A large systematic search for close supermassive binary and rapidly recoiling black holes - III. Radial velocity variations

Jessie C. Runnoe, Michael Eracleous, Alison Pennell, Gavin Mathes, Todd Boroson, Steinn Sigurðsson, Tamara Bogdanović, Jules P. Halpern, Jia Liu, Stephanie Brown

Research output: Contribution to journalArticlepeer-review

33 Scopus citations

Abstract

We have been spectroscopically monitoring 88 quasars selected to have broad Hβ emission lines offset from their systemic redshift by thousands of km s−1. By analogy with single-lined spectroscopic binary stars, we consider these quasars to be candidates for hosting supermassive black hole binaries (SBHBs). In this work, we present new radial velocity measurements, typically three to four per object over a time period of up to 12 yr in the observer's frame. In 29/88 of the SBHB candidates, no variability of the shape of the broad Hβ profile is observed, which allows us to make reliable measurements of radial velocity changes. Among these, we identify three objects that have displayed systematic and monotonic velocity changes by several hundred km s−1 and are prime targets for further monitoring. Because the periods of the hypothetical binaries are expected to be long, we cannot hope to observe many orbital cycles during our lifetimes. Instead, we seek to evaluate the credentials of the SBHB candidates by attempting to rule out the SBHB hypothesis. In this spirit, we present a method for placing a lower limit on the period, and thus the mass, of the SBHBs under the assumption that the velocity changes we observe are due to orbital motion. Given the duration of our monitoring campaign and the uncertainties in the radial velocities, we were able to place a lower limit on the total mass in the range 4.7 × 104-3.8 × 108 M☉, which does not yet allow us to rule out the SBHB hypothesis for any candidates.

Original languageEnglish (US)
Pages (from-to)1683-1702
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Volume468
Issue number2
DOIs
StatePublished - Jun 1 2017

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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