Discovery Magazine

The Importance Warm Outflows in the Most Rapidly Evolving Galaxies in the Local Universe

Energetic, galaxy scale outflows powered by their central active galactic nuclei are increasingly recognized as a key element in the overall galaxy formation and evolution processes, regulating the correlations between the masses of the central supermassive black holes and host galaxy properties, and influencing the luminosity functions of galaxies, particularly at the high luminosity end. These outflows can take two main forms. First, relativistic jets ejected by radio-loud active galactic nuclei. Second, winds driven by active galactic nuclei in the heart of many galaxies. Although it is now well established that the relativistic jets have a major effect on the cooling of the hot intergalactic and intercluster medium on the scales of galaxy haloes and clusters, there remains considerable uncertainty about the significance of the active galactic nuclei wind mode of feedback.

Combined with information derived from existing ground-based spectra, Hubble Space Telescope data is being used to quantify the mass outflow rates and kinetic powers of the warm outflows for the first time in a significant sample of nearby ultra-luminous infrared galaxies (ULIRGs). In this way we will establish whether the warm, active galactic nuclei-driven outflows (as opposed to relativistic jets) are energetically important and a major factor in the evolution of the host galaxies. Given that the ULIRGs represent low redshift analogues of the rapidly evolving galaxies with relativistic jets now routinely detected in surveys of the distant Universe, the results will be important for our understanding of the co-evolution of supermassive black holes and their host galaxies at all redshifts.