Unveiling the physics of radio AGN feedback with LOFAR

One of the key ingredients of our models of how galaxies grow to the sizes they do is a 'feedback' process that stops the most massive galaxies from getting even bigger. In these galaxies, some of the matter that accretes onto the central supermassive black hole drives powerful jets of material that plough at high speed into the galaxy, heating the gas around them and stopping it from cooling and turning into stars. The jets are thought to act like a thermostat, switching on when the gas in the galaxy starts to cool and fall on to the black hole and heating it up again until it stops. We have observed these jets for many years in the form of 'radio galaxies' , characteristic double structures seen with radio telescopes around many massive galaxies.

We are conducting a survey of the northern sky with the LOFAR radio telescope which is by far the largest and most sensitive survey yet, and have identified hundreds of thousands of these radio galaxies and matched them up with the optical galaxy that generates the jet. What we want to do now is to understand whether this 'feedback' picture works in detail -- overall, is the thermostat working to maintain the temperature of the hot gas just right, or are there types of environment where it is more or less effective? And how does this change over the history of the universe? The data provided by the LOFAR survey can answer these questions, and our objective is to measure the properties of the radio galaxies we have found in great detail so as to get an understanding of how much energy each one is putting into its environment -- and what that environment is. Overall we will build up a picture of the way 'feedback' works, if it does, that will allow us to test our best computer models of the evolution of the universe.