Discovery of a Population of Close Binary AGN: Observing the Hierarchical Assembly of Supermassive Black Holes
Abstract
Hierarchial structure formation predicts that as galaxies merge, so will their ubiquitous central supermassive black holes (SMBH), and thus binary SMBHs should be fairly common. Yet until recently, very few such cases were known, mostly as serendipitous, heterogeneous detections. We initiated a survey for close binary AGN, using diffraction-limited LGS AO imaging with the Keck telescope. The target sample is selected from a sample of SDSS AGN whose spectra display double narrow [O III] emission lines, possibly indicative of close binary AGN. A subset of the apparent double systems is then followed up by LGS AO IFU spectroscopy, in order to establish their physical nature. In an initial sample of 50 targets, we discovered 16 apparent close binary AGN. A subset of these has been followed by IFU spectroscopy, which indicates that the gas is indeed ionized by AGN. Thus, we have established the existence of a population of close binary SMBH in the ongoing merger systems. We find that the fraction of apparent SMBH binaries increases with redshift, in a way which is consistent with the observed galaxy merger fraction, as expected from the hierarchical assembly picture. We also find that the resolved binary SMBH systems represent outliers in the observed MBH - σ relation. Thus, pre-merger SMBH binaries can account for at least some of the observed scatter of this relation, which is used as one of the empirical constraints for the models of AGN feedback and co-evolution of galaxies and their SMBHs.
- Publication:
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American Astronomical Society Meeting Abstracts #217
- Pub Date:
- January 2011
- Bibcode:
- 2011AAS...21731007D