{"id":"b58c20de-001a-4522-9109-bc3cbbd80ff3","arxiv_id":"2501.01207","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Progenitors of today's green valley galaxies in EAGLE grow gas-rich, then merge and interact, then quench through environment and mass, with most entering the green valley only at z<1.","lead":"Using the EAGLE supercomputer simulation, this paper traces the ancestors of today's green valley galaxies, the in-between population of galaxies that are shutting down star formation, back to when the universe was 500 million years old. It finds a three-phase history: early black hole regulation, middle mergers, and late environmental shutdown, with most galaxies entering the green valley only in the last few billion years.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The z<1 entry-time and ~5% rejuvenation results depend on an unstated higher-redshift GV classification; specification and a redshift-dependent test are required.","rationale":"The reader's weakest_assumption is exactly the missing higher-redshift classification, and I agree that it is the key soft spot. The paper is otherwise transparent: EAGLE data, mass cuts, Otsu/entropic method at z=0, progenitor tracking, and a stated caveat on the M*>=8.3 cut. The three-phase narrative is broadly consistent with the literature and is not the main risk. The numbers from Figure 19, however, are not reproducible because the text never defines 'entered the green valley' or 'crossed the green valley' at z>0. This is not a disagreement with consensus; it is an internal specification gap in the method. A fixed-threshold interpretation is the most natural reading, but it carries a strong physical assumption (redshift-invariant GV locus), while a recomputed-threshold interpretation would change the meaning of the statistics. Either way, the central quantitative claims need clarification and a robustness test. I therefore keep CONDITIONAL, matching the reader's verdict, since the issue is addressable without invalidating the overall EAGLE-based analysis. I also note that no formal verification or released code is provided, so the reproducibility check is especially warranted.","tokens_in":20391,"tokens_out":1611,"duration_ms":14213,"concrete_test":"Re-derive Figure 19 twice: (1) apply the z=0 thresholds s1(M*), s2(M*) to all snapshots; (2) recompute entropic thresholds independently at each snapshot's colour-mass distribution. If the 'entered at z<1' fraction or the 'crossed by z=0.1' fraction changes by more than ~10% relative between these two prescriptions, the headline depends on the unspecified higher-z classification. Additionally, check the ~5% crossed-branch sample directly: for each such branch, inspect its SFR and (u-r) colour trajectory between z=0.1 and z=0 to confirm rejuvenation (SFR rising above a quiescent threshold) rather than a threshold artifact.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The quantitative headline results, Figure 19 and the abstract's claim that most main progenitor branches entered the GV at z<1 and ~5% crossed into the red sequence by z=0.1, depend entirely on classifying progenitor galaxies as 'in the green valley' at redshifts z>0. The paper only describes a z=0 classification (Section 2.2): entropic thresholding in (u-r) colour, binned in stellar mass, giving thresholds s1(M*) and s2(M*). Sections 3.5 and the text surrounding Figure 19 never state whether these z=0 thresholds are applied unchanged to higher-redshift snapshots, or whether the classification is recomputed per snapshot. If the z=0 thresholds are applied at all redshifts, the classification assumes the GV colour locus is redshift-invariant in (u-r) at fixed stellar mass. This is unlikely to be exactly true: the blue cloud and red sequence evolve with redshift, and at z>2 the sample is restricted to M*>=10^8.3 Msun progenitors whose (u-r) colours may be noisy or systematically offset. If instead the thresholds are recomputed per snapshot, the track-back is not defined by the text, and the 'entered at z<1' statistic has no stated operational meaning. Either way, the ~50% and ~5% numbers are not reproducible from the paper as written. This is load-bearing because those numbers are the paper's central quantitative findings and the basis for the late-time rejuvenation claim.