REVIEW 2 major objections 2 minor 2 cited by
Dust in the Average Galaxy: Attenuation, Emission, and Opacity from $0<z<7$
T0 review · 2 major / 2 minor · reviewed 2026-06-27 · grok-4.3
Pith's one-line read The ratio of UV to far-infrared dust absorption coefficients decreases by more than an order of magnitude from redshift 0 to 7.
desk verdict The claimed order-of-magnitude drop in κ_UV/κ_FIR could be an artifact of FIR stacking selection rather than real grain evolution. 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
What carries the argument
κ_UV/κ_FIR, the ratio of dust mass absorption coefficients at 1600Å and 500μm, which separates the effects of star-dust geometry from intrinsic grain properties when combined with IR SED shape and dust mass surface density.
What would settle it
Individual ALMA detections of high-redshift galaxies that show no evolution in κ_UV/κ_FIR when their own FIR SEDs are measured directly, rather than relying on stacks.
Extended reading notes
Core claim
We measure over an order of magnitude decrease in κ_UV/κ_FIR—the ratio of dust mass absorption coefficients in the UV at 1600Å and FIR at 500μm—from z~0 to z~7, consistent with a deficit of small dust grains. UV/optical attenuation systematically underpredicts IR luminosity by a factor of ~3x at 0.5<z<7 and up to an order of magnitude for M⋆>10^10.5 M⊙. We derive empirical relationships for effective attenuation, dust temperature, unobscured star-formation fraction, and dust-to-stellar mass ratio as functions of redshift and stellar mass. A redshift-invariant inverse relationship exists between κ_UV/κ_FIR and Σ_SFR. Most evolution in the dust-to-stellar ratio occurs at z<1.
Load-bearing premise
The stacked FIR SEDs from the combined Spitzer/Herschel/SCUBA-2/NIKA-2/ALMA data accurately represent the average dust emission properties of the full 500,000-galaxy sample without significant biases from detection limits or sample selection at each redshift and mass bin.
Editorial extensions
If this is right
- UV/optical attenuation underpredicts true IR luminosity by factors of three to ten depending on redshift and stellar mass.
- Empirical scaling relations exist for attenuation, dust temperature, unobscured star-formation fraction, and dust-to-stellar mass ratio versus redshift and mass.
- κ_UV/κ_FIR maintains an inverse correlation with star-formation rate surface density that does not change with redshift.
- The bulk of the decline in dust-to-stellar mass ratio is finished by redshift one, resulting from combined changes in gas fraction and dust-to-gas ratio.
Reading between the lines
- Dust formation models must include radiation-field strength as a driver of grain-size distribution if the deficit of small grains at high redshift is real.
- Simulations assuming fixed dust optical properties will systematically understate the obscured fraction of star formation above redshift three.
- Higher-sensitivity FIR observations could determine whether the trend in κ_UV/κ_FIR continues past redshift seven or levels off.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript analyzes dust properties in over 500,000 galaxies at 0<z<7 using JWST COSMOS-Web UV/optical data combined with stacked FIR/(sub)mm SEDs from Spitzer/Herschel/SCUBA-2/NIKA-2/ALMA. It reports that UV/optical attenuation underpredicts IR luminosity by a factor of ~3 (up to 10x at M⋆>10^10.5 M⊙), derives empirical relations for effective attenuation, T_dust, unobscured SF fraction, and M_dust/M⋆ as functions of z and M⋆, and measures an order-of-magnitude drop in κ_UV/κ_FIR (1600Å to 500μm) from z~0 to z~7. This is interpreted as evidence for evolving grain properties (deficit of small grains at high z), with an inverse relation to Σ_SFR; most M_dust/M⋆ evolution occurs at z<1.
Significance. The large sample and direct UV-to-FIR comparison provide a broad empirical baseline for average-galaxy dust behavior across cosmic time. If the κ_UV/κ_FIR evolution is robust, the result would strengthen the case that grain-size distributions change with redshift and radiation-field intensity, with implications for dust models and the reliability of UV-based attenuation corrections. The work credits the scale of the JWST+FIR stacking approach for enabling population-level constraints beyond extreme starbursts.
major comments (2)
- [Abstract; FIR stacking procedure] Abstract and methods on FIR stacking: the central claim of an order-of-magnitude decrease in κ_UV/κ_FIR (and the separation of geometry from grain properties via IR SED + UV SED + dust mass surface density) assumes the stacked L_IR and T_dust values represent the full 500k-galaxy population in each z–M⋆ bin. No explicit completeness corrections, upper-limit handling, or detection-fraction statistics are described; if high-z stacks are dominated by the FIR-detectable tail, L_IR would be overestimated relative to the UV attenuation measured on the full sample, directly biasing the κ ratio downward and producing the reported trend.
- [Results on κ_UV/κ_FIR and Σ_SFR relation] Results on empirical relations: the reported redshift-invariant inverse relation between κ_UV/κ_FIR and Σ_SFR, and the claim that UV underpredicts IR by ~3× (10× at high mass), rest on post-hoc binning whose effect on the derived ratios is not quantified with error budgets or jackknife tests. This leaves open whether the dynamic range in κ_UV/κ_FIR is driven by the underlying data or by binning choices.
minor comments (2)
- [Abstract] The abstract states the factor-of-3 (and order-of-magnitude) discrepancies without accompanying uncertainties or sample-completeness notes; adding a one-sentence qualifier would improve clarity.
- [Methods on opacity derivation] Notation for κ_UV/κ_FIR is introduced without an explicit equation defining the absorption coefficients from the SED fits; a short derivation or reference to the fitting procedure would aid reproducibility.
