The Coevolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe

Abstract

We summarize what large surveys of the contemporary Universe have taught us about the physics and phenomenology of the processes that link the formation and evolution of galaxies with their central supermassive black holes. We present a picture in which the population of active galactic nuclei (AGNs) can be divided into two distinct populations. The radiative-mode AGNs are associated with black holes (BHs) that produce radiant energy powered by accretion at rates in excess of ∼1% of the Eddington limit. They are primarily associated with less massive BHs growing in high-density pseudobulges at a rate sufficient to produce the total mass budget in these BHs in ∼10 Gyr. The circumnuclear environment contains high-density cold gas and associated star formation. Major mergers are not the primary mechanism for transporting this gas inward; secular processes appear dominant. Stellar feedback is generic in these objects, and strong AGN feedback is seen only in the most powerful AGNs. In jet-mode AGNs the bulk of energetic output takes the form of collimated outflows (jets). These AGNs are associated with the more massive BHs in more massive (classical) bulges and elliptical galaxies. Neither the accretion onto these BHs nor star formation in their host bulge is significant today. These AGNs are probably fueled by the accretion of slowly cooling hot gas that is limited by the feedback/heating provided by AGN radio sources. Surveys of the high-redshift Universe paint a similar picture. Noting that the volume-averaged ratio of star formation to BH growth has remained broadly constant over the past 10 Gyrs, we argue that the processes that linked the cosmic evolution of galaxies and BHs are still at play today.