TY - JOUR
T1 - A large systematic search for close supermassive binary and rapidly recoiling black holes - III. Radial velocity variations
AU - Runnoe, Jessie C.
AU - Eracleous, Michael
AU - Pennell, Alison
AU - Mathes, Gavin
AU - Boroson, Todd
AU - Sigurðsson, Steinn
AU - Bogdanović, Tamara
AU - Halpern, Jules P.
AU - Liu, Jia
AU - Brown, Stephanie
N1 - Publisher Copyright:
© 2017 The Authors
PY - 2017/6/1
Y1 - 2017/6/1
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=85040446503&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85040446503&partnerID=8YFLogxK
U2 - 10.1093/mnras/stx452
DO - 10.1093/mnras/stx452
M3 - Article
AN - SCOPUS:85040446503
SN - 0035-8711
VL - 468
SP - 1683
EP - 1702
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 2
ER -