GA-NIFS: Black hole and host galaxy properties of two z-6.8 quasars from the NIRSpec IFU

Abstract

Aims. Integral field spectroscopy (IFS) with JWST NIRSpec will significantly improve our understanding of the first quasars, by providing spatially resolved, infrared spectroscopic capabilities that cover key rest-frame optical emission lines that have been previously unobservable. Methods. Here we present our results from the first two z>6 quasars observed as a part of the Galaxy Assembly with NIRSpec IFS (GA-NIFS) GTO programme, with DELS J0411-0907 at z=6.82 and VDES J0020-3653 at z=6.86. Results. By observing the Hβ, [O III] λλ4959,-5007, and Hα emission lines in these high-z quasars for the first time, we measured accurate black hole masses, MBH=1.85-0.8+2×109 M⊙ and 2.9-1.3+3.5×109M⊙, corresponding to Eddington ratios of λEdd=0.8-0.4+0.7 and 0.4-0.2+0.3 for DELS J0411-0907 and VDES J0020-3653, respectively. These provide a key comparison for existing estimates from the more uncertain Mg II line. We performed quasar-host decomposition using models of the quasars-broad lines to measure the underlying host galaxies. We also discovered multiple emission line regions surrounding each of the host galaxies, which are likely companion galaxies undergoing mergers with these hosts. We measured the star formation rates, excitation mechanisms, and dynamical masses of the hosts and companions, measuring the MBH/Mdyn ratios at high z using these estimators for the first time. DELS J0411-0907 and VDES J0020-3653 both lie above the local black hole-host mass relation, and are consistent with the existing observations of z≳6 quasar host galaxies with ALMA. We detected ionised outflows in [O ¯III] λλ4959,-5007 and Hβ from both quasars, with mass outflow rates of 58-37+44 and 525-92+75 M⊙ yr-1 for DELS J0411-0907 and VDES J0020-3653, much larger than their host star formation rates of < 33 and < 54 M⊙ yr-1, respectively. Conclusions. This work highlights the exceptional capabilities of the JWST NIRSpec IFU for observing quasars in the early Universe.