Cosmic telescopes: witnessing the radio quiet quasar emission mechanism

The quasar model has reached relative maturity: we know that light is emitted at great power across the electromagnetic spectrum from the active nuclei of distant galaxies, where violent accretion processes release huge amounts of energy from gravitational stores. We observe that, in some quasars, matter falling onto the central black hole is funnneled into dramatic jets, emitting radio light across galactic distances. Over cosmic history the quasar population peaked in unison with star formation activity, leading us to suspect the role of quasars in the quenching of star-formation. Missing from the picture, however, is a full understanding of how such feedback processes manifest in the vast majority of quasars: those objects with very little radio emission. In these 'radio-quiet' quasars, jets appear to be absent, and it is possible that the faint radio signal that we do detect is the result either of smaller-scale AGN activity, of continued star formation, or of both. Only by undestanding the source of this very faint emission can we fully understand the quasar stage of galaxy evolution. This talk presents findings using strong gravitational lenses as 'cosmic telescopes' that magnify distant source structure, allowing us to resolve these intriguing objects to the sub-parsec scale.