Spectro-spatial efficiency profiling of volume phase holographic gratings and the detection of intermediate mass black holes with HARMONI on the E-ELT

Thesis

This thesis explores two interconnected areas of astrophysical research: the characterisation of volume phase holographic gratings (VPHGs) for use in the "high angular resolution monolithic optical and near-infrared integral field spectrograph" (HARMONI) and the detection of intermediate mass black holes (IMBHs) using the HARMONI instrument on the European Extremely Large Telescope (E-ELT). The first part of this research provides the most detailed measurements of spatial variations in VPHG transmission efficiency currently available, which is crucial for ensuring optimal performance of the HARMONI spectrograph. These measurements help to refine the design and application of VPHGs, contributing to improved data quality in upcoming observational campaigns.

The second part of the thesis focuses on a promising science case for HARMONI: the detection and observation of IMBHs in star clusters. IMBHs, hypothesised to bridge the gap between stellar-mass and supermassive black holes, remain an elusive component of the black hole population. Using high angular and spectral resolution integral field spectroscopy, this work aims to probe the line-of-sight velocity distributions of stars in the central regions of star clusters to identify kinematic signatures indicative of IMBHs. Simulations and observational strategies are presented to assess the capabilities of HARMONI in identifying IMBHs, with a focus on enhancing our understanding of black hole growth pathways and the role of IMBHs in galactic evolution.

This comprehensive investigation not only characterises key technological components for astronomical spectroscopy but also applies these advancements to pressing questions in black hole astrophysics, pushing the limits of our current observational capabilities.

Authors: Gooding, DJ

• DOI: 10.5287/ora-xm1w7e0pd
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: astronomical instrumentation; diffraction gratings; spectroscopy; black holes
• Subjects: Astrophysics; Astronomical instruments