{"id":"b41151e1-d113-4b72-9f69-a197f3cdf29e","arxiv_id":"2501.02956","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"The median Sérsic index changes little with redshift except for the most massive galaxies, with near-infrared structure depending strongly on star-formation activity but not stellar mass at z>1.","lead":"Using JWST near-infrared images of about 15,000 galaxies, this paper measures how concentrated galaxy light is and how that changes from redshift 2.5 to today. It finds that the shape of most galaxies stays roughly constant over time, except the most massive ones, and reports two new trends linking galaxy structure to star formation.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The optical-vs-NIR Sérsic-index comparison rests on two mostly disjoint galaxy samples; stellar masses/SFRs are validated on the ~10% overlap, but the Sérsic indices themselves are not, so the wavelength-dependence claim may be dominated by survey and fitting-pipeline offsets.","rationale":"The reader's weakest-assumption analysis identifies exactly the same load-bearing risk: the optical and near-IR Sérsic indices come from different surveys with only about 10% overlap, and the paper validates stellar population parameters but not the morphology measurements on the common subset. I agree that this is the most serious threat to the central argument because the paper's most distinctive new claim, the wavelength dependence of n and its attribution to star-forming galaxies at z>1, is a cross-sample comparison. The test I propose would settle the issue directly: measure n0.5 and n1.5 on the same galaxies in the overlap and check whether the median offset seen in the full samples is reproduced. If it is, the claim gains strong support; if not, the comparison is unreliable. This concern is addressable and does not by itself overturn the other conclusions, so the reader's CONDITIONAL verdict remains appropriate; no change to the verdict is needed, but the condition should explicitly require the overlap-based validation of Sérsic indices or an equivalent matched-sample analysis.","tokens_in":22902,"tokens_out":6055,"duration_ms":60457,"concrete_test":"Restrict the analysis to the overlapping galaxies in COSMOS where both HST/CANDELS and JWST NIRCam imaging exist; measure n0.5 and n1.5 for the same galaxies with the respective pipelines, then compare the median difference (n0.5 - n1.5) in stellar-mass/redshift bins, especially for star-forming galaxies at z>1. If the overlap subset reproduces the full-sample offset (n0.5 < n1.5 for SF galaxies at z>1), the wavelength claim is robust; if the offset disappears or changes sign, it is a selection or calibration artifact. A complementary sanity check would be to run the HST fitting pipeline on the JWST images, or vice versa, on the overlap sample to separate code/PSF systematics from true wavelength dependence.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's most novel result is the wavelength dependence of the Sérsic index: at z>1, star-forming galaxies have lower rest-frame optical (0.5 micron) than near-IR (1.5 micron) n. This claim is built by comparing n0.5 from the HST/CANDELS sample (five fields, Galfit fits to F125W/F160W) with n1.5 from the JWST/COSMOS-Web+PRIMER sample (COSMOS field, GalfitM fits to F277W/F444W). Section 2.2 states that only ~10% of the JWST sample was observed by HST/CANDELS. Appendix A validates stellar masses and SFRs for the 1,656 overlapping galaxies, but it does not validate the Sérsic indices themselves. Thus the central comparison assumes that median n from the two instruments, filters, fitting codes, PSF models, and parent photometric catalogs are statistically interchangeable. Differences in selection functions, field-to-field cosmic variance, wavelength-dependent PSF modeling, and fit constraints can all shift n in a redshift- and mass-dependent way, mimicking a physical optical-vs-NIR offset. Because the other main trends (slow redshift evolution, mass dependence) appear within each sample separately, the cross-sample wavelength comparison is the most load-bearing element: if the two pipelines are not equivalent, the claim that the offset is caused specifically by star-forming galaxies at z>1 fails, even though the evolution of n with redshift and mass may survive.