James Webb Space Telescope Feed Post

Harvard ADS: GA-NIFS & EIGER: A merging quasar host at z=7 with an overmassive black hole

Paper abstract: 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^{10}M_\odot, suggesting that this is a major galaxy interaction. Through detailed quasar subtraction and SED fitting using the NIRCam data, we obtain an estimate of the host stellar mass of M_{\ast}~eq2.6\times10^9M_\odot, with M_{*}~eq5.0\times10^9M_\odot for the companion galaxy. Using the H\beta Balmer line we estimate a virial black hole mass of M_{\rm{BH}}~eq1.4\times10^9 M_\odot. Thus, J1120+0641 has an extreme black hole - stellar mass ratio of M_{\rm{BH}}/M_\ast~eq0.54, 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.