Speaker: Joe Silk (Oxford and Paris)
I will review our understanding of feedback, on scales from stars to galaxies. I will focus on massive spheroids, where one invariably finds evidence for the presence of supermassive black holes. These are often visible, especially at early epochs, as active galactic nuclei. Negative feedback, from the central black hole during its accretion phase, quenches the gas supply to the spheroid and thereby suppresses star formation. We also observe enhanced star formation at early epochs. This may provide evidence for positive AGN feedback. I will review the various theoretical and observational implications of the AGN-star formation connection.