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About us Faculty of Science and Engineering PhD ceremonies

AGN relics in the radio sky

A LOFAR look into spectral aging and AGN duty cycles
PhD ceremony:Mr A. (Aleksandar) Shulevski
When:February 06, 2015
Supervisors:R. (Raffaella) Morganti, Prof, prof. dr. P.D. (Peter) Barthel
Where:Academy building RUG
Faculty:Science and Engineering
AGN relics in the radio sky

Galaxies have black holes in their nuclei: big galaxies host bigger while small galaxies host smaller black holes. These black holes grow during the lifetime of a galaxy (billions of years) through accretion of matter and they can end up being as massive as billions of suns put together. The accretion is not a steady process but occurs in episodes, each lasting tens of millions of years.

Certain types of galaxies produce strong radio waves during the accretion episodes. The radio emission can be detected for millions of years after the matter accretion episode of a black hole has ended, and it slowly fades as time passes. The observed structures, connected to galaxies which host previously active black holes are known as radio relics.

This thesis investigates radio relics by imaging their radio emission using the revolutionary Dutch built LOw Frequency ARray (LOFAR) radio telescope. We have used LOFAR to study several examples of radio relics and have derived the duration of the black hole accretion episodes as well as the time elapsed since the accretion has stopped. We have also made new relic discoveries, showcasing the promise which LOFAR holds for future work in this field of research.