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- Carl, Tadeus, 1992
(författare)
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Astrochemical Investigations of Complex Organics in Cold Molecular Cloud Cores
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Astrochemistry is the study of the formation and evolution of molecules in the interstellar medium (ISM) of the Milky Way and other galaxies. Molecules start to accumulate in the coldest and densest regions of the ISM, namely molecular clouds, and as of this date, 307 interstellar molecules are identified. The major focus of this thesis is on a particular group of interstellar molecules, so-called complex organic molecules (COMs), i.e., carbon-bearing molecules composed of at least six atoms. Interstellar COMs and other molecules are studied by a combination of observations, experiments, and models, with the focus of this thesis being on observations. Another focus will be on observations of COMs in very cold (< 10 K) and dense (> 10e5 cm−3) molecular cloud regions. This thesis is separated into two parts: part I is giving an overview about various important concepts and methods related to the detection, identification, and analysis of interstellar molecules (chapters 1 – 4), and part II is presenting the published paper this thesis is based on. Chapter 1 provides some background to my motivation to obtain a degree in astrochemistry, and to some basic concepts related to the formation of interstellar molecules. Some fundamental physical concepts widely used throughout this work will be introduced in that chapter as well. Chapter 2 introduces some important concepts and methods related to the derivation of molecular abundances from radio astronomical observations. Chapter 3 then gives a brief summary of the published paper this thesis is based on. Lastly, chapter 4 introduces some currently running and future projects (which I am part of) with the goal to add to the overall understanding of COM formation in the cold ISM.
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| 2. |
- Carl, Tadeus, 1992, et al.
(författare)
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Deep search for glycine conformers in Barnard 5
- 2023
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 524:4, s. 5993-6003
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Tidskriftsartikel (refereegranskat)abstract
- One of the most fundamental hypotheses in astrochemistry and astrobiology states that crucial biotic molecules like glycine (NH2CH2COOH) found in meteorites and comets are inherited from early phases of star formation. Most observational searches for glycine in the interstellar medium have focused on warm high-mass molecular cloud sources. However, recent studies suggest that it might be appropriate to shift the observational focus to cold low-mass sources. We aim to detect glycine towards the so-called methanol hotspot in the Barnard 5 dark cloud. The hotspot is a cold source (Tgas ≈ 7.5 K) with yet high abundances of complex organic molecules (COMs) and water in the gas phase. We carried out deep pointed observations with the Onsala 20 m telescope, targeting several transitions of glycine conformers I and II (Gly-I and Gly-II) in the frequency range 70.2-77.9 GHz. No glycine lines are detected towards the targeted position, but we use a line stacking procedure to derive sensitive abundance upper limits w.r.t. H2 for Gly-I and Gly-II, i.e. ≤(2-5) × 10-10 and ≤(0.7-3) × 10-11, respectively. The obtained Gly-II upper limits are the most stringent for a cold source, while the Gly-I upper limits are mostly on the same order as previously measured limits. The measured abundances w.r.t. H2 of other COMs at the B5 methanol hotspot range from 2 × 10-10 (acetaldehyde) to 2 × 10-8 (methanol). Hence, based on a total glycine upper limit of (2-5) × 10-10, we cannot rule out that glycine is present but undetected.
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