JWST’s PEARLS: A z ≃ 6 quasar in a train-wreck galaxy merger system

¹ Los Alamos National Laboratory, Los Alamos, NM 87545, USA
² School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, USA
³ School of Physics, University of Melbourne, Parkville, VIC 3010, Australia
⁴ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
⁵ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁶ INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, Via A. Corti 12, I-20133 Milano, Italy
⁷ Department of Astronomy & Astrophysics, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
⁸ Dept. of Physics and Astronomy, University of Alabama, Box 870324 Tuscaloosa, AL 35404, USA
⁹ Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA
¹⁰ International Centre for Radio Astronomy Research (ICRAR) and the International Space Centre (ISC), The University of Western Australia, M468, 35 Stirling Highway, Crawley, WA 6009, Australia
¹¹ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹² Association of Universities for Research in Astronomy (AURA) for the European Space Agency (ESA), STScI, Baltimore, MD 21218, USA
¹³ Center for Astrophysical Sciences, Department of Physics and Astronomy, The Johns Hopkins University, 3400 N Charles St., Baltimore, MD 21218, USA
¹⁴ Jodrell Bank Centre for Astrophysics, Alan Turing Building, University of Manchester, Oxford Road, Manchester M13 9PL, UK
¹⁵ Instituto de Física de Cantabria (CSIC-UC), Avenida. Los Castros s/n., 39005 Santander, Spain
¹⁶ Department of Astronomy/Steward Observatory, University of Arizona, 933 N Cherry Ave, Tucson, AZ 85721-0009, USA
¹⁷ Steward Observatory, University of Arizona, 933 N Cherry Ave, Tucson, AZ 85721-0009, USA
¹⁸ Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA
¹⁹ Department of Astronomy, University of Maryland, College Park 20742, USA
²⁰ Physics Department, Ben-Gurion University of the Negev, P.O. Box 653 Be’er-Sheva 8410501, Israel
²¹ Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS, Beijing 100101, China
²² Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
²³ Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong
²⁴ Centro de Astrobiología (CAB), CSIC-INTA, Ctra. de Ajalvir km 4, Torrejón de Ardoz, E-28850 Madrid, Spain
²⁵ Max-Planck-Institut für extraterrestrische Physik, Gießenbachstraße 1, 85748 Garching, Germany
²⁶ National Research Council of Canada, Herzberg Astronomy & Astrophysics Research Centre, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
²⁷ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
²⁸ Cavendish Laboratory – Astrophysics Group, University of Cambridge, 19 JJ Thomson Avenue, Cambridge CB3 0HE, UK

^⋆ Corresponding author: mmarshall@lanl.gov

Received: 27 February 2025
Accepted: 15 August 2025

Abstract

We present JWST NIRSpec integral field spectroscopy observations of the z = 5.89 quasar NDWFS J1425+3254 from 0.6–5.3 μm, covering the rest-frame ultraviolet and optical at a spectral resolution of R ∼ 100. The quasar has a black hole mass of M_BH = (1.4^+3.1_−1.0) × 10⁹ M_⊙ and an Eddington ratio of L_Bol/L_Edd = 0.3^+0.6_−0.2, as implied from the broad Balmer Hα and Hβ lines. The quasar host has significant ongoing obscured star formation, as well as a quasar-driven outflow with velocity 6050⁺⁴⁶⁰₋₆₃₀ km s⁻¹ and ionised outflow rate of 1650⁺¹³⁰₋₁₂₃₀ M_⊙ yr⁻¹. This is possibly one of the most extreme outflows in the early Universe. The data also reveal that two companion galaxies are merging with the quasar host. The north-eastern companion galaxy is relatively old and very massive, with a luminosity-weighted stellar age of 65⁺⁹₋₄ Myr, stellar mass of (3.6^+0.6_−0.3 #x00D7; 10¹¹ M_⊙, and star-formation rate (SFR) of ∼15–30 M_⊙ yr⁻¹. A bridge of gas connects this companion galaxy and the host, confirming their ongoing interaction. A second merger is occurring between the quasar host and a much younger companion galaxy to the south, with a stellar age of 6.7 ± 1.8 Myr, stellar mass of (1.9 ± 0.4)×10¹⁰ M_⊙, and SFR of ∼40–65 M_⊙ yr⁻¹. There is also another galaxy in the field, likely in the foreground at z = 1.135, which could be gravitationally lensing the quasar with a magnification of 1 < μ < 2 and, thus, < 0.75 mag. Overall, the system is a ‘train-wreck’ merger of three galaxies, with star formation and extreme quasar activity that were likely triggered by these ongoing interactions.