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper measures rest-frame 1.5 micron Sérsic indices for approximately 15,000 galaxies in the COSMOS-Web and PRIMER-COSMOS fields with JWST/NIRCam and combines them with previously published rest-frame 0.5 micron Sérsic indices from HST/CANDELS. Over 0.510^11 Msun) increase from n~2.5 at z=2.5 to n~4 at z<1. They further report that star-forming galaxies have lower optical than near-IR n at z>1 but not at z<1, that at z>1 near-IR n depends strongly on specific star formation rate but not on stellar mass, and that the scatter in near-IR n peaks in the green valley. The paper provides tabulated medians and percentiles and fits the redshift evolution with a power-law n ∝ (1+z)^beta.","tokens_in":23208,"tokens_out":5980,"duration_ms":57215,"significance":"If the results are robust, this is a valuable empirical benchmark: it extends structural measurements to rest-frame near-IR at cosmic noon with a sample an order of magnitude larger than previous JWST studies, and it provides tabulated data that can be used to test simulations. Strengths include the careful documentation of sample cuts, bootstrap-resampled fits, the use of a consistent Prospector setup for stellar masses and SFRs across the two samples, and the explicit Appendix B data tables. The main novel claim, the optical-near-IR wavelength dependence among star-forming galaxies at z>1, rests on a cross-survey comparison that is not yet validated; if that validation succeeds, the paper makes a strong case that dust and stellar-population gradients affect optical profiles more than near-IR profiles.","major_comments":[{"comment":"The claim that at z>1 star-forming galaxies have lower rest-frame 0.5 micron than 1.5 micron Sérsic indices is built on comparing two largely disjoint samples: the HST/CANDELS sample fitted with Galfit and the JWST/COSMOS-Web+PRIMER sample fitted with GalfitM, using different filters, PSF models, and parent photometric catalogs. Appendix A validates stellar masses and SFRs for the 1,656 overlapping galaxies, but it does not validate the Sérsic indices themselves. A systematic offset in n between the two pipelines that depends on redshift, mass, or galaxy type would directly produce or erase the reported wavelength dependence. The authors should compare Sérsic indices measured from HST and JWST imaging for the same galaxies (e.g., n from F160W vs. n from F277W), or otherwise demonstrate that the pipeline differences do not affect the median n difference, before the wavelength-dependence result can be considered secure.","section":"Sections 2.2 and Appendix A"},{"comment":"The new result that at z>1 the median near-IR Sérsic index depends on sSFR but not on stellar mass is stated qualitatively. The figure shows spline-quantile regressions and medians, but no quantitative measure of the strength of the mass dependence at fixed sSFR (e.g., a fitted slope of n1.5um versus log M* in narrow sSFR bins, with uncertainties). Without such a measure, the absence of a mass dependence is not demonstrated; the reader cannot tell whether the apparent flatness is consistent with, say, a 0.3 dex change in n across the mass range. Adding this quantification would make the claim testable.","section":"Section 3.2, Figure 4"},{"comment":"The decisions to retain flag=1 galaxies and to clip n to the [0.2,8] range are justified with summary statements (the sample is not biased; medians change by <4%) but no supporting diagnostics are shown. If the flag=1 galaxies or the clipped galaxies are concentrated in particular mass-redshift bins (e.g., the highest masses, where fits are most difficult), these choices could affect exactly the bins that drive the reported high-mass evolution and the near-IR/optical difference. The authors should provide the fraction of flag=1 and clipped sources per mass-redshift bin, or repeat the key analyses excluding these sources.","section":"Section 2.1"}],"minor_comments":[{"comment":"The text uses '≈ 15.000' with a period as the thousands separator; these should be '≈15,000'.","section":"Abstract and Section 1"},{"comment":"The caption for the right panel reads 'rest-frame 0.5µm (left panel)'; it should say 'right panel'.","section":"Figure 2 caption"},{"comment":"The sentence 'These differences do not play a