I am generally interested in the structure and evolution of galaxies. As such a large part of my research focusses on the distrubution and kinematics of hydrogen in spiral galaxies. As such my research is dominated by observations of HI, neutral hydrogen line emission at radio wavelengths, and Hα, ionized hydrogen line emission at optical wavelengths. However, to understand the full flow of the gas in galaxies we also need to look at other components of spiral galaxies such as the stars, star formation and the molecular gas and therefore I always try to combine observations at several different wavelengths in my research.

With the advance of large all sky surveys it becomes important to be able to analyse most datasets in a automated manner. In the analysis of neutral hydrogen the tilted ring model is a common tool to use to retrieve the kinematical parameters. However, this process is still largely manual and subjective. I have therefore also developed an interest in, and started developing, codes that can automatically fit these models to HI data cubes

The sections below describe in more detail the various fields that my research currently focusses on

The haloes of spiral galaxies connect their inner disks to the inter galactic medium. Additionally they can serve as reservoirs of baryonic matter that can replenish the the star forming gas in the discs of galaxies. However, these haloes are very hot with cooling times similar to a Hubble time. Recent modelling shows that the cold gas in the halo, expelled by star formation in the disc, can serve as an catalyser in cooling down the hot halo. This makes the disc-halo connection a crucial element in understanding galaxy evolution and the continued star formation in spiral galaxies. As part of the HALOGAS Team I have investigated several spiral galaxies for the existence of HI thick disks. One very detailed study focussed on NGC 5023 and UGC 2082 and is published in MNRAS . In paper we show that non-cylindrical HI distributions can have a significant effect on the determination of the lag in edge-on galaxies.

Currently my research in this field focusses on expanding the type of galaxy that is observed to have HI thick disks. Up to now research in this field has focussed on spiral galaxies, in which extra-planar cold gas has been observed regularly. However, in the last decade it has become clear that many Early Type Galaxies (ETGs) also contain significant fractions of HI as well as star formation. As the star formation history of ETGs is significantly different from spiral galaxies they provide an excellent opportunity to study the disc-halo connection from a completely new angle. One such ETG, ESO 92-G021, has been found to have a comparatively high rate of star formation and an extended, regular HI disk. In order to study whether this galaxy contains extra-planar neutral hydrogen we have obtained deep observations with the Australia Telescope Compact Array.

For many decades neutral hydrogen has been the key element used to study the dynamics of nearby galaxies. Due to its ubiquity in galaxies as well as the fact that its ground state emits at radio frequencies, the Doppler shifts of the gas are easily measurable over large parts of galaxies. To ease the analysis of neutral hydrogen observations, models consisting of circular rings that can tilt with respect to each other have been fitted to the data for several decades now. This kind of modelling has been mainly used for the extraction of rotation curves, which provide one of the first and strongests indications for the existence of dark matter, from the data. However, the construction of such models has always required a significant amount of human interaction and errors are ill understood, hence creating them is a subjective process.

With the coming completion of ASKAP in Australia and APERTIF in the Netherlands, large surveys of neutral hydrogen are planned for the near future. The all sky survey WALLABY is expected to resolve thousands of galaxies such that their kinematics can be extracted from the data. This would require fully automated fitting of the models. In order to explore the requirement for such autometed fitting I have developed the Fully Automated TiRiFiC (FAT). Currently the focus of development is to make a GDL version of FAT that produces as good or better models than the already released IDL version.