Seven wonders of Cosmic Dawn: JWST confirms a high abundance of galaxies and AGN at z ≃ 9–11 in the GLASS field

¹ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00078 Monteporzio Catone, Italy
² Dipartimento di Fisica, Università di Roma Sapienza, Città Universitaria di Roma – Sapienza, Piazzale Aldo Moro, 2, 00185 Roma, Italy
³ NSF’s National Optical-Infrared Astronomy Research Laboratory, 950 N. Cherry Ave., Tucson, AZ 85719, USA
⁴ Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, I-20133 Milano, Italy
⁵ Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Gobetti 93/3, I-40129 Bologna, Italy
⁶ INAF – Osservatorio astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
⁷ Dipartimento di Fisica e Astronomia ‘Galileo Galilei’, Università degli studi di Padova, Vicolo dell’Osservatorio, 3, I-35122 Padova, Italy
⁸ Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica, 1, 00133 Roma, Italy
⁹ IPAC, California Institute of Technology, MC 314-6, 1200 E. California Boulevard, Pasadena, CA 91125, USA
¹⁰ National Astronomical Research Institute of Thailand (NARIT), Mae Rim, Chiang Mai 50180, Thailand
¹¹ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290 Versoix, Switzerland
¹² Department of Physics and Astronomy, University of California, Los Angeles, 430 Portola Plaza, Los Angeles, CA 90095, USA
¹³ Dipartimento di Fisica e Scienze della Terra, Universit‘a degli Studi di Ferrara, Via Saragat 1, I-44122 Ferrara, Italy
¹⁴ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
¹⁵ National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo, Japan
¹⁶ School of Astronomy and Space Science, University of Chinese Academy of Sciences (UCAS), Beijing 100049, China
¹⁷ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China
¹⁸ Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University, Beijing 102206, China
¹⁹ Department of Space, Earth, & Environment, Chalmers University of Technology, Chalmersplatsen 4, 412 96 Gothenburg, Sweden

^⋆ Corresponding author; lorenzo.napolitano@inaf.it

Received: 2 September 2024
Accepted: 18 November 2024

Abstract

We present the JWST/NIRSpec PRISM follow-up of candidate galaxies at z ≃ 9–11 selected from deep JWST/NIRCam photometry in GLASS-JWST Early Release Science data. We spectroscopically confirm six sources with secure redshifts at z = 9.52–10.43, each showing multiple emission lines. An additional object is likely at z ≃ 10.66, based on its Lyα-break and a single emission feature, while one source is a lower-redshift interloper. The sample includes the first JWST-detected candidate at z ∼ 10, GHZ1/GLASS-z10, which we confirm at z = 9.875, and the X-ray detected active galactic nucleus (AGN) GHZ9 at z = 10.145. Three objects, including GHZ9, have EW(C III]λ1908) > 20 Å and occupy a region compatible with AGN emission in the EW(CIII]) vs CIV/CIII] diagram. The spectroscopic sample confirms a high abundance of galaxies at z > 9. We measure a number density of z ∼ 10 galaxies in the GLASS-JWST ERS field that is a factor of > 3 higher than other JWST-based estimates at demagnified rest-frame magnitudes of −21 ≤ M_UV ≤ −19. We find that the positions of these galaxies in redshift and angular space are not consistent with all of them being part of a single progenitor of present-day galaxy clusters. The high density of objects in the GLASS region can be explained either by clustering on large scales or by a superposition of different forming structures of which we observe only the brightest members. By considering all the spectroscopic z ∼ 10 sources in the Abell-2744 field, we identify two potential galaxy proto-clusters centered around GHZ9 and JD1, with relative separations between their members of ≃1–2 pMpc. The potential AGN nature of three of the sources in our sample lends support to a scenario in which the high abundance of bright sources determined by JWST surveys at cosmic dawn may be affected by AGN contribution to their UV luminosity.