Master Thesis Defense by Laura Kristine Belling Fuglsang
Title: Preparing for 4G-PAQS: Exploring Quasar Diversity & Evaluating Flexure Compensation for the NTE Spectrograph
Abstract: This thesis consists of two main components: one focused on instrumentation and the other on quasars. The primary focus is on preliminary target analysis for the upcoming 4MOST–Gaia Purely Astrometric Quasar Survey (4G-PAQS). Recognizing the critical role of instrumentation in observational astrophysics, the thesis also incorporates work on the spectrograph for the Nordic Optical Telescope (NOT) Transient Explorer (NTE), currently under development at The Niels Bohr Institute. This combination of instrumentation and observational research is particularly relevant as NTE will be used for follow-up spectroscopy of 4G-PAQS targets, highlighting the intersection between instrument development and future astronomical observations.
Thus, the first part of this thesis focuses on instrumentation, specifically on optimizing the grating unit for the spectrograph in development for the NTE. The thesis seeks to find a solution to alleviate the effects of gravity flexure on the grating through tests and evaluations with an experimental setup resembling the grating unit positioned in the NTE spectrograph. A two-phase flexure compensation system (FCS) for alleviating gravitational flexure is proposed: Phase 1: An open-loop FCS, compensating for mapped flexure for each pointing of the telescope. Phase 2: A closed-loop FCS compensating for the residual flexure of phase 1, by utilizing bright sky lines. A preferred provisional mechanical design is determined. However, the mechanical design proves to constitute a challenge in compensating for flexure, as the deflection from gravitational flexure on the grating itself is larger than the motion range of the grating. It is crucial to further advance the mechanical design. Additional tests are proposed as the next steps to improve the mechanical design and optimize the FCS.
The second part of this thesis conducts a preliminary investigation of the 4G-PAQS targets, focusing on the red outlier population. The research aims to enhance the understanding of potential contaminants in the survey that may be misidentified as quasars and contribute to the scientific goals of the 4G-PAQS by identifying and characterizing red quasars, quasars with broad absorption lines (BALs) or Damped Lyman-alpha systems (DLAs), and rare quasars. The study implements the following key steps: (1) Proposes target morphology using synthetic colors of various objects in color-color diagrams. (2) Selects targets for spectroscopy, primarily from the red outlier color space, but also from potential contamination areas. (3) Acquires and analyzes spectral data of selected 4G-PAQS targets. A lower bound of ∼ 42% quasars in the 4G-PAQS sample is estimated and it is concluded that some degree of stellar and galactic contamination can be expected. From the identification of quasars with BALs, DLA and rare features among the 4G-PAQS targets, it is concluded that the quasar population may be more diverse than previously recognized and emphasize the critical importance of a large-scale, color-independent survey like 4G-PAQS in accurately characterizing the true diversity of the quasar population.
Supervisor:
- Johan Peter Uldall Fynbo, University of Copenhagen, Niels Bohr Institute
Censor:
- Frank Grundahl, Aarhus University