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper uses the EAGLE Ref-L0100N1504 simulation to trace the progenitors of present-day green valley (GV) galaxies, identified at z=0 via the entropic-thresholding method of Pandey (2024), from z=10 to z=0. It reports a three-phase evolutionary picture: an early growth phase (z=10-6) with gas-rich, star-forming progenitors regulated by AGN feedback; a transition phase (z=6-2) marked by frequent interactions and mergers in denser environments; and a quenching phase (z=2-0) dominated by environmental and mass-dependent processes with rapid cold gas depletion. The paper's headline quantitative claims are that most main progenitor branches enter the green valley at z<1 and that about 5% of the branches had already crossed into the red sequence by z=0.1, which the authors interpret as evidence for late-time rejuvenation.","tokens_in":20641,"tokens_out":3239,"duration_ms":35623,"significance":"If the quantitative claims are robust, the paper offers a useful time-resolved account of how today's green valley galaxies assemble, using a widely used simulation and a data-driven colour classification that avoids arbitrary cuts. The qualitative trends in AGN fraction, interaction fraction, SFR, cold gas content, and local density are presented clearly and do support a broad three-phase narrative. The authors also deserve credit for explicitly acknowledging the stellar-mass cut caveat and for making the analysis reproducible in principle from public EAGLE data. However, the two most quantitative findings (majority entering at z<1; ~5% rejuvenation) are not reproducible from the text because the higher-redshift classification of progenitor branches is never specified; this is a load-bearing gap that must be fixed before the central claims can be evaluated.","major_comments":[{"comment":"The classification of main progenitor branches as 'in the green valley' or 'crossed the green valley' at z>0 is never defined. Section 2.2 describes a z=0 classification using thresholds s1(M*) and s2(M*) obtained by entropic thresholding, but the text does not state whether these same thresholds are applied unchanged to higher-redshift snapshots, whether the thresholds are recomputed per snapshot, or whether some redshift-dependent colour correction is applied. If the z=0 thresholds are used at all redshifts, the analysis assumes the green valley colour locus in (u-r) at fixed stellar mass is redshift-invariant, which is unlikely to be exactly true and could systematically bias the 'entry time' statistic. If thresholds are recomputed per snapshot, the operational meaning of 'entered at z<1' is not defined. Either way, the ~50% and ~5% numbers in Figure 19 and the abstract are not reproducible from the paper as written. Please specify the procedure and provide a robustness test, for example by recomputing the thresholds at each snapshot or by applying a redshift-dependent colour-evolution correction, and show how the entry-time distribution changes.","section":"3.5 (Figure 19)"},{"comment":"The inference of late-time rejuvenation for the ~5% of branches that 'crossed' the green valley by z=0.1 rests entirely on a two-redshift classification comparison. A branch classified as red at z=0.1 and green at z=0 could be affected by threshold scatter, colour measurement noise, or a temporary fluctuation rather than a genuine rejuvenation event. The paper should validate this claim by tracking the actual SFR or specific SFR evolution of these branches and by showing that the fraction of branches with an SFR increase between z=0.1 and z=0 is consistent with the 5% estimate. Without such a check, the rejuvenation interpretation is not stronger than the classification artifacts that the unspecified higher-redshift procedure may introduce.","section":"3.5 (Figure 19) and Section 4"},{"comment":"The acknowledged stellar-mass cut log(M*/Msun) >= 8.3 is especially relevant to Figure 19 because high-redshift progenitors are systematically less massive, so the sample of branches tracked at z>2 is increasingly incomplete. The paper states the caveat but does not quantify its impact on the entry-time distribution. Please state explicitly whether the percentages in Figure 19 are computed only over branches that are resolved (and hence have colours) at each redshift, and provide a test of how the 'entered at z<1' fraction changes when the mass cut is varied within the resolved range. This is needed to assess whether 'majority enter at z<1' is a physical result or a selection effect.","section":"Section 4 (caveats)"}],"minor_comments":[{"comment":"The title line in the manuscript reads 'T racing the evolution' (missing 'h'); please correct the typo. The abstract also contains several missing spaces and inconsistent hyphenation, which should be cleaned up.","section":"Title and Abstract"},{"comment":"The axis label 'log(25 Mpc3)' in Figures 13 and 14 appears garbled; it should presumably read log(eta/(25 Mpc^-3)) or similar. Please correct the units notation and verify the density unit convention is defined consistently with Equation (2.5).","section":"Section 3.4 (Figures 13-15)"},{"comment":"The caption says 'rectengular boxes' and 'suppression the formation'; please correct these typos. Also, the two upper panels have labels of log(Mstellar/Msun) that are inconsistent (e.g., '11.6229' vs '10.6193'); please check the formatting.","section":"Section 3.5 (Figure 18 caption)"},{"comment":"The text says 'Te structure of the paper is as follows' (missing 'h'); please correct.","section":"Section 1"}],"recommendation":"major_revision","confidential_remarks":"The paper is a galaxy-evolution study; whether JCAP is the most fitting venue is an editorial judgment, but the scientific content is appropriate for an astro-ph.GA journal. The key issue is fixable: the authors must specify and test the higher-redshift classification procedure behind Figure 19. If they can show robustness to reasonable choices, the paper could be acceptable; without it, the headline quantitative claims remain unsupported."