AGNs on the Move: A Search for Off-nuclear AGNs from Recoiling Supermassive Black Holes and Ongoing Galaxy Mergers with the Zwicky Transient Facility

Creators: Ward, Charlotte; Gezari, Suvi; Frederick, Sara; Hammerstein, Erica; Nugent, Peter; van Velzen, Sjoert; Drake, Andrew; García Pérez, Abigail; Oyoo, Immaculate; Bellm, Eric C.; Duev, Dmitry A.; Graham, Matthew J.; Kasliwal, Mansi M.; Kaye, Stephen; Mahabal, Ashish A.; Masci, Frank J.; Rusholme, Ben; Soumagnac, Maayane T.; Yan, Lin

Abstract

A supermassive black hole (SMBH) ejected from the potential well of its host galaxy via gravitational wave recoil carries important information about the mass ratio and spin alignment of the pre-merger SMBH binary. Such a recoiling SMBH may be detectable as an active galactic nucleus (AGN) broad-line region offset by up to 10 kpc from a disturbed host galaxy. We describe a novel methodology using forward modeling with The Tractor to search for such offset AGNs in a sample of 5493 optically variable AGNs detected with the Zwicky Transient Facility (ZTF). We present the discovery of nine AGNs that may be spatially offset from their host galaxies and are candidates for recoiling SMBHs. Five of these offset AGNs exhibit double-peaked broad Balmer lines, which may have arisen from unobscured accretion disk emission, and four show radio emission indicative of a relativistic jet. The fraction of double-peaked emitters in our spatially offset AGN sample is significantly larger than the 16% double-peaked emitter fraction observed for ZTF AGNs overall. In our sample of variable AGNs we also identified 52 merging galaxies, including a new spectroscopically confirmed dual AGN. Finally, we detected the dramatic rebrightening of SDSS 1133, a previously discovered variable object and recoiling SMBH candidate, in ZTF. The flare was accompanied by the reemergence of strong P Cygni line features, indicating that SDSS 1133 may be an outbursting luminous blue variable star.

Additional Information

© 2021. The American Astronomical Society. Received 2020 November 23; revised 2021 March 24; accepted 2021 March 24; published 2021 May 28. We thank the anonymous reviewer for their helpful feedback. S.G. is supported in part by National Science Foundation grant 1616566. This work relied on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the ZTF survey. ZTF is supported by the National Science Foundation under grant No. AST-1440341 and by a collaboration including Caltech, IPAC, the Weizmann Institute of Science, the Oskar Klein Centre at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratory, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratory. Operations are conducted by COO, IPAC, and UW. The SED Machine is based upon work supported by the National Science Foundation under grant No. 1106171. This work was supported by the GROWTH project funded by the National Science Foundation under grant No. 1545949. M.M.K. acknowledges generous support from the David and Lucile Packard Foundation. This research used resources of the National Energy Research Scientific Computing Center, a user facility supported by the Office of Science of the US Department of Energy (DOE) under contract No. DE-AC02-05CH11231. P.E.N. acknowledges support from the DOE under grant DE-AC02-05CH11231, Analytical Modeling for Extreme-scale Computing Environments. These results made use of the LDT at Lowell Observatory. Lowell is a private, nonprofit institution dedicated to astrophysical research and public appreciation of astronomy and operates the LDT in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University, and Yale University. The upgrade of the DeVeny optical spectrograph has been funded by a generous grant from John and Ginger Giovale. This project used data obtained with the DECam, which was constructed by the Dark Energy Survey (DES) collaboration. Funding for the DES projects has been provided by the DOE, the US National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, the Center for Cosmology and AstroParticle Physics at the Ohio State University, the Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundacao Carlos Chagas Filho de Amparo, Financiadora de Estudos e Projetos, Fundacao Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico and Ministerio da Ciencia, Tecnologia e Inovacao, Deutsche Forschungsgemeinschaft, and the collaborating institutions in the DES. The collaborating institutions are Argonne National Laboratory, the University of California at Santa Cruz, the University of Cambridge, Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas-Madrid, the University of Chicago, University College London, the DES-Brazil Consortium, the University of Edinburgh, Eidgenossische Technische Hochschule Zurich, Fermi National Accelerator Laboratory, the University of Illinois at Urbana-Champaign, Institut de Ciencies de l'Espai (IEEC/CSIC), Institut de Fisica d'Altes Energies, Lawrence Berkeley National Laboratory, Ludwig-Maximilians Universitat Munchen and the associated Excellence Cluster Universe, the University of Michigan, the National Optical Astronomy Observatory, the University of Nottingham, the Ohio State University, the University of Pennsylvania, the University of Portsmouth, SLAC National Accelerator Laboratory, Stanford University, the University of Sussex, and Texas A&M University. Software: Ampel (Nordin et al. 2019), Astropy (Robitaille et al. 2013; Price-Whelan et al. 2018), catsHTM (Soumagnac & Ofek 2018), extcats (github.com/MatteoGiomi/extcats), GROWTH Marshal (Kasliwal et al. 2019), The Tractor (Lang et al. 2016).

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