Galaxy formation and evolution

Abstract:

Recent discoveries of faint active galactic nuclei (AGN) at the redshift frontier have revealed a plethora of broad Hα emitters with optically red continua, named little red dots (LRDs)1, which comprise 15–30% of the high-redshift broad-line AGN population2. Owing to their peculiar properties3, 4, 5–6, modelling LRDs with standard AGN scenarios has proven challenging. In particular, the validity of single-epoch virial mass estimates in determining the black-hole masses of LRDs has been called into question, with some models claiming that masses might be overestimated by up to two orders of magnitude7, 8, 9–10. Here we report a direct, dynamical black-hole mass measurement in a strongly lensed LRD at a redshift of 7.04. The combination of lensing with deep spectroscopic data reveals a rotation curve that is inconsistent with a nuclear star cluster, yet can be well explained by Keplerian rotation around a point mass of 50 million solar masses, consistent with virial black-hole mass estimates. The Keplerian rotation leaves little room for any stellar component in a host galaxy, as we conservatively infer MBH/M⁎ > 2 (where MBH is the black-hole mass and M⁎ is the stellar mass). Such a ‘naked’ black hole, together with its near-pristine environment11, indicates that this LRD is a massive black-hole seed caught in its earliest accretion phase.

Abstract:

This paper accompanies Data Release 4 of the James Webb Space Telescope (JWST) Advanced Deep Extragalactic Survey, which presents the full NIRSpec spectroscopy of the survey. We provide spectra of 5190 targets across Great Observatories Origins Deep Survey (GOODS)-North and GOODS-South (including the Hubble Ultra Deep Field), observed with the low-dispersion (–300) prism and three medium-resolution () gratings spanning m; 2654 were also observed with the higher resolution () G395H grating. The tiered survey design obtained h exposures for galaxies in the Deep and Ultra Deep tiers, and shallower observations (–3 h per setting) of galaxies in the Medium tiers. Targets were selected from photometric redshifts or colours, with priority given to rest-UV-selected galaxies at and F444W-selected galaxies at . We describe the full target selection and present spectroscopic redshifts and success rates. In total, we obtain robust redshifts for 3297 galaxies, including 396 at and 2545 at . To facilitate uniform analyses, we define ‘gold’ subsamples based on UV- and F444W-selection. Using the parent samples and redshift success rates, we construct rest-UV luminosity functions at from the Medium- and Deep-JWST tiers. Our number densities agree well with previous determinations from both photometric and spectroscopic samples, with modest interloper fractions confirming the reliability of photometric UV-bright galaxy selections at these redshifts.