Radial Inflows in Nearby Spiral Galaxies
During my Master's thesis, I worked with Frank Bigiel at the Institute for Theoretical Astrophysics (University of Heidelberg) on the kinematics of neutral HI gas in nearby spiral galaxies. I used 21cm radio observations from the THINGS survey and a custom-developed tilted-ring model to search for radial inflows in the discs which could transport gas from the circumgalactic medium to the inner part of the galaxies and fuel star formation.
The Helium II Transverse Proximity Effect
Quasars are extremely luminous sources of ionizing photons and in particular the only population of objects that produce in large quantities photons with energies > 54 eV, required to doubly-ionize helium. Therefore, quasars have a strong impact on the ionization state of the intergalactic medium in their surrounding. Detailed studies of the HeII Lya forest absorption along background sightlines that pass close to foreground quasars can therefore reveal detailed information about the process of cosmic HeII reionization but even more about the emission properties of quasars. For most of my Ph.D. I have worked on this so called 'HeII Transverse Proximity Effect', by conducting a dedicated foreground quasar survey around existing HeII sightlines, compared to and developed a detailed modeling of the transverse proximity effect to put constrains on the lifetime and obscuration of quasars.
Mapping Quasar Light Echos in 3D with Lyα Forest Tomography
Studies of the HeII Lyα forest require Far UV spectroscopy, for instance with HST/COS. Since its capabilities are nearly exploited and the next generation of space-based UV telescopes will become available only decades from now, I currently work on the HI proximity effect. The quasar proximity effect in hydrogen is for several reasons much weaker than in helium. However, it can be observed from the ground with powerful optical telescopes. This allows to employ a technique called 'Lya forest tomography'. For this, one observes a relatively large number of background sources (typically faint galaxies) that probe the proximity region of a foreground quasar. This can give a very detailed and unambiguous picture of the emission geometry and emission history of the foreground quasar by basically mapping its 'light echo' in three dimensions.