Mid-infrared imaging of dust in galaxies

PhD ceremony: Mr. G. van der Wolk, 16.15 uur, Aula Academiegebouw, Broerstraat 5, Groningen

Disseration: Mid-infrared imaging of dust in galaxies

Promotor(s): prof. P.D. Barthel, prof. R.F. Peletier

Faculty: Mathematics and Natural Sciences

Galaxies are the building blocks of the universe. Their main components are stars, dust and gas clouds. Many dust and gas clouds harbour newly formed stars. Supermassive black holes can be found in the nuclei of almost all galaxies. A small fraction of galaxies have a very bright nucleus, a so-called active galactic nucleus (AGN), within some cases an energy output that exceeds the amount of radiation from all the stars in the galaxy. This energy is believed to arise from the accretion of matter onto the supermassive black hole.

In this thesis images of early-type spiral galaxies and the nuclei of radio galaxies are analyzed. The images, from ESO's Very Large Telescope, and from the Spitzer Space Telescope, have been taken in the mid-infrared, a wavelength region that only recently has become available due to new detector-developments. This thesis shows that the mid-infrared provides an excellent method to study the stellar populations and star formation across galaxies and the accretion activity of their central supermassive black holes.

Conclusions that follow from this work are: (i) The central regions of early-type spiral galaxies show a large range of star formation rates and modes. (ii) Using a combination of mid-infrared colours one can detecting active galactic nuclei with a low accretion efficiency very efficently. (iii) Infrared images can be used very well to study the nature of the nuclear activity in the active galactic nuclei of radio galaxies.