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Worth engaging. The paper is a solid, readable EAGLE analysis that tracks the progenitors of present-day green valley (GV) galaxies from z=10 to z=0 and presents a clean three-phase picture: an early AGN-regulated growth phase, a mid-epoch of interaction-driven starbursts and gas depletion, and a low-z quenching phase dominated by environment and mass. The use of entropic thresholding to define the GV in the colour-mass plane, combined with full progenitor-branch tracking, is new in this combination, and the z=0 classification is transparent enough to re-implement. The qualitative results—AGN fraction declining from ~12% at z=10 to ~2% at z=0, interactions peaking around z~2, cold gas dropping steeply at z<1—are all shown with error bars and support the narrative. The entry-time distribution in Figure 19 has not appeared before, and it is the most interesting panel in the paper.\n\nThe soft spot is exactly where the stress-test lands. The headline quantitative claims—that most main branches enter the GV at z<1 and that ~5% had already crossed into the red sequence by z=0.1—require classifying progenitors at z>0, but Section 2.2 describes only a z=0 classifier. There is no statement of whether the z=0 thresholds are applied unchanged at every snapshot, or whether the classification is recomputed per redshift. That matters. If the z=0 (u-r) boundaries are applied at all z, the method assumes the GV locus is redshift-invariant at fixed stellar mass, which is unlikely to be exactly true and needs a test. If the thresholds are recomputed per snapshot, the paper needs to say so and define how 'entered' is measured. As written, the two numbers are not reproducible. The 'must have rejuvenated' phrasing in Section 3.5 is also too strong: two snapshots can produce that inference, but a red-to-green change between z=0.1 and z=0 is a plausible rejuvenation candidate, not a necessity without checking classification errors or branch tracking.\n\nNone of this is fatal. The qualitative three-phase narrative does not depend on the missing classification, and the authors are upfront about the M*>=8.3 cut bias, even if they don't quantify it. I would send this to a referee. A referee should push for the higher-z classification, soften or defend the rejuvenation claim, and request the analysis code be released. With those addressed, the paper is a useful consolidation of GV assembly in EAGLE.","headline":"Solid, publishable EAGLE progenitor-tracking study; the headline z<1 entry-time and ~5% rejuvenation numbers are not reproducible until the higher-redshift GV classification is specified.","tokens_in":21243,"tokens_out":3522,"would_cite":true,"duration_ms":34889,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper uses the EAGLE cosmological simulation to trace the ancestors of today's green valley galaxies from redshift 10 to the present, arguing that most of them entered the green valley only at z < 1 and that a small fraction crossed…","keywords":["green valley galaxies","galaxy quenching","EAGLE simulation","galaxy evolution","entropic thresholding","merger trees","star formation","galaxy environment"],"falsifier":"Recompute the 'entered' and 'crossed' fractions using redshift-dependent green valley boundaries derived from each snapshot's own colour–mass diagram, or from observed colour distributions at $z=1$, $0.5$, and $0.1$; if the majority-entry-at-$z<1$ result or the $\\sim 5\\%$ crossing fraction changes materially, the fixed $z=0$ threshold is responsible.","tokens_in":20103,"feed_emoji":"🌌","tokens_out":8185,"duration_ms":68679,"temperature":0.7,"pith_summary":"The paper asks when and how today's green valley galaxies—those caught between the blue cloud of star-forming galaxies and the red sequence of quiescent ones—got there. Using the EAGLE cosmological hydrodynamical simulation, the authors trace the full progenitor histories of present-day green valley galaxies back to $z=10$ and identify three evolutionary phases: gas-rich growth with AGN regulation at $z=10$–$6$, interaction- and merger-driven transition at $z=6$–$2$, and environment- and mass-dominated quenching at $z=2$–$0$. The central quantitative claim is that most main progenitor branches of present-day green valley galaxies entered the green valley only at $z<1$, and that about $5\\%$ of branches had already crossed into the red sequence by $z=0.1$, implying late-time rejuvenation. The study matters because it makes the green valley a late-assembled, dynamically assembled population rather than a single universal path through colour space.","feed_headline":"Most green valley galaxies arrive late, and some bounce back","feed_subtitle":"Tracing green