In this thesis we provide a better understanding of the role of the inter-cluster filamentary environment in the evolution of galaxy properties, relating that to the physical mechanisms involved. We examine a poorer supercluster structure and describe how it compares with the richer regime, deciding whether the same processes are responsible for driving galaxy evolution in both cases. We develop a new approach to automated galaxy morphology classification, undertake an extensive observational survey of a nearby supercluster and investigate the evolution of galaxy properties within this structure, considering the filamentary environments that we confirm exist. Firstly, we present an application of Mathematical Morphology (MM) for the classification of astronomical objects, both for star/galaxy differentiation and galaxy morphology classification. We demonstrate that, for CCD images, 99.3 ± 3.8% of galaxies can be separated from stars using MM, with 19.4±7.9% of the stars being misclassified. We demonstrate that, for photographic plate images, the number of galaxies correctly separated from the stars can be increased using our MM diffraction spike tool, which allows 51.0±6.0% of the high-brightness galaxies that are inseparable in current techniques to be correctly classified, with only 1.4 ± 0.5% of the high-brightness stars contaminating the population. We demonstrate that elliptical (E) and late-type spiral (Sc-Sd) galaxies can be classified using MM at an accuracy of 91.4 ± 7.8%. It is a method involving less ‘free parameters’ than current techniques, especially automated machine learning algorithms. The limitations of MM due to seeing and distance are also discussed. We examine various star/galaxy differentiation and galaxy morhpology classification techniques commonly used today, and show that the above MM techniques compare very favourably. Secondly, we present a wide-field photometric and spectroscopic study of the supercluster SCL266 (z = 0.068). We have obtained CCD imaging in B-, R- and I-bands covering 5 clusters within the structure, and spectroscopy within the region of 3 of the clusters and the filamentary environment between them. We have over 950 redshifts obtained and 161 galaxies confirmed as members of the supercluster structure. The galaxy morphologies are derived using the MM techniques we have developed. We show that the population of passive, early-type galaxies extends into the dense regions of the filaments and is not just confined to the higher-density clusters, indicating that the denser filamentary environment hastens the galaxy evolution within it. The star-forming, late-type galaxies are distributed throughout the entirety of the supercluster structure. We show that both the mean star formation rate and the fraction of star-forming galaxies decrease strongly as a function of distance along the filaments towards the cluster centres. Given these observations we conclude that the evolution occurring within this poor supercluster begins within the filaments up to 4 Mpc away from the cluster centres, and is driven by long time-scale mechanisms involving encounters between neighbouring galaxies.
| Identifer | oai:union.ndltd.org:ADTP/254128 |
| Creators | Jason A. Moore |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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