The life cycle of radio galaxies as seen by LOFAR

This Ph.D thesis presents an investigation of the various evolutionary phases observed in radio galaxies. What makes these galaxies peculiar is the presence of a supermassive black hole at their centre that attracts the surrounding gas under the influence of its huge force of gravity. During this process twin jets of energetic particles are produced, which expand throughout the host galaxy and beyond and emit most of their energy at radio frequencies. These jets are intermittent and, since they can have a substantial impact on the host galaxy, studying their evolution and the timescales of their activity is crucial to understand the overall galaxy evolution process.

In particular, in this thesis we have studied the properties and evolution of remnant and restarted radio galaxies, which represent the phases when the jets switch off or restart, respectively. For this project we have made an extensive use of the LOw Frequency ARray (LOFAR), which is a new generation radio telescope based in the Netherlands that observes the sky at frequencies below 250 MHz. Observations at MHz frequencies are indeed ideal to study the oldest emission produced by the jets of remnant and restarted radio galaxies during their past phase of activity. Therefore, they allow us to reconstruct the evolution of radio galaxies over a broad timescale.

Dissertation: http://hdl.handle.net/11370/07f51df8-4ee0-4c6a-8527-0f89f69aae32