Details in the structure of a distant quasar revealed

Using the German and Netherlands LOFAR telescope stations, astronomers have for the first time produced a high resolution image of a distant quasar at metre radio wavelengths.

Radio image of quasar 3C 196 at 4-10 metre wavelengths (30-80MHz frequency). Left: Data from the LOFAR stations in the Netherlands only. Right: Greater detail is revealed when the German stations are added to the array. Image: Olaf Wucknitz, Bonn University.

LOFAR, the LOw Frequency ARay telescope is an international European venture, with 44 stations located across the Netherlands, the UK, France, Germany and Sweden. Five stations in the Netherlands and three stations in Germany were connected and aimed at well-known quasar 3C 196. Quasars are the most luminous objects in the Universe and are found in the centres of massive galaxies, surrounding a central supermassive black hole.

“We chose this object for the first tests, because we know its structure very well from observations at shorter wavelengths,” says Olaf Wucknitz from the Argelander Institute of Astronomy (AIfA). “The goal was not to find something new but to see the same or similar structures also at very long wavelengths to confirm that the new instrument really works."

Observing with just the Netherlands' stations the astronomers saw only a fuzzy blob, but adding in the long baselines to observe at wavelengths between four and ten metres, intricate detail sprung into light.

The LOFAR station located in Bonn at the Max-Planck-Institut fuer Radioastronomie. Image: J. Anderson.

Observing the Universe at radio wavelengths is not a new concept, but the sensitivity of LOFAR will enable astronomers to see much fainter objects and to eek out their finer details. The resolution of telescope arrays like this depends on their physical separation; adding the stations located in the Netherlands to those in Germany alone improves the resolution by a factor of ten. The resolution will be further increased by a factor of four when observations at shorter wavelengths are added to the mix.

“The image quality of the final array depends crucially on the uniformity with which large areas are covered with stations”, says Anton Zensus, director at Max-Planck-Institut fuer Radioastronomie (MPIfR). “The German stations are already an indispensable contribution to the international array. What we are still lacking, however, is a station in northern Germany to close the gap between our stations and the ones of our Dutch friends. This would increase the image quality a lot.”