Oral Abstract

Oral Contribution (O0.2) Nika Jurlin (Kapteyn Institute)

Life cycle of radio galaxies

Supermassive black holes at the centre of galaxies can cycle through periods of activity (in this phaseknown as active galactic nuclei, AGN) and quiescence. Quantifying the duty cycle of AGN is crucial forunderstanding the energetic impact they have on the host galaxy. In radio AGN this duty cycle can beinvestigated by using the characteristics of the radio spectrum and the morphology of the radio emission.The low radio frequencies can be used as a fossil record to trace the oldest populations of particles.Newly available surveys at low frequencies, such as the ones obtained by LOFAR and GMRT allow us todetect sources in the most elusive phases (dying and restarting) in greater numbers than it was possibleso far. Therefore, we can finally better characterise these phases, understand their occurrence and theirrole in the life cycle of radio galaxies. We have used deep LOFAR images, together with the higherfrequency surveys of the Lockman Hole extragalactic field to select a sample of objects in the dying andrestarting phases of this cycle. In this talk, I will present a VLA follow-up study at a higher frequency of23 candidate remnant radio galaxies initially selected by Brienza+17, to better characterise their radioproperties and confirm their remnant nature. I will also present a sample of candidate restarted radiogalaxies that we selected in the same field using criteria based on the core prominence and the spectralindex. I will discuss and compare the radio and optical properties of remnant, restarted and active radiogalaxies used as a comparison sample. I will discuss their rate of occurrence, which providesfundamental information for understanding the duty cycle of radio sources. The results will also bediscussed in the context of models of the evolution of the radio sources that we have developed in orderto obtain a broader understanding of the life-cycle of radio galaxies. The methods for the identification ofrestarted radio sources and optical identification of both remnant and restarted radio sources developedfor this project will soon be applied for selecting larger samples in the LOFAR Two-metre Sky Survey.