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Understanding the extreme classes of dwarf galaxies

PhD ceremony:T. (Teymoor) Saifollahi, PhD
When:March 22, 2022
Supervisors:prof. dr. R.F. (Reynier) Peletier, prof. dr. E.A. (Edwin A.) Valentijn, prof. dr. J.H. Knapen
Where:Academy building RUG
Faculty:Science and Engineering
Understanding the extreme classes of dwarf galaxies

Evidence shows that more than eighty per,cent of the matter in the Universe is in the form of dark matter which does not interact with ordinary matter (like stars and gas in galaxies, also called baryonic matter) except through gravitation. This means that dark matter does not produce any observable light. Dark matter makes up most of the matter within galaxies and other main components of galaxies, stars and neutral gas, have a smaller contribution to the total mass of galaxies. The amount of dark matter compared to stars and gas is known to vary between galaxies. Massive galaxies like the Milky way have 10 times more dark matter than their stars and gas combined while this value increases to 100-1,000 for lower mass galaxies, generally called "dwarf galaxies". This implies that the key to understand the nature of dark matter ties in with dwarf galaxies, the most dark matter dominated objects in the Universe. Therefore, to solve the mystery of dark matter, we need to gain a deeper knowledge of dwarf galaxies.

Most of the research on dwarf galaxies in the past has focused on the detailed properties of nearby systems or the most commonly occurring types of dwarfs. Alternatively, exceptional insight into these objects is gained through studying the most extreme examples. Therefore, this PhD research focuses on two extreme classes of dwarf galaxies, ultra-diffuse galaxies (UDGs) and ultra-compact dwarf galaxies (UCDs); UDGs as the most diffuse and UCDs as the most compact classes of dwarf galaxies. These two classes have raised several issues and open questions in the last years which challenge our understanding of dwarf galaxies, dark matter and in general, galaxy formation and evolution.