Major Galaxy Mergers and the Growth of Supermassive Black Holes in Quasars

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Science  25 Mar 2010:
DOI: 10.1126/science.1184246


Despite observed strong correlations between central supermassive black holes (SMBHs) and star-formation in galactic nuclei, uncertainties exist in our understanding of their coupling. We present observations of the ratio of heavily obscured to unobscured quasars as a function of cosmic epoch up to z ≅ 3, and show that a simple physical model describing mergers of massive, gas-rich galaxies matches these observations. In the context of this model, every obscured and unobscured quasar represents two distinct phases that result from a massive galaxy merger event. Much of the mass growth of the SMBH occurs during the heavily obscured phase. These observations provide additional evidence for a causal link between gas-rich galaxy mergers, accretion onto the nuclear SMBH, and coeval star formation.