GA-NIFS and EIGER: A merging quasar host at <em>z</em> = 7 with an overmassive black hole
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- doe_osti · checked 2025-10-06
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The James Webb Space Telescope is revolutionising our ability to understand the host galaxies and local environments of high-z quasars. Here we obtain a comprehensive understanding of the host galaxy of the z = 7.08 quasar J1120+0641 by combining NIRSpec integral field spectroscopy with NIRCam photometry of the host continuum emission. Our emission-line maps reveal that this quasar host is undergoing a merger with a bright companion galaxy. The quasar host and the companion have similar dynamical masses of ∼10<sup>10</sup> M<sub>⊙</sub>, suggesting that this is a major galaxy interaction. Through detailed quasar subtraction and SED fitting using the NIRCam data, we obtained an estimate of the host stellar mass of M<sub>∗</sub> = (3.0<sub>−1.4</sub><sup>+2.5</sup>) × 10<sup>9</sup> M<sub>⊙</sub>, with M<sub>∗</sub> = (2.7<sub>−0.5</sub><sup>+0.5</sup>) × 10<sup>9</sup> M<sub>⊙</sub> for the companion galaxy. Using the Hβ Balmer line, we estimated a virial black hole mass of M<sub>BH</sub> = (1.9<sub>−1.1</sub><sup>+2.9</sup>) × 109 M<sub>⊙</sub>. Thus, J1120+0641 has an extreme black hole–stellar mass ratio of M<sub>BH</sub>/M<sub>∗</sub> = 0.63<sub>−0.31</sub><sup>+0.54</sup>, which is ∼3 dex larger than expected by the local scaling relations between black hole and stellar mass. J1120+0641 is powered by an overmassive black hole with the highest reported black hole–stellar mass ratio in a quasar host that is currently undergoing a major merger. These new insights highlight the power of JWST for measuring and understanding these extreme first quasars.. Authors: Marshall, Madeline Anne [Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)] (ORCID:0000000164347845); Yue, Minghao [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)]; Eilers, Anna-Christina [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)]; Scholtz, Jan [Univ. of Cambridge (United Kingdom)]; Perna, Michele [Centro de Astrobiología (CSIC-INTA), Madrid (Spain)] (ORCID:0000000203625941). DOE Contract: 89233218CNA000001. Subjects: 79 ASTRONOMY AND ASTROPHYSICS; galaxies: high-redshift; galaxies: interactions; quasars: general; quasars: supermassive black holes