major role in this work' would benefit from a quantitative justification, especially because SFR differences up to 0.6 dex could shift galaxies across the adopted quiescence boundary.","section":"Appendix A"},{"comment":"The statement that 'conclusions based on observations such as those presented in this paper will always remain speculative' is vague and could be replaced with a more specific caveat about the limitations of Sérsic fits and projection effects.","section":"Section 4"}],"recommendation":"major_revision","confidential_remarks":"The paper is a solid empirical study and the new near-IR catalog is valuable. The key issue is the unvalidated cross-sample Sérsic index comparison; I would ask the authors to perform a direct comparison of HST- and JWST-based Sérsic indices for the overlapping galaxies. If the wavelength dependence survives this test, the paper is likely acceptable. I also note that the authors rely heavily on their own prior catalogs; this is natural but should be acknowledged with appropriate detail."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: this is a solid empirical paper that delivers the largest rest-frame near-IR Sérsic index sample at 0.51 and the elevated scatter in the green valley. The central trends are probably right; the wavelength-dependence claim is the part I would push back on.\n\nWhat it does well: the sample construction is transparent and careful. SNR>50 cut, flag handling, boundary clipping, and bootstrap fitting for beta exponents are all documented. The mass completeness argument is standard. The most robust result is that median n is flat with redshift up to M*=10^10.5, and that holds in both optical and near-IR within each sample separately. The sSFR-n plane analysis is thoughtful, especially the point that the mass dependence at fixed sSFR disappears at z>1 and that the apparent mass dependence in Fig. 1 is driven by the bending of the SFMS.\n\nThe soft spots. First, the optical-vs-NIR comparison, which underlies the claim that star-forming galaxies have lower optical than near-IR n at z>1, is built on two samples with only ~10% overlap. Appendix A validates stellar masses and SFRs on the overlap, but not the Sérsic indices themselves. Different instruments, filters, fitting codes (Galfit vs GalfitM), PSF models, and parent catalogs can all shift n in redshift- and mass-dependent ways. The paper would be much stronger if they fit both rest-frame optical and near-IR for the same overlapping galaxies and showed the offset directly. This is a specific, addressable issue, not proof the result is wrong.\n\nSecond, the abstract presents the green-valley scatter (0.25 vs 0.18 dex) as a firm result, but in Section 3.2.1 the authors themselves say the peak is less clear at z>1 and 'remains to be seen' whether it's physical. That caveat should be in the abstract or the claim should be downgraded to z<1 only.\n\nWho should read it: anyone working on galaxy structure at cosmic noon. The tabulated medians in Appendix B are a useful resource. The slow-evolution result is likely to survive, and even if the wavelength comparison is later shown to be partly pipeline-driven, the data and the main trends are worth publishing.\n\nRecommendation: send to a serious referee. Ask for a direct cross-validation of n on the overlapping galaxies, or a softened wavelength claim, and align the abstract with the body on the green valley.","headline":"Solid empirical step forward on near-IR Sérsic indices; the slow-evolution result is probably safe, but the optical-vs-NIR wavelength claim rests on a thin cross-survey comparison and the abstract overstates the green-valley scatter.","tokens_in":23887,"tokens_out":4876,"would_cite":true,"duration_ms":121563,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"The median Sérsic index of galaxies barely changes from z=2.5 to z=0.5, except for the most massive galaxies, whose profiles steepen from n≈2.5 to n≈4 by z<1.","keywords":["Sérsic index","galaxy structure","galaxy evolution","rest-frame near-infrared","JWST","NIRCam","star formation","quiescent galaxies"],"falsifier":"Measure rest-frame 0.5 µm and 1.5 µm Sérsic indices for the same galaxies, using the roughly 10% of JWST sources with HST/CANDELS coverage or a single survey covering both wavelengths, and check