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  • 2022chanphd

    Final published version, 21.5 MB, PDF document

    Available under license: CC BY: Creative Commons Attribution 4.0 International License

  • 2022chanphdchapter3supplementary

    Final published version, 10.6 MB, PDF document

    Available under license: CC BY: Creative Commons Attribution 4.0 International License

  • 2022chanphdchapter4supplementary

    Final published version, 1 MB, PDF document

    Available under license: CC BY: Creative Commons Attribution 4.0 International License

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Galaxy Cluster Detection and Characterisation in the Big Data Era

Research output: ThesisDoctoral Thesis

Published
Publication date15/08/2022
Number of pages245
QualificationPhD
Awarding Institution
Supervisors/Advisors
Award date19/07/2022
Publisher
  • Lancaster University
<mark>Original language</mark>English

Abstract

In this thesis, we present proof-of-concept studies that describe how data-driven techniques can be applied to observational data in order to detect and estimate properties of galaxy clusters, which are the largest gravitationally bound objects to have assembled in the Universe. Given the significance of clusters in astrophysics and cosmology, it is important to develop automated methods that are able to efficiently detect and process a large sample of clusters from existing photometric datasets, in preparation for upcoming large-scale galaxy surveys. This can be achieved by employing machine learning algorithms that are suited at solving the tasks at hand. In particular, algorithms that can self-learn the importance of features from the labelled data of known clusters, which minimises the amount of manual input required to make accurate predictions.

Initially, we demonstrate how a popular object detection algorithm can be applied to wide-field colour images to identify and predict the astronomical coordinates of clusters. We then demonstrate how a novel ensemble regression algorithm can be applied to line-of-sight galaxies within colour-magnitude space to estimate the photometric redshift of clusters. Finally, we present a hybrid empirical and analytical model that performs background subtraction of field galaxies along the line-of-sight of clusters within colour-magnitude space and then estimates the richness of clusters within a characteristic radius.

We also compare our findings with the results of existing conventional techniques to examine the overall predictive performance of our methods at generalising to unseen instances. Furthermore, we note that our methods can be combined together into a sequential data pipeline to create a comprehensive catalogue that contains key characteristics (e.g. position, distance, mass) of observed clusters for conducting astrophysical and cosmological research.

Bibliographic note

2022chanphdchapter3supplementary.pdf and 2022chanphdchapter4supplementary.pdf are supplementary appendices files to accompany the main thesis.