Astrochemical Investigations of the Methanol Hotspot in Barnard 5

Doktorsavhandling, 2026

The molecules present in the molecular clouds of the Milky Way and other galaxies are formed by a combination of gas phase reactions and grain surface reactions on interstellar dust grains. Especially at low temperatures, grain surface reactions become increasingly important for the formation of many molecules, giving rise to the formation of molecular ices around the grains. The molecules in the ice can be released into the gas phase by different desorption mechanisms, and once in the gas, they become observable via their rotational spectra. The focus of this thesis is on two particular groups of molecules: (1) complex organic molecules (COMs), i.e., carbon-bearing molecules composed of at least six atoms, and (2) sulfur-bearing molecules. Further focus is on observations of such molecules in the gas phase of cold (~ 10 K) and dense (~ 10⁵ cm^-3) molecular cloud regions using single-dish radio telescopes. The overall aim of the observations is to put constraints on the formation pathways and the desorption mechanisms of those groups of molecules at low temperatures, as many details of these processes are still not well established. 

In particular, the papers appended to this thesis utilized the OSO 20 m, IRAM 30 m, and Yebes 40 m telescopes to investigate the molecular content and chemistry in cold and dense gas at the so-called methanol hotspot in the Barnard 5 (B5) dark cloud (Perseus). The methanol hotspot is the position of maximum methanol emission in B5, and is generally characterized by very efficient ice desorption, releasing water, methanol (CH₃OH), and larger COMs into the gas phase. Paper A presents a deep search for glycine (NH₂CH₂COOH), i.e., the simplest biotic amino acid. Glycine could not be detected, but sensitive upper limits were derived. Paper B studies the distribution of several COMs around the methanol hotspot, showing that COMs are widely distributed in the area and likely released from ices by the same efficient desorption mechanism. Lastly, paper C investigates the sulfur budget and sulfur chemistry at the hotspot. The sulfur budget is significantly higher than towards other dark cloud sources while the chemistry is likely affected by the high gas phase water abundance.