whether the $n_{1.5\\,\\mu m} > n_{0.5\\,\\mu m}$ offset for star-forming galaxies at $z>1$ persists; if it vanishes, the claimed wavelength dependence is a sample-selection artifact.","tokens_in":22677,"feed_emoji":"🔭","tokens_out":6745,"duration_ms":59770,"temperature":0.7,"pith_summary":"This paper measures how the radial concentration of galaxy light, quantified by the Sérsic index $n$, changes between redshift 2.5 and 0.5, using JWST near-infrared images of about 15,000 galaxies combined with HST optical images of a similar sample. It argues that, at fixed stellar mass below about $10^{10.5}\\,M_\\odot$, the median Sérsic index barely changes over roughly 11 billion years: galaxies keep approximately exponential profiles at all redshifts studied. The exception is the most massive galaxies ($M_\\star > 10^{11}\\,M_\\odot$), whose median $n$ rises from about 2.5 to about 4 toward $z<1$. The paper also establishes that star-forming galaxies have lower $n$ than quiescent galaxies in both optical and near-infrared light, and that at $z>1$ the near-infrared $n$ depends on star-formation activity but not on stellar mass. These results matter because they tie the buildup of central concentrations to mass and quenching, and provide near-infrared light profiles that simulations can compare directly with stellar mass profiles.","feed_headline":"Most galaxy light profiles stay fixed for 11 billion years","feed_subtitle":"Only the heaviest galaxies grow steeper, more concentrated profiles after z=1.","key_machinery":"The central object is the Sérsic index $n$, the shape parameter of the Sérsic profile $I(r)\\propto \\exp[-b_n(r/r_e)^{1/n}]$, with $n=1$ exponential-like and $n=4$ de Vaucouleurs-like. The argument is carried by comparing two rest-frame measurements on HST-selected parent samples: $n$ at 0.5 µm from HST/CANDELS F125W/F160W fits and $n$ at 1.5 µm from JWST/NIRCam F277W/F444W fits in COSMOS-Web and PRIMER-COSMOS, interpolated to the rest-frame wavelengths. Stellar masses, star-formation rates, and the quiescent/star-forming classification come from SED fitting and an offset from the star-forming main sequence; redshift evolution is characterized with fits $n_\\lambda \\propto (1+z)^{\\beta_\\lambda}$. The load-bearing comparison is the difference between the two rest-frame indices for the same mass-redshift bins.","core_discovery":"The paper's central claim is that the rest-frame near-infrared Sérsic index, measured at 1.5 µm with JWST/NIRCam, is a stable structural parameter for most galaxies: for stellar masses below about $10^{10.5}\\,M_\\odot$ the median $n \\approx 1.4$ at all redshifts from 0.5 to 2.5, and the same holds in the rest-frame optical at 0.5 µm. Only galaxies with $M_\\star > 10^{11}\\,M_\\odot$ show significant evolution, increasing from $n\\approx 2.5$ at $z\\approx 2.5$ to $n\\approx 4$ at $z<1$, with the optical index evolving more strongly with redshift than the near-IR index. The higher near-IR than optical $n$ for star-forming galaxies at $z>1$ is attributed to radially varying dust and young-star outshining in the optical, while the structural distinction between quiescent and star-forming galaxies persists in the near-IR, implying a physical difference in stellar mass distribution rather than a mere light-profile artifact. Two trends are new: at $z>1$ the median near-IR $n$ tracks specific star-formation rate without any mass dependence, and the scatter in near-IR $n$ peaks in the green valley (0.25 dex) versus 0.18 dex elsewhere, a peak hidden in the optical by dust and young stars.","pith_inferences":["If the near-IR index stays constant at fixed mass while sizes grow, then the observed size evolution of low-mass galaxies must be driven by mass growth along a fixed concentration, which would shift the interpretation of the size-mass relation from structural transformation to assembly.","The wavelength-dependent $n$ for massive star-forming galaxies implies that scaling relations built on optical concentration (for example, black-hole–bulge relations) may be systematically biased at $z>1$; near-IR-based relations should be tested.","A direct test of the sample-equivalence assumption would be to measure both rest-frame indices for the same galaxies in the roughly 10% overlap region, or to use JWST filters that cover