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ERC

RadioLife Report Summary

Project ID: 320745
Funded under: FP7-IDEAS-ERC
Country: Netherlands

Final Report Summary - RADIOLIFE (Exploiting new radio telescopes to understand the role of AGN in galaxy evolution)

The effect of the energy released by active galactic nuclei (AGN) is required by all cosmological simulations to reproduce the properties of the observed galaxies. Although we know that AGN can affect the surrounding medium, fully quantify this complex process is still an open issue.
Among the different type of AGN, radio galaxies stand out for their spectacular jets of radio plasma that can expand throughout and beyond the host galaxy: RadioLife ERC Advanced project has made use of the capabilities offered by the new generation radio telescopes to understand the impact that these radio jets can have.
RadioLife has explored the effects of radio jets in two complementary ways. Radio galaxies are known to be evolving objects, even if on time-scale well beyond the human one! They are born, grow older, die and they can also be re-born. RadioLife aimed at quantify this life-cycle, i.e. how often the radio-loud phase appears in the life of a galaxy, because the more often this cycle occurs, the more it affects the surrounding.
The second goal was to quantifying the impact of jets in different phase of evolution by deriving the occurrence and characterise massive gaseous outflows resulting from the impact of radio jets on the surrounding gas. To reach these two goals, the project has combined the challenges of innovative techniques used by of some of the new-generation radio telescopes (by developing analysis software and testing the products of the pipelines) with the science part.

The first main result of RadioLife is that, thanks to the new capabilities offered by LOFAR (Low Frequency Array, https://www.astron.nl/general/lofar/lofar) the project has provided a new view of the life-cycle of radio galaxies. The low frequencies, where even the older electrons can still shine long after the activity has switched off, have allowed us to trace the evolution of the radio plasma after the activity from the central super-massive black hole switch off.
The so-called “dying” radio galaxies could be identified by their morphology (low surface brightness, amorphous emission) thanks to the high quality of the LOFAR images. Surprisingly, we found that most of the dying sources observed are actually relatively young (a few x 10^7 yrs). We could compare these findings with models describing the evolution of radio galaxies and explain the observed fraction of dying sources as the result of a relatively rapid evolution of the radio source after the switching off combined with strong adiabatic losses. This has implications for the cycle of activity and, therefore, for the impact on the ISM.

The study of the gas (in particular HI and cold molecular) has confirmed, beyond any doubt, that radio jets can have a strong impact on the surrounding gas but has also shown that this impact is stronger when the source is young or newly restarted. Thanks to an HI absorption “pilot” survey, the largest available so far, done with the Westerbork Synthesis Radio Telescope (WSRT), we could derive that HI outflows (with velocities larger than 1000 km/s) are relatively common and, in particular, they are found in young or newly restarted radio galaxies. These outflows represent signatures of the impact of radio jets affecting the interstellar medium of the host galaxy.
The upcoming HI absorption surveys using APERTIF, the phase array feed upgrade to the Westerbork Synthesis Radio Telescope (https://www.astron.nl/general/apertif/apertif), will expand these results thanks to the greatly increase of the instantaneous field of view of this receiver. This instrument is now in the commissioning phase and the RadioLife team has help developing the imaging pipeline and tools for the analysis of the data have been developed.
Detailed follow-up observations of these fast outflows, reaching parsec-scale spatial resolution, have been done with ALMA (to trace the cold molecular gas) as well as with integral field spectroscopy in optical and IR (to trace the ionised and warm molecular gas) and using Very Long Baseline Interferometry to trace the HI. These observations have allowed, for the first time, detailed comparison with the results from numerical simulations of a jet entering a clumpy medium showing remarkable agreement.

In summary, the results from RadioLife have established that the effects of radio jets (even of low power) on the surrounding medium cannot be ignored and that the recurrent nature of the radio emission ensure that these effects occur multiple times in the life of a galaxy, thus supporting their relevance for feedback processes.

Reported by

STICHTING NEDERLANDSE WETENSCHAPPELIJK ONDERZOEK INSTITUTEN
Netherlands
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