UGC 4211: A Confirmed Dual Active Galactic Nucleus in the Local Universe at 230 pc Nuclear Separation

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-SanchezKyuseok Oh, T. Taro Shimizu, Krista Lynne Smith, Daniel Stern, Miguel Parra Tello, C. Megan Urry

Research output: Contribution to journalArticlepeer-review

Abstract

We present multiwavelength 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/Space Telescope Imaging Spectrograph, Very Large Telescope/MUSE+AO, Keck/OSIRIS+AO spectroscopy, and the Atacama Large Millimeter/submillimeter Array (ALMA) observations, we show that the spatial distribution, optical and near-infrared 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, suggest that both SMBHs have similar masses, log M BH / M ⊙ ∼ 8.1 (south) and log M BH / M ⊙ ∼ 8.3 (north), respectively. The projected separation of 230 pc (∼6× the black hole sphere of influence) represents the closest-separation dual active galactic nuclei (AGN) studied to date with multiwavelength 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 subkiloparsec regime at the final stages of dynamical friction provide important constraints for future gravitational wave observatories.

Original languageEnglish
Article numberL24
JournalAstrophysical Journal Letters
Volume942
Issue number1
DOIs
StatePublished - 1 Jan 2023

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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