I am a staff astronomer at the observatory of Leiden University and work on ELT/METIS and VLTI/MATISSE.

My main research interest is in the nuclear regions of active galaxies (Active Galactic Nuclei, AGNs) which I study using very high spatial resolution techniques, such as infrared interferometry and adaptive optics, and with spectroscopy.

AGNs are thought to play a major role in transforming galaxies from gas-rich spiral galaxies to the so called ‘red and dead’ ellipticals, at least in the most luminous galaxies. There is some agreement that ‘AGN feedback’ is important in this transformation as it could push out the molecular gas out of which stars form. However, clear observational evidence for this outflow is very hard to collect, especially at high redshift where this ‘co-evolution’ mostly occurs. In ‘local’ AGNs cosmic evolution does not play a role, but the physical processes in the nuclei can actually be resolved and studied in detail. It is my hope and my ambition that the insights we gain from resolved studies of the AGN phenomenon in the local universe will ultimately provide us with a better understanding of the global evolution of galaxies from the early universe until now.

Recent research highlights

coverpage_scanIn a large study, using archival VLT/SINFONI IFU data of over 50 local AGNs, we dissect the nuclear near-infrared continuum into AGN light and starlight, using the stellar CO absorption band heads as tracers of the stellar population. Maps of this stellar feature (actually its equivalent width) are shown in the collage to the left. This allows us not only to build new very high resolution luminosity relations for AGN cores (useful e.g. to calibrate SED models for AGNs), but we also interpret the different infrared colors of AGNs in terms of a simple AGN torus model. This model consists of only two simple components — warm and hot dust –, but is able to explain the SED and spectral slope from the near to the mid-IR very well.We have also used this model — and its derived values of e.g. extinction towards the nuclear engine — to understand the relation between dust extinction and X-ray absorption in AGNs.


ism_spp_lowresIn other news, I am happy to announce that my project “Towards a comprehensive understanding of the interstellar medium in the extreme environment of Active Galactic Nuclei” has been selected to be funded in the DFG priority programme 1573 “The Physics of the interstellar medium”. In this project I will be using VLT/SINFONI and VLT/X-SHOOTER data to analyze the star formation histories of a well-defined sample of local luminous AGNs as well as matched sample of inactive galaxies.

My Tweets