Extended emission-line regions: Remnants of quasar superwinds

Abstract

Black holes are not only an integral component of galaxies, but they also appear to have played a fundamental role in galaxy evolution. It is theorized that galaxy-scale feedback from high-redshift quasars is key to understanding the properties of the most massive galaxies today. However, direct observations of the feedback have been lacking. Our observations on the extended nebulae around low-redshift quasars show that recent quasar-driven superwinds have drastically altered their environments. The superwind is capable of ejecting most of the interstellar medium to large distances, demonstrating an efficient mechanism that can regulate both star formation and black hole growth. Such superwinds provide local analogs of the quasar feedback hypothesized to have happened in the early universe. Studies of these objects can thus provide important insights into this key stage of galaxy evolution. It was discovered that quasars surrounded by extended nebulae are consuming low-metallicity gas. This finding not only provided the first direct observational evidence that the gas from a merger can indeed be driven to the feeding distance of the central black hole, but also validated the existence of low-metallicity quasars and placed a key constraint on quasar superwind models.