Simulated Author's Rebuttal
We thank the referee for their careful reading and insightful comments on our manuscript. Their concerns about the FIR stacking representativeness and the robustness of the derived relations to binning choices are well-taken. We address each major comment in detail below and propose revisions to enhance the clarity and rigor of the presentation.
read point-by-point responses
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Referee: [Abstract; FIR stacking procedure] the central claim of an order-of-magnitude decrease in κ_UV/κ_FIR assumes the stacked L_IR and T_dust values represent the full 500k-galaxy population in each z–M⋆ bin. No explicit completeness corrections, upper-limit handling, or detection-fraction statistics are described; if high-z stacks are dominated by the FIR-detectable tail, L_IR would be overestimated relative to the UV attenuation measured on the full sample, directly biasing the κ ratio downward and producing the reported trend.
Authors: The FIR stacking is performed by co-adding the FIR images of all galaxies in each redshift-stellar mass bin from the full sample of over 500,000 galaxies, including those not individually detected in the FIR. This median stacking approach provides the average emission properties for the entire population in the bin. We will update the methods section to explicitly describe this procedure, include detection fraction statistics per bin, and discuss how this mitigates the potential bias raised. revision: yes
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Referee: [Results on κ_UV/κ_FIR and Σ_SFR relation] the reported redshift-invariant inverse relation between κ_UV/κ_FIR and Σ_SFR, and the claim that UV underpredicts IR by ~3× (10× at high mass), rest on post-hoc binning whose effect on the derived ratios is not quantified with error budgets or jackknife tests. This leaves open whether the dynamic range in κ_UV/κ_FIR is driven by the underlying data or by binning choices.
Authors: The binning in z and M⋆ is chosen based on achieving sufficient numbers for reliable stacking and is not post-hoc. The reported relations are robust to variations in binning as tested internally. We will add quantitative error budgets using bootstrap methods on the stacks and include jackknife resampling tests in the revised manuscript to explicitly quantify the impact of binning choices on the derived κ_UV/κ_FIR values and the UV-IR discrepancy. revision: partial
Circularity Check
No circularity: all results are direct empirical fits to stacked observational data
full rationale
The paper reports empirical measurements of attenuation, FIR SEDs, dust temperature, and the ratio κ_UV/κ_FIR derived from JWST UV/optical data combined with stacked Spitzer/Herschel/SCUBA-2/NIKA-2/ALMA FIR photometry across 500k galaxies. No equation or result is shown to reduce by construction to a parameter fitted from the same quantity; the reported order-of-magnitude evolution in κ_UV/κ_FIR is obtained by combining independent constraints on IR luminosity, UV attenuation, and dust mass surface density. Self-citations, if present, are not load-bearing for the central claims. The derivation chain remains self-contained against external data.
Assumptions & free parameters
free parameters (1)
- coefficients of empirical attenuation, T_dust, f_unobscured, and M_dust/M_star relations
Cite this review
Pith. "Pith review of Dust in the Average Galaxy: Attenuation, Emission, and Opacity from $0<z<7$." pith.science (2026). https://pith.science/paper/5LK7DU2J
@misc{pith2026260617270,
author = {Pith},
title = {Pith review of: Dust in the Average Galaxy: Attenuation, Emission, and Opacity from $0<z<7$},
year = {2026},
howpublished = {\url{https://pith.science/paper/5LK7DU2J}},
note = {Machine review of arXiv:2606.17270}
}
abstract
We present constraints on the dust emission and attenuation properties of galaxies across 0<z<7 using JWST imaging from the COSMOS-Web Survey combined with deep FIR/(sub)millimeter data from Spitzer, Herschel, SCUBA-2, NIKA-2 and ALMA. We analyze over 500,000 galaxies to independently constrain attenuation in the rest-frame UV/optical as well as dust emission from stacked FIR SEDs, enabling a direct comparison between the two. We find UV/optical attenuation systematically underpredicts IR luminosity by a factor of ~3x at 0.5<z<7 and up to an order of magnitude for $M_\star>10^{10.5}M_\odot$. We derive empirical relationships for the effective attenuation, dust temperature, fraction of star formation that is unobscured, and dust-to-stellar mass ratio as functions of redshift and stellar mass. We separate the first order effect of star/dust geometry from dust grain properties by combining constraints on the IR SED, UV SED, and dust mass surface density. Importantly, we measure over an order of magnitude decrease in $\kappa_{UV}/\kappa_{FIR}$--the ratio of dust mass absorption coefficients in the UV at 1600\AA\ and FIR at 500$\mu$m--from z~0 to z~7. A depressed $\kappa_{UV}/\kappa_{FIR}$ is consistent with a deficit of small dust grains, possibly attributable to the intense radiation fields of high-$z$ star formation; indeed, we find a redshift-invariant inverse relationship between $\kappa_{UV}/\kappa_{FIR}$ and $\Sigma_{SFR}$. Most evolution in the dust-to-stellar ratio is at $z<1$, the product of mild downward evolution in the dust-to-gas ratio combined with steep evolution in the gas-to-stellar ratio. The significant evolution and dynamic range of $\kappa_{UV}/\kappa_{FIR}$ and prevailing disconnect between the UV/optical and FIR regimes emphasize that direct dust constraints are irreplaceable for the majority of star-forming galaxies at z<7, not just the most extreme star-formers.
Figures
Figures from the paper (38 more)
Forward citations
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Far-infrared observations of dust in Ly$\alpha$ emitters at z=2-6
Far-IR stacking of ~4000 LAEs at z=2-6 yields detections in massive AGN hosts with low f_esc(Lyα) (1-7%) and higher values (>10%) in undetected stacks, plus elevated IRX relative to typical star-forming galaxies.
Reviewed June 27, 2026 · model on record in the stance chip above.
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