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Modeling the Observability of Recoiling Black Holes as Offset Quasars

Published online by Cambridge University Press:  27 October 2016

Laura Blecha
Affiliation:
University of Maryland, Dept. of Astronomy, College Park, MD, USA
Paul Torrey
Affiliation:
Massachusetts Institute of Technology, Cambridge, MA, USA
Mark Vogelsberger
Affiliation:
Massachusetts Institute of Technology, Cambridge, MA, USA
Shy Genel
Affiliation:
Columbia University, New York, NY, USA
Volker Springel
Affiliation:
Heidelberg Institute for Theoretical Studies, Heidelberg, Germany
Debora Sijacki
Affiliation:
Institute of Astronomy, Cambridge University, Madingley Road, Cambridge, UK
Gregory Snyder
Affiliation:
Space Telescope Science Institute, Baltimore, MD, USA
Simeon Bird
Affiliation:
Carnegie Mellon University, Pittsburgh, PA, USA
Dylan Nelson
Affiliation:
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
Dandan Xu
Affiliation:
Heidelberg Institute for Theoretical Studies, Heidelberg, Germany
Lars Hernquist
Affiliation:
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
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Abstract

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The merger of two supermassive black holes (SMBHs) imparts a gravitational-wave (GW) recoil kick to the remnant SMBH, which can even eject the SMBH from its host galaxy. An actively-accreting, recoiling SMBH may be observable as an offset quasar. Prior to the advent of a space-based GW observatory, detections of these offset quasars may offer the best chance for identifying recent SMBH mergers. Indeed, observational searches for recoiling quasars have already identified several promising candidates. However, systematic searches for recoils are currently hampered by large uncertainties regarding how often offset quasars should be observable and where they are most likely to be found. Motivated by this, we have developed a model for recoiling quasars in a cosmological framework, utilizing information about the progenitor galaxies from the Illustris cosmological hydrodynamic simulations. For the first time, we model the effects of BH spin alignment and recoil dynamics based on the gas-richness of host galaxies. We predict that if BH spins are not highly aligned, seeing-limited observations could resolve offset AGN, making them promising targets for all-sky surveys. The rarity of large broad-line offsets among SDSS quasars is likely due in part to selection effects but suggests that spin alignment plays a role in suppressing recoils. Nonetheless, in our most physically motivated model where alignment occurs only in gas-rich mergers, hundreds of offset AGN should be found in all-sky surveys. Our findings strongly motivate a dedicated search for recoiling AGN.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2016 

References

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