A Candidate Dual Active Galactic Nucleus at z = 1.175
The X-ray source CXOXBJ142607.6+353351 (CXOJ1426+35), which was identified in a 172 ks Chandra image in the Boötes field, shows double-peaked rest-frame optical/UV emission lines, separated by 0"69 (5.5 kpc) in the spatial dimension and by 690 km s^(–1) in the velocity dimension. The high excitation lines and emission line ratios indicate both systems are ionized by an active galactic nucleus (AGN) continuum, and the double-peaked profile resembles that of candidate dual AGNs. At a redshift of z = 1.175, this source is the highest redshift candidate dual AGN yet identified. However, many sources have similar emission line profiles for which other interpretations are favored. We have analyzed the substantial archival data available in this field as well as acquired near-infrared (NIR) adaptive optics (AO) imaging and NIR slit spectroscopy. The X-ray spectrum is hard, implying a column density of several 10^(23) cm^(–2). Though heavily obscured, the source is also one of the brightest in the field, with an absorption-corrected 2-10 keV luminosity of ~10^(45) erg s^(–1). Outflows driven by an accretion disk may produce the double-peaked lines if the central engine accretes near the Eddington limit. However, we may be seeing the narrow line regions of two AGNs following a galactic merger. While the AO image reveals only a single source, a second AGN would easily be obscured by the significant extinction inferred from the X-ray data. Understanding the physical processes producing the complex emission line profiles seen in CXOJ1426+35 and related sources is important for interpreting the growing population of dual AGN candidates.
Additional Information© 2012 The American Astronomical Society. Received 2011 April 4; accepted 2011 September 13; published 2011 December 7. The authors thank an anonymous referee for helpful comments that greatly improved the quality of the paper. The authors gratefully acknowledge discussions on similar dual AGN candidates with close collaborators, especially Claud Lacy, Daniel Kennefick, Julia Kennefick, and Joel Berrier. R.S.B. is also grateful to D.S. for funding an extended visit to JPL in Summer 2010. A.H.G. acknowledges support from the National Science Foundation under grant AST-0708490. This research was partially carried out at the Jet Propulsion Laboratory/California Institute of Technology and was sponsored by the Strategic University Research Partnership Program and the National Aeronautics and Space Administration. This work is based in part on observations obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. This work is based in part on observations obtained with Chandra, under contract SV4-74018, A31 with the Smithsonian Astrophysical Observatory which operates the CXO for NASA. This work makes use of image data from the NOAO DeepWide-Field Survey (NDWFS) as distributed by the NOAO Science Archive. NOAO is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation. This paper would not have been possible without the efforts of the Spitzer, Chandra, and Keck support staff.
Published - Barrows2012p16870Astrophys_J.pdf