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Title: Instrumentation for HARMONI and the mass ratios of ring galaxy systems
Author: Allen, Jamie
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2017
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HARMONI is the visible and near-infrared integral field spectrograph due to be one of the first light instruments on the European Extremely Large Telescope. The prototype HARMONI lens mounts were cryogenically tested, to measure the radial decentre of the lens as it was cooled to 130 K. Initial problems of the epoxy cracking the lens were solved by switching to a silicone RTV adhesive. The lens in the baseline mount design was found to move radially by 18 μm: just below the tightest radial positioning tolerance. The Oxford SWIFT Spectrograph spare camera was rebuilt using lens mounts based on the proposed HARMONI designs. A procedure to align spherical lenses to their mounts was developed that could position the lenses to within 10 μm both radially and axially. However, the performance of the camera did not meet expectations, as the lenses were moving in their mounts. This was attributed to either the adhesive or the cotton paper buffer between the lens and its mount; also, at least one bond had failed. These issues are thought to be solvable by using an automatic, rather than manual, adhesive dispenser, though this has yet to be proven. A commercial off-the-shelf shutter was also tested to see if it would work in the HARMONI cryostat. Although it could be used at these temperatures, it could not be made fully reliable. Its lifetime of 9321 actuations was also much lower than the estimated 88000 actuations for the lifetime of HARMONI. Ring galaxies are annulus-shaped galaxies thought to be formed from a disc galaxy when a companion galaxy passes directly through it close to its centre at a nearly-normal angle. The kinematics of three ring galaxies were measured from MUSE observations and used to estimate their dynamical masses. A simple analytic model was used to refine the fits to the kinematics, though this did not change the measured masses very much. Stellar population synthesis models were fit to the integrated spectrum of the companions of two of the ring galaxies to estimate their stellar masses via their mass-to-light ratios. The mass ratios of the companions to the rings were both found to have a lower bound of 1/6, though possibly increasing to 2/5 when dark matter is taken into account. This value is comparable to other observational results of ring galaxy mass ratios, and is within the range of values used for simulations of ring galaxy formation.
Supervisor: O'Brien, Kieran ; Thatte, Niranjan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available