A census of stellar structures in the Fornax cluster

Thesis event information

Date and time of the thesis defence

Place of the thesis defence

L6, Linnanmaa

Topic of the dissertation

A census of stellar structures in the Fornax cluster

Doctoral candidate

MSc Hung-Shuo Su

Faculty and unit

University of Oulu Graduate School, Faculty of Science, Space physics and astronomy research unit

Subject of study



Professor Sven De Rijcke, Ghent university


Docent Joachim Janz, University of Oulu

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A study of the morphological transformation of galaxies in the Fornax cluster

According to observations, galaxies in the Universe can be relatively isolated or reside in clusters bound by gravity. Those in higher density environments can experience interactions with other galaxies in the cluster or even with the cluster itself. In principle the interactions should affect the galaxies, such that there can be changes in the sizes and shapes of the galaxies, and sometimes even induce new structures, such as nuclear star clusters (NSC). Moreover, the population of stars in the galaxies can be affected, as the interactions can strip away the gas required to form new stars.

We have been working on accurately measuring and comparing the structures of galaxies to study how much the interactions can affect the galaxies, using the Fornax cluster as a laboratory. The dataset is based on very deep, multi-band optical images, which were taken with the wide-field telescope instrument OmegaCAM from ESO (European Southern Observatory). We find that galaxies in the cluster show significantly different features than those outside of the cluster, with evidence which suggest that cluster galaxies tend to become more extended, more symmetric, and host on average older stars than those outside the cluster. Still, we find that the likelihood of a galaxy exhibiting complex structures is mainly driven by its stellar mass, rather than the environment it resides in.

After disks, NSCs are one of the most common structures found in galaxies. A NSC is a compact cluster of stars at the centre of a galaxy. We find that the presence of NSCs depends on both the host galaxy mass and its environment, whereas the NSC properties are correlated with the galaxy mass. We also develop a method which can detect NSCs in galaxies in an unsupervised manner, with applications for the large datasets from next-generation telescopes.

This thesis was a part of the SUrvey Network for Deep Image Analysis and Learning (SUNDIAL), an Horizon2020 Innovative Training Network consisting of nine astronomy and computer science institutes across Europe.
Last updated: 23.1.2024