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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

Abstract:

We report the discovery of a remarkable Lyα emitting galaxy at z = 7.2782, JADES-GS+53.16746-27.7720 (shortened to JADES-GS-z7-LA), with rest-frame equivalent width, EW0(Lyα) = 388.0 ± 88.8 Å and UV magnitude -17.0. The spectroscopic redshift is confirmed via rest-frame optical lines [O- ¯II], Hβ and [O- ¯III] in its JWST/NIRSpec Micro-Shutter Assembly (MSA) spectrum. The Lyα line is detected in both lower resolution (R ∼ 100) PRISM as well as medium resolution (R ∼ 1000) G140M grating spectra. The line spread function-deconvolved Lyα full width at half maximum in the grating is 383.9 ± 56.2 km s-1 and the Lyα velocity offset compared to the systemic redshift is 113.3 ± 80.0 km s-1, indicative of very little neutral gas or dust within the galaxy. We estimate the Lyα escape fraction to be > 70%. JADES-GS-z7-LA has a [O- ¯III]/[O- ¯II] ratio (O32) of 11.1 ± 2.2 and a ([O- ¯III] + [O- ¯II])/Hβ ratio (R23) of 11.2 ± 2.6, consistent with low metallicity and high ionization parameters. Deep NIRCam imaging also revealed a close companion source (separated by 0.23- ³), which exhibits similar photometry to that of JADES-GS-z7-LA, with a photometric excess in the F410M NIRCam image consistent with [O- ¯III] + Hβ emission at the same redshift. The spectral energy distribution of JADES-GS-z7-LA indicates a bursty star formation history, with a low stellar mass of 107† M·. Assuming that the Lyα transmission through the intergalactic medium is the same as its measured escape fraction, an ionized region of size > 1.5 pMpc is needed to explain the high Lyα EW and low velocity offset compared to systemic seen in JADES-GS-z7-LA. Owing to its UV-faintness, we show that it is incapable of single-handedly ionizing a region large enough to explain its Lyα emission. Therefore, we suggest that JADES-GS-z7-LA (and possibly the companion source) may be a part of a larger overdensity, presenting direct evidence of overlapping ionized bubbles at z > 7