The dust doesn’t settle in merger galaxy II Zw 096

Licentiate thesis, 2025

Understanding galaxy formation and evolution is one of the central goals of modern astronomy. Investigating the life cycle and properties of the components within galaxies can provide valuable insights into these processes. The interstellar medium consists of gas and dust, with the latter being 1% of the interstellar medium by mass. However, cosmic dust grains, which are small solid particles, significantly affect physical and chemical processes and thus play an important role in galaxy evolution. Previous studies of dust have shown how the physical environment triggers a variation in dust properties such as size distribution and grain composition. These properties can be traced by observing emission from stochastically heated nanograins in the mid-infrared using observatories such as the James Webb Space Telescope (JWST).

This thesis provides a summary of how dust properties, with a focus on nanograins, vary and how they link to galaxy evolution in our nearby Universe, in particular in the dusty (Ultra-)Luminous InfraRed Galaxies (LIRGs and ULIRGs). Also described is the workings of JWST and the spectral decomposition tool CAFE (Continuum And Feature Extraction tool) used in the analysis in the included paper.

Using JWST Near Infrared Spectrograph (NIRSpec) and Mid-InfraRed Instrument (MIRI) spectroscopic data from nearby LIRG II Zw 096 it could be concluded that the average dust grain size vary across the field of view. The ratio of aromatic (ring structured carbon chains) to aliphatic (open carbon chains) compounds in the dust grains was also shown to vary, though to a lesser extent. A larger average dust grain size was observed towards more extreme environments such as towards a proposed obscured AGN. This is also where the aliphatic compounds seem to be more efficiently destroyed.

The thesis provide new insights on how dust properties vary with the environment where it is found, in particular in the extreme environments in LIRGs. Further investigation of how dust properties vary in the most extreme environments in our Universe, the Compact Obscured Nuclei (CON) is of high importance to further understand galaxy evolution and how dust fit into the puzzle. Such targets include IC 860 and NGC 4418, which are of focus for future work.