PI: Xin Liu, U. of Illinois Urbana-Champaign, firstname.lastname@example.org
Address: Department of Astronomy, 103 Astronomy Building, 1002 West Green Street, Urbana, IL, 61801 USA
CoI: Yue Shen, U. of Illinois Urbana-Champaign
Title: Hunting for Massive Binary Black Holes with Continued Quasar Spectroscopic Monitoring
Abstract: We propose Gemini/GMOS-N spectroscopy for 13 candidate massive binary black holes (MBBHs; gravitationally bound with sub-pc separations) at redshifts 0.1<z<0.5. Systematically selected from the SDSS spectroscopic quasar catalog with two-epoch spectra, our targets show significant radial velocity shifts in the broad H-beta emission lines (corroborated by either H-alpha or Mg II) of a few hundred km/s over a few yrs (rest frame). Such radial velocity shifts may be the smoking gun signature for a MBBH where only one BH is active (similar to exoplanets), but only two epoch spectra cannot rule out alternative scenarios. To further test model assumptions, we propose third-epoch spectroscopy to continue monitoring the broad-line radial velocity shifts. While detecting a complete binary orbit would be challenging given that the orbital periods are expected to be a few decades at least, a continuing constant acceleration without changes in the line profile shape would already be a strong signature for a MBBH. The results will help constrain the frequency and evolution of sub-pc MBBHs, with implications for low-frequency gravitational wave sources and for the assembly and growth of massive black holes.
Program Type: Standard/Extragalactic
Run 1 (2016A): GEM-NQ/GMOSN -- 12hrs band 3 (GN-2016A-Q-83)
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