REBELS-IFU: Steeply rising star formation histories and the importance of dust obscuration in massive z ≃ 7 galaxies revealed by multiwavelength observations

Fisher, R ORCID: 0009-0008-3946-0502, Bowler, RAA ORCID: 0000-0003-3917-1678, Cochrane, RK ORCID: 0000-0001-8855-6107, Rowland, LE ORCID: 0009-0009-2671-4160, Stefanon, M, Algera, HSB ORCID: 0000-0002-4205-9567, Aravena, M, Bouwens, R, Da Cunha, E ORCID: 0000-0001-9759-4797, Dayal, P ORCID: 0000-0001-8460-1564, Ferrara, A, Hodge, JA, Inami, H ORCID: 0000-0003-4268-0393, Komarova, L, Smit, R ORCID: 0000-0001-8034-7802, Sommovigo, L ORCID: 0000-0002-2906-2200, Stark, DP and van der Werf, PP (2026) REBELS-IFU: Steeply rising star formation histories and the importance of dust obscuration in massive z ≃ 7 galaxies revealed by multiwavelength observations. Monthly Notices of the Royal Astronomical Society, 546 (3). ISSN 0035-8711

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Abstract

Reliable star formation rate (SFR) measurements are essential for understanding early galaxy evolution, yet derived values rely on several assumptions. To address this problem, we investigate the SFRs of 12 massive (9 < log(M<inf>⋆</inf>/M<inf>⊙</inf>) < 10) Lyman-break galaxies at z=6.5-7.7, drawn from the Atacama Large Millimeter/submillimeter Array (ALMA) Reionization Era Bright Emission Line Survey (REBELS) program. The multiwavelength data, including JWST NIRSpec IFU spectroscopy and ALMA observations, make this a unique sample for investigating SFR tracers at this epoch. We compare SFRs derived from the rest-UV, Hα, and far-infrared emission, and from spectral energy distribution (SED) fits. We apply robust dust attenuation corrections, which are crucial since between 50 and 80 per cent of the star formation is obscured, and find a stellar-to-nebular attenuation ratio of f=0.50 ± 0.08, consistent with local star-forming galaxies. The majority of the derived total SFRs (medians 25-120 M<inf>⊙</inf>yr^-1) place the REBELS galaxies systematically above z=7 literature star-forming main-sequence relations, and our best-fit star formation histories (SFHs) rise more steeply than lower-mass galaxies at the same redshift. We show that these rising SFHs mean commonly used luminosity-to-SFR conversion factors, derived assuming a constant SFH over given time-scales, overestimate the SFRs averaged over these time-scales for our galaxies. We provide updated luminosity-to-SFR calibrations for z ≃ 7 galaxies with rising SFHs, showing that commonly assumed rest-UV conversion factors overestimate the 100 Myr average SFR by a factor of ≃ 3. Finally, we investigate burstiness indicators in the REBELS-IFU galaxies, finding that the rising SFHs imply that the Hα-to-UV luminosity ratio is an unreliable probe of bursty star formation.

Item Type:	Article
Uncontrolled Keywords:	5101 Astronomical Sciences; 51 Physical Sciences; 7 Affordable and Clean Energy; 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:	29 December 2025
Date of first compliant Open Access:	12 June 2026
Date Deposited:	12 Jun 2026 10:17
Last Modified:	12 Jun 2026 10:17
DOI or ID number:	10.1093/mnras/stag049
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28820

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