TY - JOUR

T1 - An improved test of the binary black hole hypothesis for quasars with double-peaked broad Balmer lines

AU - Doan, Anh

AU - Eracleous, Michael

AU - Runnoe, Jessie C.

AU - Liu, Jia

AU - Mathes, Gavin

AU - Flohic, Helene M.L.G.

N1 - Funding Information:
We thank Editage [www.editage.cn] for English language editing. This work was supported by the Shenzhen Science and Technology Innovation Committee [grant number JCYJ20180228163436705]; the China Postdoctoral Foundation [grant number 2018M633250]; and the National Natural Science Foundation of China (NSFC) [grant numbers 81400616, 31770876].
Funding Information:
This work was supported by the Shenzhen Science and Technology Innovation Committee [grant number JCYJ20180228163436705]; the China Postdoctoral Foundation [grant number 2018M633250]; and the National Natural Science Foundation of China (NSFC) [grant numbers 81400616, 31770876].
Publisher Copyright:
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society

PY - 2020/1/1

Y1 - 2020/1/1

N2 - Velocity offsets in the broad Balmer lines of quasars and their temporal variations serve as indirect evidence for bound supermassive black hole binaries (SBHBs) at sub-parsec separations. In this work, we test the SBHB hypothesis for 14 quasars with double-peaked broad emission lines using their long-term (14-41 yr) radial velocity curves. We improve on the previous work by (i) using elliptical instead of circular orbits for the SBHBs, (ii) adopting a statistical model for radial velocity jitter, (iii) employing a Markov chain Monte Carlo method to explore the orbital parameter space efficiently and build posterior distributions of physical parameters, and (iv) incorporating new observations. We determine empirically that jitter comprises approximately Gaussian distributed fluctuations about the smooth radial velocity curves that are larger than the measurement errors by factors of a few. We initially treat jitter by enlarging the effective error bars and then verify this approach via a variety of Gaussian process models for it. We find lower mass limits for the hypothesized SBHBs in the range 108-1011 M☉. For seven objects, the SBHB scenario appears unlikely based on goodness-of-fit tests. For two additional objects, the minimum SBHB masses are unreasonably large (>1010 M☉), strongly disfavouring the SBHB scenario. Using constraints on the orbital inclination angle (which requires some assumptions) makes the minimum masses of four more objects unreasonably large. We also cite physical and observational arguments against the SBHB hypothesis for nine objects. We conclude that the SBHB explanation is not the favoured explanation of double-peaked broad emission lines.

AB - Velocity offsets in the broad Balmer lines of quasars and their temporal variations serve as indirect evidence for bound supermassive black hole binaries (SBHBs) at sub-parsec separations. In this work, we test the SBHB hypothesis for 14 quasars with double-peaked broad emission lines using their long-term (14-41 yr) radial velocity curves. We improve on the previous work by (i) using elliptical instead of circular orbits for the SBHBs, (ii) adopting a statistical model for radial velocity jitter, (iii) employing a Markov chain Monte Carlo method to explore the orbital parameter space efficiently and build posterior distributions of physical parameters, and (iv) incorporating new observations. We determine empirically that jitter comprises approximately Gaussian distributed fluctuations about the smooth radial velocity curves that are larger than the measurement errors by factors of a few. We initially treat jitter by enlarging the effective error bars and then verify this approach via a variety of Gaussian process models for it. We find lower mass limits for the hypothesized SBHBs in the range 108-1011 M☉. For seven objects, the SBHB scenario appears unlikely based on goodness-of-fit tests. For two additional objects, the minimum SBHB masses are unreasonably large (>1010 M☉), strongly disfavouring the SBHB scenario. Using constraints on the orbital inclination angle (which requires some assumptions) makes the minimum masses of four more objects unreasonably large. We also cite physical and observational arguments against the SBHB hypothesis for nine objects. We conclude that the SBHB explanation is not the favoured explanation of double-peaked broad emission lines.

UR - http://www.scopus.com/inward/record.url?scp=85079696982&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85079696982&partnerID=8YFLogxK

U2 - 10.1093/mnras/stz2705

DO - 10.1093/mnras/stz2705

M3 - Article

AN - SCOPUS:85079696982

SN - 0035-8711

VL - 491

SP - 1104

EP - 1126

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

IS - 1

ER -