rest-frame optical at $z>3$ to trace when the mass dependence of $n$ first appears.","The green-valley scatter peak suggests that structural diversity could be used to separate quenching mechanisms, such as mergers versus feedback, in future samples with kinematic or environmental data."],"forward_implications":["Below $M_\\star\\approx10^{10.5}\\,M_\\odot$, the radial light profiles of galaxies are essentially in place by $z=2.5$; subsequent evolution is mostly growth in stellar mass along a constant $n$, not a transformation of the profile.","The late-time rise in $n$ for $M_\\star>10^{11}\\,M_\\odot$ means the most massive galaxies build their concentrated central profiles at $z<1$, plausibly through dissipationless merging and central growth.","Rest-frame near-IR $n$ is a cleaner proxy for the stellar mass profile than optical $n$; optical measurements of massive star-forming galaxies at $z>1$ are flattened by dust and young stars.","The elevated scatter in near-IR $n$ in the green valley indicates that the transition from star-forming to quiescent is structurally diverse, with multiple possible pathways.","The tabulated $n_{1.5\\,\\mu m}$ measurements give simulations a direct observable to match for radial stellar mass profiles."],"supporting_citations":[{"why":"Provides the HST/CANDELS Sérsic fits and the signal-to-noise calibration that define the rest-frame optical sample.","marker":"van der Wel et al. (2012)"},{"why":"Supplies stellar masses, redshifts, and star-formation rates from SED fitting, plus the star-forming main sequence ridge used for classification.","marker":"Leja et al. (2020)"},{"why":"Companion paper providing the JWST/NIRCam F277W and F444W Sérsic fits from which the rest-frame near-IR indices are taken.","marker":"Martorano et al. (2024)"},{"why":"Defines the COSMOS-Web survey whose NIRCam mosaics supply part of the near-IR sample.","marker":"Casey et al. (2023)"},{"why":"Defines the PRIMER-COSMOS survey whose NIRCam mosaics supply the other part of the near-IR sample.","marker":"Dunlop et al. (2021)"},{"why":"Earlier measurement of the mass dependence of the Sérsic index that this paper extends and compares with.","marker":"Lang et al. (2014)"},{"why":"Provides the earlier $n \\propto (1+z)^{\\beta}$ redshift-evolution parametrization that this paper directly compares with its own fitted exponents.","marker":"Patel et al. (2013)"}],"fun_headline_variants":["Most galaxies keep their light profile for 11 billion years","Galaxy shapes stable for most, only giants steepen","JWST: Sérsic index flat for most galaxies since z=2.5","Only the heaviest galaxies evolve their light profiles"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The optical and near-IR samples come from different surveys with only about 10% overlap, so the comparison assumes the two samples are statistically equivalent populations at fixed mass, redshift, and star-formation activity.","fun_headline_variants_meta":{"raw":{"variants":["Most galaxies keep their light profile for 11 billion years","Galaxy shapes stable for most, only giants steepen","JWST: Sérsic index flat for most galaxies since z=2.5","Only the heaviest galaxies evolve their light profiles"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000316,"raw_usage":{"total_tokens":1951,"prompt_tokens":1267,"completion_tokens":684,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":883,"completion_tokens_details":{"reasoning_tokens":613}},"tokens_in":883,"tokens_out":684,"duration_ms":6959,"temperature":1.0,"reasoning_tokens":613,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T21:59:11.502936+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure rest-frame 0.5 µm and 1.5 µm Sérsic indices for the same galaxies, using the roughly 10% of JWST sources with HST/CANDELS coverage or a single survey covering both wavelengths, and check whether the $n_{1.5\\,\\mu m} > n_{0.5\\,\\mu m}$ offset for star-forming galaxies at $z>1$ persists; if it vanishes, the claimed wavelength dependence is a sample-selection artifact.","supporting_citations":[{"cited_title":"G., van Dokkum , P","cited_arxiv_id":null,"evidence_quote":"Provides the earlier $n \\propto (1+z)^{\\beta}$ redshift-evolution parametrization that this paper directly compares with its own fitted exponents."}],"review_version":1}