Gravitational lensing is observed when light from a star or galaxy is deflected by the gravity of a massive object, typically a galaxy or cluster of galaxies. When that object is positioned on the line of sight between us and the light source, the phenomenon produces multiple images of the background object that are both distorted and magnified. The main research goal of the gravitational lensing group at ASTRON is to investigate the distribution of matter (luminous and dark) in distant galaxies and to probe the high redshift Universe through the use of lenses as natural telescopes.
Mass distributions of galaxies
Using the effect of gravitational lensing, we can study the mass distributions of galaxies over cosmic times. We can infer the density of mass and the clumpiness of dark matter in the lensing galaxies by looking at the positions of the lensed objects. The group at ASTRON is focused on studying systems where the background galaxy shows strong radio emission from an AGN and/or star-formation activity. This allows the lensed emission to be measured without any contamination from the lens, which is often radio-faint.
At radio wavelengths, we use the European VLBI Network (EVN) and the Very Long Baseline Array (VLBA). Complementary observations are also carried out at optical and infrared wavelengths with the HST, VLT and Keck telescopes.
Star-forming galaxies at high redshift
We also use the magnification provided by gravitational lenses to study distant star-forming galaxies and active galaxies at high redshift. The magnification allows us to observe the structure of really fainter star-forming galaxies that would have otherwise not been observable. Radio observations are particularly well suited to study star-forming galaxies because they
- do not suffer from dust extinction
- have sufficient angular resolution so that the star-forming galaxy can be identified
- have the sensitivity to probe the less extreme starbursts.
We combine radio observations with the VLA and WRST with data of the heated dust and molecular gas at high frequency to understand feedback processes in these galaxies and test galaxy formation models.
Next generation lens surveys
As we increase the number of detected gravitational lenses, we get a better picture of how galaxies and dark matter evolve over different epochs. Our group at ASTRON is also focused on searches for new lenses with LOFAR and the Very Long Baseline Array in preparation for the tens of thousands of lenses that will be found with the Square Kilometre Array. We test algorithms to find large samples of lenses with LOFAR. We also develop methods to increase the angular resolution of our images and improve our detection by using LOFAR stations available in other countries.