Signatures of Supermassive Black Hole Mergers: Before and After

Laura Blecha

October 20, 2011

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Abstract: Supermassive black hole (SMBH) pairs are expected to form in major galaxy mergers. However, until recently, only a few such objects were known, and even less is known empirically about their subsequent evolution to a BH merger and gravitational-wave recoil kick. I will review the remarkable recent progress in identifying candidate SMBH pairs, as well as recent identifications of candidate recoiling SMBHs. I will then describe our efforts to interpret these findings and make predictions for future observations using hydrodynamic simulations of galaxy mergers that include SMBHs. Because many candidate SMBH pairs have been identified as double-peaked narrow-line (NL) AGN, which may be associated with BH motion on kiloparsec scales, we have made a first attempt to model the NL region in galaxy merger simulations. In general, we find that double-peaked NL AGN are a short-lived but generic phase in gaseous major mergers, and that they arise from a varied combination of BH motion and gas kinematics. I will discuss the implications of our findings for follow-up confirmation of SMBH pair candidates. Additionally, I will summarize the results of our large study of recoiling SMBHs in galaxy merger simulations. I will describe the dynamics of recoil in gas-rich versus gas-poor mergers, as well as the possible effects of recoil on star formation and the BH-bulge relations. Recoiling SMBHs may be observed as kinematically- or spatially-offset AGN with lifetimes of up to tens of Myr; I will conclude by describing efforts to model a candidate recoiling SMBH that displays both types of offset.