REVIEW 1 cited by
Unveiling the Dark Side of UV/Optical Bright Galaxies: Optically Thick Dust Absorption
T0 review · reviewed 2026-08-12 · deepseek-v4-flash
Pith's one-line read One-third of massive galaxies at z~3 host optically thick dust substructures that hide 10-20% of their stellar mass and star formation rate.
desk verdict First census of patchy optically thick dust at z~3 with a clean out-of-sample F444W detection, but the mass/SFR fractions are model-dependent and the claimed lower-limit direction is not safe. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
For those candidate galaxies, the authors subtracted the model image from the observed image to locate the dusty patches, then fit the light of each patch separately. They estimate that these patches contain about 10-20% of the stars and star formation in these galaxies, and that the obscured fraction does not depend strongly on galaxy mass or star formation rate. The patches are often off-center and irregular, and galaxies with a recent burst of star formation in the last 100 million years tend to have more hidden light. The main caveat is that the conversion from extra red light to hidden mass assumes the hidden regions emit like the rest of the galaxy, and any contribution from black holes (AGN) is ignored, so the true numbers could be lower or higher.
Extended reading notes
Core claim
Around one-third of the massive galaxies at z~3 show evidence of optically thick dust obscuration, which segregates on average ~10-20% of the stellar mass and SFR, i.e. they are invisible to UV/optical observations (Section 7). If correct, standard SED-based mass and SFR estimates for massive galaxies at cosmic noon are systematically low by this amount in a third of the population.
Load-bearing premise
The assumption, stated in Section 2 and used in Section 5.1, that the intrinsic spectral shapes of the optically thin and optically thick components are identical. Under this assumption, the F444W excess directly maps to obscured stellar mass and SFR using the same mass-to-light ratio as the rest of the galaxy. If the hidden regions are actually younger (as the burstiness correlation suggests) or contain AGN light, the mass-to-light ratio differs and the quoted 10-20% obscured fractions shift. The paper acknowledges this and calls its estimates lower limits.
Editorial analysis
A structured set of objections, weighed in public.
Assumptions & free parameters
free parameters (2)
- Candidate selection threshold in F444W excess =
15 sigma
- SFH binning and continuity prior =
7 lookback bins, reduced to 5 for substructures
assumptions (5)
- ad hoc to paper Intrinsic spectral shapes of optically thin and optically thick components are identical
- ad hoc to paper The F444W excess is entirely attributed to dust-obscured star formation, not AGN
- domain assumption Calzetti et al. (2000) attenuation law applies to all galaxies and substructures
- domain assumption F444W-band dust optical depth is less than unity for the searched regions
- domain assumption Parent sample selection via EAZY photo-z and stellar mass is accurate enough
Cite this review
Pith. "Pith review of Unveiling the Dark Side of UV/Optical Bright Galaxies: Optically Thick Dust Absorption." pith.science (2026). https://pith.science/paper/TPQ3QKM5
@misc{pith2026241108100,
author = {Pith},
title = {Pith review of: Unveiling the Dark Side of UV/Optical Bright Galaxies: Optically Thick Dust Absorption},
year = {2026},
howpublished = {\url{https://pith.science/paper/TPQ3QKM5}},
note = {Machine review of arXiv:2411.08100}
}
read the original abstract
Over the past decades, a population of galaxies invisible in optical/near-infrared, but bright at longer wavelengths, have been identified through color selections. These so-called optically faint/dark galaxies are considered to be massive quiescent galaxies or highly dust-attenuated galaxies. Having the entire galaxy obscured by dust, however, is likely an extreme case of the much more common occurrence of optically thin and thick absorption coexisting in the same system. With the power of JWST imaging, we are able to spatially resolve massive galaxies at z~3, accurately model their spectral energy distributions, and identify candidate optically thick substructures. We target galaxies with log(M*/Msun)>10.3 and 2.5<z<3.5, and get 486 galaxies in CEERS and PRIMER fields. Based on excess NIR luminosity, we identify 162 galaxies (~33\% of the parent sample) as candidate hosts of optically thick substructures. We then carry out spatially resolved SED modeling to explore the physical properties of those dark substructures and estimate the amount of optically thick obscuration. We find that optically thick dust is ubiquitous in normal massive galaxies with a wide variety of SFR and morphology. 10-20\% of the stellar mass/SFR are unaccounted for in our selected galaxies, and the fraction is insensitive to stellar mass or SFR. The dark substructures are generally dustier than the rest of the galaxies and are irregularly distributed, arguing against an obscured AGN as the source of the NIR excess. A correlation between the obscured luminosity and the presence of a recent starburst in the past <100 Myr is also observed.
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Forward citations
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The CEERS survey overview shows that coordinated parallel JWST observations in the EGS field work as designed and have generated a public legacy dataset that enabled extensive early-universe science.
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Reviewed August 12, 2026 · model on record in the stance chip above.
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