Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Michael J. Koss
Ezequiel Treister
Darshan Kakkad
J. Andrew Casey-Clyde
Taiki Kawamuro
Jonathan Williams
Adi Foord
Benny Trakhtenbrot
Franz E. Bauer
George C. Privon
Claudio Ricci
Richard Mushotzky
Loreto Barcos-Munoz
Laura Blecha
Thomas Connor
Fiona Harrison
Tingting Liu
Macon Magno
Chiara M. F. Mingarelli
Francisco Muller-Sanchez
Abstract： We present multi-wavelength high-spatial resolution (~0.1'', 70 pc) observations of UGC 4211 at z=0.03474, a late-stage major galaxy merger at the closest nuclear separation yet found in near-IR imaging (0.32'', ~230 pc projected separation). Using Hubble Space Telescope/STIS, VLT/MUSE+AO, Keck/OSIRIS+AO spectroscopy, and ALMA observations, we show that the spatial distribution, optical and NIR emission lines, and millimeter continuum emission are all consistent with both nuclei being powered by accreting supermassive black holes (SMBHs). Our data, combined with common black hole mass prescriptions, suggests that both SMBHs have similar masses, log MBH~8.1 (south) and log MBH~8.3 (north), respectively. The projected separation of 230 pc (~6X the black hole sphere of influence) represents the closest-separation dual AGN studied to date with multi-wavelength resolved spectroscopy and shows the potential of nuclear (<50 pc) continuum observations with ALMA to discover hidden growing SMBH pairs. While the exact occurrence rate of close-separation dual AGN is not yet known, it may be surprisingly high, given that UGC 4211 was found within a small, volume-limited sample of nearby hard X-ray detected AGN. Observations of dual SMBH binaries in the sub-kpc regime at the final stages of dynamical friction provide important constraints for future gravitational wave observatories.
Peer Review Status:
Awaiting Review
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