Browsing by Author "Blecha, Laura"

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    A population of luminous accreting black holes with hidden mergers
    (2018) Koss, Michael J.; Blecha, Laura; Bernhard, Phillip; Hung, Chao-Ling; Lu, Jessica R.; Trakhtenbrot, Benny; Treister, Ezequiel; Weigel, Anna; Sartori, Lia F.; Mushotzky, Richard; Schawinski, Kevin; Ricci, Claudio; Veilleux, Sylvain; Sanders, David B.
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    Molecular Gas in Major Mergers Hosting Dual and Single AGNs at
    (2025) Johnstone, Makoto A.; Treister, Ezequiel; Bauer, Franz E.; Chin-Shin Chang; Cicone, Claudia; Koss, Michael J.; Del Moral Castro, Ignacio; Muller Sanchez, Francisco; Privon, George C.; Ricci, Claudio; Scoville, Nick; Venturi, Giacomo; Barcos Muñoz, Loreto; Armus, Lee; Blecha, Laura; Casey, Caitlin; Comerford, Julia; Evans, Aaron; Kawamuro, Taiki; Medling, Anne M.; Messias, Hugo; Nagar, Neil; Rojas, Alejandra; Sanders, David; Trakhtenbrot, Benny; U, Vivian; Urry, Meg
    We present high-resolution (∼50–100 pc) Atacama Large Millimeter/submillimeter Array observations of 12CO(2–1) or 12CO(1–0) emission in seven local (z ≲ 0.05) major mergers—five of which are dual active galactic nucleus (AGN) systems, and two of which are single AGN systems. We model the molecular gas kinematics through rotating disk profiles using a Bayesian Markov Chain Monte Carlo approach. The residuals were then used to isolate nonrotating components of the molecular gas—the most likely contributor to future supermassive black hole (SMBH) growth. We find that more-massive SMBHs have higher surface densities of nonrotating molecular gas within their sphere of influence. This potential molecular gas supply, however, does not correlate with the current accretion efficiency of the SMBHs, suggesting that only a fraction of the observed nonrotating gas is currently reaching the SMBH. Finally, we tentatively find no significant differences in the nuclear molecular gas masses of single-AGN and dual-AGN hosts, both within the SMBH sphere of influence and within the central kiloparsec. Our results indicate that the probability of occurrence of the dual AGN phenomenon is likely dependent on AGN variability and/or obscuration rather than the availability of molecular gas in the nuclear regions.
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    UGC 4211: A Confirmed Dual Active Galactic Nucleus in the Local Universe at 230 pc Nuclear Separation
    (2023) Koss, Michael J.; Treister, Ezequiel; Kakkad, Darshan; Casey-Clyde, J. Andrew; Kawamuro, Taiki; Williams, Jonathan; Foord, Adi; Trakhtenbrot, Benny; Bauer, Franz E.; Privon, George C.; Ricci, Claudio; Mushotzky, Richard; Barcos-Munoz, Loreto; Blecha, Laura; Connor, Thomas; Harrison, Fiona; Liu, Tingting; Magno, Macon; Mingarelli, Chiara M. F.; Muller-Sanchez, Francisco; Oh, Kyuseok; Shimizu, T. Taro; Smith, Krista Lynne; Stern, Daniel; Tello, Miguel Parra; Urry, C. Megan
    We present multiwavelength high-spatial resolution (similar to 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, similar to 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-?) similar to 8.1 (south) and log (M-BH M-?) similar to 8.3 (north), respectively. The projected separation of 230 pc (similar to 6x 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.