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Title: Automated extraction of low surface brightness sources ; &, The physical nature of ultra-diffuse galaxies
Author: Prole, Daniel James
ISNI:       0000 0004 7973 0523
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2019
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As the size and depth of astronomical data improves, so must the software with which we use to extract sources from it. In this thesis, I describe a new software package, DeepScan, which I have written & designed to offer improvements over contemporary software packages such as SExtractor for detecting extended low surface brightness (LSB) features, particularly to avoid issues of excessive segment fragmentation. I demonstrate the technique by applying it over a 5 degree2 portion of the Next-Generation Virgo Survey data to reveal 53 LSB galaxies that are candidate cluster members based on their sizes and colours; 30 of which are new detections. The final sample have extremely low surface brightness (26.0 ≤ μ̅e ≤ 28.5) and low stellar masses (106.3±0.5M⊙), making them some of the faintest known dwarf galaxies in the Virgo Cluster. Improved detection and measurement techniques are crucial for identifying large samples of LSB galaxies, which are important for characterising the formation mechanisms of ultra-diffuse galaxies (UDGs): large, LSB galaxies with mysterious origins. In this thesis I have used the Kilo-Degree Survey together with the Hyper Suprime-Cam Subaru Strategic Program to measure the colours and abundances of UDGs in the field, where they are expected to form preferentially via secular mechanisms compared with those in denser environments. I show that a scenario in which cluster-like red sequence UDGs occupy a large fraction of field galaxies is unlikely, with most field UDGs being significantly bluer. I also estimate an upper-limit on the total field abundance of UDGs of 8±3 x 10⁻³cMPc⁻³ within my selection range; this is the first observational constraint on the total field abundance of UDGs. The implied mass formation efficiency of UDGs is high enough that I cannot rule out the possibility that secular formation mechanisms produce a significant proportion of UDGs.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QB Astronomy