 - 40 x 1014cm-2, corresponding to N(H2) values ranging from1 - 40 x 1021 cm-2. We discuss our results in the context of CO-dark H2, and outline future directions for our work.


Table of Contents

1. Introduction -- 2. Observations and data reduction -- 3. Gaussian decomposition -- 4. Results and discussion -- 5. Conclusions -- Appendices -- References.


Bibliography: pages 59-66 Empirical thesis.

Awarding Institution

Macquarie University

Degree Type

Thesis MRes


MRes, Macquarie University, Faculty of Science and Engineering, Department of Physics and Astronomy

Department, Centre or School

Department of Physics and Astronomy

Year of Award


Principal Supervisor

Joanne Dawson

Additional Supervisor 1

Cormac Purcell


Copyright Anita Petzler 2018. Copyright disclaimer:




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