EPOCHS. III. Unbiased UV Continuum Slopes at 6.5<z<13 from Combined PEARLS GTO and Public JWST/NIRCam Imaging

Austin, D, Conselice, CJ, Adams, NJ, Harvey, T, Duan, Q, Trussler, J, Li, Q, Juodžbalis, I, Ormerod, K ORCID: 0000-0003-2000-3420, Ferreira, L, Westcott, L, Harris, H, Wilkins, SM, Bhatawdekar, R, Caruana, J, Coe, D, Cohen, SH, Driver, SP, D’Silva, JCJ, Frye, B et al (2025) EPOCHS. III. Unbiased UV Continuum Slopes at 6.5<z<13 from Combined PEARLS GTO and Public JWST/NIRCam Imaging. The Astrophysical Journal, 995 (1). ISSN 0004-637X

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Abstract

We present an analysis of rest-frame UV continuum slopes, β, using a sample of 1011 galaxies at 6.5 < z < 13 from the EPOCHS photometric sample collated from the GTO PEARLS and public ERS/GTO/GO (JADES, CEERS, NGDEEP, GLASS) JWST/NIRCam imaging across 178.9 arcmin2 of unmasked blank sky. We correct our UV slopes for the photometric error coupling bias using 200,000 power-law spectral energy distributions for each β = {−1, −1.5, −2, −2.5, −3} in each field, finding biases as large as Δβ ≃ −0.55 for the lowest signal-to-noise ratio galaxies in our sample. Additionally, we simulate the impact of rest-UV line emission (including Lyα) and damped Lyα systems on our measured β, finding biases as large as 0.5–0.6 for the most extreme systems. We find a decreasing trend with redshift of β = −1.51 ± 0.08 − (0.097 ± 0.010) × z, with potential evidence for Population III stars or top-heavy initial mass functions in a subsample of 68 β + σβ < −2.8 galaxies. At z ≃ 11.5, we measure an extremely blue β(MUV = −19) = −2.73 ± 0.06, deviating from simulations, indicative of low-metallicity galaxies with nonzero Lyman continuum escape fractions fesc, LyC ≳ 0 and minimal dust content. The observed steepening of db/dlog10(M/M) from 0.22 ± 0.02 at z ≃ 7 to 0.81 ± 0.13 at z ≃ 11.5 implies that dust produced in core-collapse supernovae at early times may be ejected via outflows from low-mass galaxies. We also observe a flatter dβ/dMUV = 0.03 ± 0.02 at z ≃ 7 and a shallower db/dlog10(M/M) at z < 11 than seen by the Hubble Space Telescope, unveiling a new population of low-mass, faint galaxies reddened by dust produced in the stellar winds of asymptotic giant branch stars or carbon-rich Wolf–Rayet binaries.

Item Type:	Article
Uncontrolled Keywords:	5109 Space Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics; 0306 Physical Chemistry (incl. Structural); Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	IOP Publishing
Date of acceptance:	15 September 2025
Date of first compliant Open Access:	22 April 2026
Date Deposited:	22 Apr 2026 14:03
Last Modified:	22 Apr 2026 14:03
DOI or ID number:	10.3847/1538-4357/ae07db
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28434

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