/library/oar/handle/123456789/112403 2025-11-04T21:49:47Z 2025-11-04T21:49:47Z /library/oar/handle/123456789/135048 2025-06-18T07:40:08Z 2023-01-01T00:00:00Z

Title: Rationalising marine space : a multidisciplinary analysis for ecosystem-based marine spatial planning Abstract: This work and its abstract are both under embargo until the restriction is lifted. Description: Ph.D.(Melit.)

2023-01-01T00:00:00Z /library/oar/handle/123456789/131234 2025-01-29T11:12:00Z 2023-01-01T00:00:00Z

Title: The night sky brightness of Malta Abstract: Light pollution is the harmful increase in lighting at night as a result of ill-directed and uncontrolled artificial light. In the Maltese Islands, the amount of artificial light at night has significantly increased in the last few years, largely due to unregulated light emissions. The motivation to continue monitoring and quantifying the geographical pattern of the light pollution problem in Malta stems from its adverse effects on numerous fields, including astronomical observation, ecology and human health. In this study, Malta was mapped onto a 1 km2 grid and its light pollution levels were investigated by measuring the night sky brightness in each square using a Unihedron Sky Quality Meter (SQM). It was found that a previously used SQM exhibited a drift due to ageing, so all its measurements were reassessed using a brand new SQM. Analysis on this drift was carried out which showed an apparent trend towards darker skies. With the help of coloured grids and interpolation maps, the general distribution of light pollution in Malta was analysed. The north and west parts of Malta remain dark while the central, east and south areas are severely polluted. Overall, Sliema, Valletta, Marsa, and Birzebbuga, were found to be the most light polluted regions in Malta. Furthermore, the collected data was directly compared to a similar study done in 2017/18 to investigate the change in light pollution levels. Approximately 42% of the areas were found to be brighter in this research, despite the 2017/18 study not adopting an anti-glare hood to block out neighbouring lights. This study brings to the fore the extent of light pollution in Malta, and the importance to regulate its light emissions. Future studies are encouraged to adopt this methodology once again to further identify any new hotspots and problematic areas in Malta and to preserve the few remaining dark skies in our islands. Description: B.Sc. (Hons)(Melit.)

2023-01-01T00:00:00Z /library/oar/handle/123456789/131127 2025-01-27T14:13:44Z 2023-01-01T00:00:00Z

Title: The stellar populations trapped at the L4/L5 Lagrange (corotation) points of a bar Abstract: Bars are prevalent features in disc galaxies and play an important role in driving secular evolution. One important effect of bars is resonances. Stars at corotation resonance with the bar are known to librate around the stable Lagrange points (L4, L5). Here, we investigate the orbits and properties of corotating stars as well as the effects of bar weakening on the corotation resonance. By performing an orbital frequency analysis on a subsample of stars in an N-body+SPH simulation of an isolated, barred galaxy, at two distinct times at which the bar has different strengths, we obtain corotating and non-corotating subsamples. The results at both times are compared numerically to evaluate the consequences of bar weakening. A selection of stellar orbits are plotted over a short timespan to investigate the different trajectories followed by corotating and non-corotating stars. Trends in rform, age, and metallicity are systematically investigated by sectioning the galactic plane into radial and azimuthal bins, and comparing the properties of both categories of stars within each bin, using a K-S test to check statistical significance. We confirm the existence of important systematic differences between the distributions of the radii of formation, ages, and metallicities of the corotating stars with respect to the surrounding non-corotating stars. Trends in rform and age are found to vary radially and suggest that corotating stars are dragged away from the corotation radius in both directions, whereas the metallicities of stars in corotation are found to be distinctly higher. We find that bar weakening largely disrupts these trends, by diminishing the bar’s ability to retain captured stars or trap new stars at corotation. We also show that stars at corotation may be trapped only temporarily and escape before following a well-defined orbit around the Lagrange points, which implies that tracking their trajectories is not a suitable way of identifying corotating stars. Description: B.Sc. (Hons)(Melit.)

2023-01-01T00:00:00Z /library/oar/handle/123456789/131125 2025-01-27T14:12:01Z 2023-01-01T00:00:00Z

Title: The TNG50 view of type III breaks in disc galaxies Abstract: The outskirts of disc galaxies are known to contain vital information about the formation and evolution of such galaxies. In this dissertation, we use the TNG50 magnetohydrodynamical (MHD) simulation to study the radial density profiles of disc galaxies. We find that at z = 0, most of the galaxies (∼ 40%) are found to have Type III (up-bending) density profiles, whilst only a small fraction of disc galaxies (∼ 10%) were found to have Type II (down-bending) density profiles. This continues to show how Type II profiles tend to disappear in the mass density profile. Moreover, we find that although bars do not seem to influence the type of break, they do influence the location of the break radius, with barred galaxies having a larger Rbreak/Reff than unbarred galaxies. We also find that ∼ 30% of Type III breaks are associated with the nearly spherical stellar halo. We attribute mergers as being the formation mechanisms for the intrinsic Type III breaks. Description: B.Sc. (Hons)(Melit.)

2023-01-01T00:00:00Z