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Molecular Emission in Active Centres of Nearby Galaxies

Kelly, GJ; (2016) Molecular Emission in Active Centres of Nearby Galaxies. Doctoral thesis , UCL (University College London). Green open access

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Abstract

The work of this thesis focuses on observations of molecular rotational lines, which are used to uncover the properties of some of the most extreme regions of nearby galaxies. We complete this by both direct analysis of the observations, and using a suite of astrochemical models. We study the distribution of CS in two nearby starburst galaxies, NGC 6946 and NGC 3079. Two low-J lines of CS are observed with the IRAM-30m telescope in a region spanning 50′′ about the centre of each galaxy. Both lines have a high critical density that makes CS a good tracer of dense, star-forming gas. Through LTE analysis and a coupled radiative transfer-chemical modelling, we find a temperature and density gradient from the centre of NGC 6946 to the offset pointings. In NGC 3079, we find uniform temperature. We also present observations of SiO and HNCO in nearby galaxy NGC 1068 from the Plateau de Bure interferometer (PdBI). We see four clear peaks, one for each molecule to both the west and the east of the AGN. From a detailed chemical modelling we find that a high SiO abundance and low HNCO indicate a fast shock, while high HNCO and low SiO indicates either a slow shock or warm, dense, non-shocked gas. Comparing to observations, the east is therefore likely to contain gas that is heavily shocked. Gas to the west may be non-shocked, or maybe undergoing a much milder shock event. We complete a radiative transfer modelling. Taking into account these results, the milder shock event is the more likely of the two. Finally, ALMA observations of the distribution of several molecules in NGC 1068 are analysed. These molecules trace different components of the molecular gas in the AGN, circumnuclear disc and starburst ring. Spectral analysis of each molecule, and the ratio between molecules are used to determine galaxy properties and how these vary from region to region.

Type: Thesis (Doctoral)
Title: Molecular Emission in Active Centres of Nearby Galaxies
Event: UCL
Open access status: An open access version is available from UCL Discovery
Language: English
UCL classification: UCL > Provost and Vice Provost Offices
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/1532148
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