Coffee talks
Friday 18/01/2019 @ 11:00, Sala riunioni quarto piano
Nika Jurlin (Kapteyn Astronomical Institute), "Dying and restarting phase of the life-cycle of radio galaxies"
Supermassive black holes at the centre of galaxies can cycle through periods of activity (in this phase known as active galactic nuclei, AGN) and quiescence. Quantifying the duty cycle of AGN is crucial for understanding the energetic impact they have on the host galaxy. In radio AGN this duty cycle can be investigated by using the characteristics of the radio spectrum and the morphology of the radio emission. The low radio frequencies can be used as fossil record to trace the oldest populations of particles. We have used deep LOFAR images of the Lockman Hole extragalactic field to select a sample of objects in the dying and restarting phases of this cycle. In this talk, I will present a follow-up study at a higher frequency of 23 candidate remnant radio galaxies initially selected by Brienza+17, to better characterise their radio properties. I will also present a sample of candidate restarted radio galaxies that we selected in the same field using criteria based on the core prominence and the spectral index. I will discuss the radio properties of remnant and restarted radio galaxies and the optical properties of the respective host galaxies, as well as their rate of occurrence, which provides fundamental information for understanding the duty cycle of radio sources. The results will be discussed in the context of models of the evolution of the radio sources.