REBELS-IFU: evidence for metal-rich massive galaxies at z ∼ 6−8

Rowland, LE ORCID: 0009-0009-2671-4160, Stefanon, M, Bouwens, R, Hodge, J, Algera, H ORCID: 0000-0002-4205-9567, Fisher, R ORCID: 0009-0008-3946-0502, Dayal, P ORCID: 0000-0001-8460-1564, Pallottini, A ORCID: 0000-0002-7129-5761, Stark, DP, Heintz, KE ORCID: 0000-0002-9389-7413, Aravena, M, Bowler, RAA ORCID: 0000-0003-3917-1678, Cescon, K, Endsley, R ORCID: 0000-0003-4564-2771, Ferrara, A, Fudamoto, Y, Gonzalez, V, Graziani, L, Gulis, C, Herard-Demanche, T ORCID: 0000-0003-2164-7949 et al (2026) REBELS-IFU: evidence for metal-rich massive galaxies at z ∼ 6−8. Monthly Notices of the Royal Astronomical Society, 546 (2). ISSN 0035-8711

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Abstract

Metallicity is a crucial tracer of galaxy evolution, providing insights into gas accretion, star formation, and feedback. At high redshift, these processes reveal how early galaxies assembled and enriched their interstellar medium. In this work, we present rest-frame optical spectroscopy of 12 massive (log(M/M) > 9) galaxies at z~ 6-8 from the Reionization Era Bright Emission Line Survey (REBELS) Atacama Large Millimetre/submillimetre Array (ALMA) large program, observed with the James Webb Space Telescope (JWST) NIRSpec integral field unit spectroscopy in the prism mode. These observations span emission lines from [Ο π]λλ3727,9 το [5 π]λλ6716,31, providing key information on nebular dust attenuation, ionization states, and chemical abundances. We find lower 032 ratios (average~3.7) and [OⅢ]25007 equivalent widths (median EW[om]~480 Å) than are generally found in existing large spectroscopic surveys at z > 6 indicating less extreme ionizing conditions. Strong-line diagnostics suggest that these systems are some of the most metal-rich galaxies observed at z > 6 (average Zyas~0.42)。 including sources with near-solar oxygen abundances, in line with their high stellar masses (average log M./M~9.5). Supplementing with literature sources at lower masses, we investigate the mass-metallicity and fundamental metallicity relations (MZR and FMR, respectively) over a 4 dex stellar mass range at 6 < z < 8 In contrast to recent studies of lower mass galaxies, we find no evidence for negative offsets to the z = 0 FMR for the REBELS galaxies. This work demonstrates the existence of chemically enriched galaxies just 1 Gyr after the big bang, and indicates that the MZR is already in place at these early times, in agreement with other recent z > 3 studies.

Item Type:	Article
Uncontrolled Keywords:	galaxies: evolution; galaxies: high-redshift - galaxies: ISM; 5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press
Date of acceptance:	21 October 2025
Date of first compliant Open Access:	11 June 2026
Date Deposited:	11 Jun 2026 13:11
Last Modified:	11 Jun 2026 13:11
DOI or ID number:	10.1093/mnras/staf2023
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28815

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