UGC 2369S: A Kiloparsec-scale Triple Merger Candidate Identified in a Nearby Luminous Infrared Galaxy
Year: 2026
Type: article
Abstract: We present high-spatial-resolution (≲1 . ″ 0), multiwavelength observations of UGC 2369S, a nearby luminous infrared galaxy showing three distinct cores separated on kiloparsec scales in near-infrared (NIR) imaging with significant X-ray emission. Utilizing optical/NIR adaptive optics, radio, Chandra X-ray, as well as archival Hubble Space Telescope imaging, we perform a comprehensive study of active galactic nuclei (AGN) activity, obscuration, and host properties. As one of the clearest cases of a triple-nucleus merger at ≃3 kpc separations, UGC 2369S is the first to be studied with high-resolution observations at multiple wavelengths. We find that the northern core, having possibly the most massive black hole (BH) in the system ( M BH ≃ 10 8 M ⊙ ), is consistent with a heavily obscured AGN. However, its high dust extinction ( A v > 5), hydrogen column density ( N H ≳ 10 25 cm −2 ), and nondetection of optical coronal lines and coronal X-ray emission leave the identification inconclusive. The other two cores show no evidence for black-hole activity and instead exhibit signatures of tidal disruption. From stellar mass surface density and stellar velocity dispersion maps, we infer that the strongly varying gravitational potential in this three-body system may have cannibalized the stellar bulge of the southwestern core, leaving a metal-enriched remnant. An ongoing survey focusing on similar triple systems could help us understand how they evolve and help benchmark numerical simulations, providing insight into gravitational wave predictions and the formation of the most massive BHs.
Source: The Astrophysical Journal
Institutions: California Institute of Technology, Eureka Scientific, University of California, Berkeley, Peking University, Max Planck Institute for Extraterrestrial Physics, Texas A&M University, Pontificia Universidad Católica de Chile, Yale University, University of Geneva, Universidad Diego Portales, Atacama Large Millimeter Submillimeter Array, European Southern Observatory, University of Tarapacá, Northwestern University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Awards: G2595738051, THE NUCLEI OF THE MOST ACTIVE GALAXIES IN THE LOCAL UNIVERSE AT THE HIGHEST RESOLUTIONS, AN UNPRECEDENTED CENSUS OF BLACK HOLE ACTIVITY IN THE LSST ERA, G4502643054, A COMPREHENSIVE VIEW OF THE CONNECTION BETWEEN SUPERMASSIVE BLACK HOLE GROWTH AND MAJOR GALAXY MERGERS, G57481727, THE SHARPEST VIEW OF SUPERMASSIVE BLACK HOLE GROWTH AND STAR FORMATION IN THE NUCLEAR REGION OF MAJOR GALAXY MERGERS, Programs on Critical Problems in Physics, Astrophysics and Biophysics at the Aspen Center for Physics, SPECTRO-TEMPORAL STUDIES OF AGN POPULATIONS, CENTRO DE ASTROFISICA Y TECNOLOGIAS AFINES (CATA)
OpenAlex ID: W7160209476