UNCOVER: A NIRSpec Census of Lensed Galaxies at z=8.50-13.08 Probing a High AGN Fraction and Ionized Bubbles in the Shadow

Abstract

We present JWST NIRSpec prism spectroscopy of gravitationally lensed galaxies at $z\gtrsim 9$ found behind the massive galaxy cluster Abell 2744 in the UNCOVER Cycle 1 Treasury Program. We confirm the source redshift via emission lines and/or the Ly$\alpha$ break feature for ten galaxies at z=8.50-13.08 down to $M_{\mathrm{UV}}=-17.3$. We achieve a high confirmation rate of 100\% for $z>9$ candidates reported in Atek et al. (2023). Using six sources with multiple emission line detections, we find that the offset of the redshift estimates between the lines and the Ly$\alpha$ break alone with prism can be as large as $\pm 0.2$, raising caution in designing future follow-up spectroscopy for the break-only sources with ALMA. With spec-$z$ confirmed sources in UNCOVER and the literature, we derive lower limits on the rest-frame ultraviolet (UV) luminosity function (LF) at $z\simeq 9$-12 and find these lower limits to be consistent with recent photometric measurements. We identify at least two unambiguous and several possible active galactic nucleus (AGN) systems based on X-ray emission, broad line (BL) H$\beta$, high ionization line (e.g., NIV]1487, CIV1549) detections, and excess in UVLF. This requires the AGN LFs at $z\simeq$ 9-10 to be comparable or even higher than the X-ray AGN LF estimated at $z\sim 6$ and indicates a plausible cause of the high abundance of $z>9$ galaxies claimed in recent photometric studies may be AGNs. One UV-luminous source is confirmed at the same redshift as a dusty BL AGN at $z=8.50$ with a physical separation of 380 kpc in the source plane. These two sources show blueward Ly$\alpha$ line or continuum emission, suggesting that they reside in the same ionized bubble with a radius of $7.69\pm 0.18$ pMpc. Our results imply that AGNs have a non-negligible contribution to cosmic reionization.

27 pages, 11 figures, 4 tables, ApJ in press

Cited by in corpus (9)

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• JWST UNCOVER: The Overabundance of Ultraviolet-luminous Galaxies at $z>9$
• The THESAN project: connecting ionized bubble sizes to their local environments during the Epoch of Reionization
• The first GLIMPSE of the faint galaxy population at Cosmic Dawn with JWST: The evolution of the ultraviolet luminosity function across z~9-15
• The impact of faint AGN discovered by JWST on reionization
• Optical and near-infrared spectroscopy of quasars at $z>6.5$: public data release and composite spectrum
• Probing AGN with spectropolarimetry: accretion disk and SMBH parameters
• The effect of helium reionization on the Lyman-alpha forest hydrogen flux statistics
• Ciii]$\lambda 1909$ emission as an alternative to Ly$\alpha$ in the reionization era: the dependence of Ciii] and Ly$\alpha$ at $3<z<4$ from the VANDELS survey