School of Physics - Theses

Permanent URI for this collection

http://hdl.handle.net/11343/310

Filters

2023 1
1
Reset filters

Settings
Statistics
Citations
Author: Kenyon, Clare Emily Guinane × Subject: astrophysics × Subject: galaxies ×

Search Results

Now showing 1 - 1 of 1
  • Item
    Thumbnail Image
    Quasar Broad Emission Line Regions and Gravitational Microlensing
    Kenyon, Clare Emily Guinane ( 2023-08)
    This thesis has focussed on hydrogen and helium emission line generation in the Broad Emission Line Region (BELR) of quasars and also on the gravitationally lensed quasar LBQS1009-0252. Quasars are a class of galaxy characterised by an active nuclear region in which a high rate of accretion onto a central supermassive black hole results in the release of vast amounts of broadband energy over a prolonged period of time. These incredible luminosities—often up to 100,000 times that of a standard galaxy—make quasars some of the most distant, and therefore earliest, sources ever observed in the universe. The relatively tiny size of the innermost region, however, precludes direct observation, and so the physics and geometry of quasars remains enigmatic. Emitted by the accretion disk, light interacts with surrounding gasses in the BELR—so-named because light which is reprocessed and re-emitted from this region tends to be significantly broadened due to wholescale Doppler motions of the gas. As the first gas to ‘see’ light from the accretion disk, understanding and constraining the nature and dynamics of the BELR remains of interest in many astrophysical fields. Following methods pioneered by Ruff (2012), microphysical simulations (such as those produced by the photoionisation code, Cloudy) can be combined with observed spectral data of real sources to model hydrogen line emission from the BELR. This research has confirmed and built further upon the methods presented in Ruff (2012) through the use of updated code and new, high-quality NIR spectral data of 14 quasar sources acquired from the Flamingos-2 (F2) instrument on Gemini South at the Gemini Observatory. The thesis has also gone a step beyond the original method and includes the modelling and analysis of helium emission lines for the first time. Broadly, the results lend support to the conclusions presented in Ruff (2012): hydrogen lines tend to be produced optimally in regions of low incident ionising flux and high gas number density. Helium lines also appear to follow this trend, clustering in a similar parameter space, although there appears to be a tendency towards a flatter distribution across the value for maximum gas number density. This suggests that despite similarities in their physical production and spectral appearance, there are some slight differences in the behaviour of hydrogen and helium emission lines in the BELR, and it is prudent to analyse them separately where possible. This thesis also examined the double-image gravitationally lensed quasar, LBQS1009-0252, via new and relatively high-resolution data from the Gemini Multi-Object Spectrograph (GMOS) at Gemini Observatory. The project investigated both the emission and absorption lines present in the spectra of components A and B, seeking to better understand the spectral differences apparent between the two images. The analysis confirms that the LBQS1009-0252 system likely consists of two images of the same, gravitationally lensed background quasar source, with a third component, LBQS1009-0252C, most likely a foreground and physically unrelated quasar. A comparison and analysis of the overall spectra and emission lines attempts to separate the effects of different light paths through the lensing galaxy, previously identified at z~0.869. A combination of differential extinction due to dust in the macrolens plus a minor component of microlensing is a reasonable explanation for the origin of chromaticity between the spectra of the two component images. The new dataset was of high resolution, allowing for the identification of many more absorption lines than had previously been catalogued. These have been matched to those previously classified as belonging to the lensing galaxy and another known absorber situated at z~1.627. Newly-observed lines were analysed to identify likely absorption species candidates, showing that the presence of at least one more intervening absorption system at z~1.116–1.117 is highly likely.