SEARCHING for BINARY SUPERMASSIVE BLACK HOLES VIA VARIABLE BROAD EMISSION LINE SHIFTS: LOW BINARY FRACTION

Lile Wang, Jenny E. Greene, Wenhua Ju, Roman R. Rafikov, John J. Ruan, Donald P. Schneider

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

Supermassive black hole binaries (SMBHs) are expected to result from galaxy mergers, and thus are natural byproducts (and probes) of hierarchical structure formation in the universe. They are also the primary expected source of low-frequency gravitational wave emission. We search for binary BHs using time-variable velocity shifts in broad Mg ii emission lines of quasars with multi-epoch observations. First, we inspect velocity shifts of the binary SMBH candidates identified in Ju et al., using Sloan Digital Sky Survey spectra with an additional epoch of data that lengthens the typical baseline to ∼10 yr. We find variations in the line of sight velocity shifts over 10 yr that are comparable to the shifts observed over 1-2 yr, ruling out the binary model for the bulk of our candidates. We then analyze 1438 objects with eight-year median time baselines, from which we would expect to see velocity shifts >1000 km s-1 from sub-parsec binaries. We find only one object with an outlying velocity of 448 km s-1, indicating - based on our modeling - that ≲1% (the value varies with different assumptions) of SMBHs that are active as quasars reside in binaries with ∼0.1 pc separations Binaries either sweep rapidly through these small separations or stall at larger radii.

Original languageEnglish (US)
Article number129
JournalAstrophysical Journal
Volume834
Issue number2
DOIs
StatePublished - Jan 10 2017

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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