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AGN are episodic in nature, cycling through periods of activity and quiescence. Their life-cycle is key for understanding the impact they have on their host galaxy. In this talk, I will present our studies aimed at understanding the life-cycle and the role of the gas in a particular class of active nuclei: the radio-loud AGN. These studies make use of the exciting possibilities offered by the new generation of radio telescopes. For radio AGN, their evolutionary stage (young, adult, dying, restarted) can be derived from the radio spectra and morphology, in particular by using the capabilities of new low-frequencies radio telescopes. Our search of dying and restarted sources aims at understanding the time-scale of their evolution. The study of their duty-cycle has been done in the MHz-domain using the LOFAR radio telescope and the continuum surveys that are now in progress. I will summarise the results and compare them with evolutionary models of radio sources developed by our group. In the second part of the talk, I will present the results of our study on the effect of the radio plasma on the surrounding medium. Surprisingly, and despite the extremely energetic phenomena, these effects can be traced by the cold component of the gas using the atomic HI-21cm and the molecular (CO) components. I will describe the presence and characteristics of these fast and massive outflows and discuss the important connection between the evolutionary stage of the radio source and the effect of the radio plasma on the surrounding ISM. The results presented represent and important starting point for the large surveys (in particular of HI absorption) that are about to start with SKA pathfinders and, in the near future, with SKA. |
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