valley ancestry from redshift 10 to today reveals three quenching phases and a 5% late rejuvenation path.","key_machinery":"The central machinery is entropic thresholding applied to the $(u-r)$ colour–stellar mass plane at $z=0$, which produces mass-dependent green valley boundaries $s_1(M_\\star)$ and $s_2(M_\\star)$ without arbitrary colour cuts. This data-driven classifier selects the sample of present-day green valley galaxies; their merger trees in the EAGLE simulation define the main progenitor branches that are followed through the snapshots, and the same $z=0$ boundaries are used to decide when those branches 'enter' or 'cross' the green valley at earlier redshifts.","core_discovery":"The paper's central claim is a three-phase evolutionary narrative for green valley progenitors in the EAGLE simulation. In the early growth phase ($z=10$–$6$), progenitors are gas-rich, efficiently star-forming, mostly low-mass, and reside in low-density environments, with AGN feedback moderating star formation in the more massive systems. In the transition phase ($z=6$–$2$), they migrate toward denser regions, and a rising fraction of interactions and mergers (peaking near $25\\%$ at $z=2$) triggers starbursts that deplete cold gas. In the quenching phase ($z=2$–$0$), AGN activity fades to a few percent and cold gas is progressively depleted; at $z<1$ star formation is suppressed most sharply, and correlations between stellar mass, star formation rate, and cold gas content tighten. The main quantitative result is that the majority of the main progenitor branches of present-day green valley galaxies enter the green valley at redshifts below $z=1$, while roughly $5\\%$ of branches cross the green valley to the red sequence by $z=0.1$ and must later undergo rejuvenation to re-enter it by $z=0$.","pith_inferences":["If the green valley colour locus shifts redward with cosmic time, the published 'entered at $z<1$' fraction is likely an overestimate; a redshift-dependent classification would test this.","The same entropic-thresholding pipeline could be applied to observed colour–mass diagrams at multiple redshifts to see whether the late-entry and rejuvenation signatures appear in real galaxies, not just in EAGLE.","The $\\sim5\\%$ rejuvenation fraction could be sensitive to the mass cut $\\log(M_\\star/M_\\odot) \\ge 8.3$; extending the analysis to lower-mass progenitors may change the apparent bounce rate.","The three-phase picture implies that the green valley is a population-level synthesis of different histories rather than a single transitional state, so treating it as a homogeneous class may obscure underlying diversity."],"forward_implications":["Most of today's green valley population entered the valley only in the last few billion years of cosmic time, making the green valley a predominantly low-redshift phenomenon in EAGLE.","Quenching is not monotonic: the roughly $5\\%$ of main branches that crossed into the red sequence by $z=0.1$ and later returned imply that some galaxies can be temporarily quenched and then reignited.","The dominant quenching driver shifts systematically with redshift, from AGN feedback at $z>6$ through interactions at $z\\approx2$–$6$ to environment and mass at $z<2$, so no single mechanism explains the green valley.","The flattening of the mass–SFR main-sequence slope at $z<1$ indicates that low-mass progenitors quench earlier and faster than high-mass ones, predicting a mass-dependent spread in green valley crossing times."],"supporting_citations":[{"why":"Supplies the EAGLE simulation data from which galaxy properties and merger histories are drawn.","marker":"[88]"},{"why":"Provides the entropic thresholding method that defines the green valley boundaries at $z=0$.","marker":"[85]"},{"why":"Provides the Otsu-based bimodal classification of blue cloud and red sequence on which the green valley segmentation is built.","marker":"[84]"},{"why":"Earlier EAGLE-based study of galaxy colour evolution that this work extends and compares with, including green valley residence times.","marker":"[11]"},{"why":"Sets the AGN luminosity threshold ($L_{\\rm bol} \\ge 10^{43}\\,\\mathrm{erg\\,s^{-1}}$) used to classify AGN activity in progenitors.","marker":"[96]"},{"why":"Defines the interacting-pair criterion (nearest neighbour within 200 kpc with mass ratio 1–10) used to quantify interactions.","marker":"[98]"},{"why":"Provides the $(u-r)$ colour measurements in EAGLE snapshots used for classification.","marker":"[93]"}],"fun_headline_variants":["Green valley galaxies mostly arrive late, some return","Three-phase evolution ends late, with 5% bounce-back","EAGLE: green valley galaxies enter late, 5% return","Late green valley entry, rare rebirth: EAGLE's three phases"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the green valley's colour boundaries, defined at $z=0$, remain valid at higher redshifts, so a branch counted as 'entering' at $z<1$ is genuinely crossing a fixed colour transition rather than just passing through a region that was green only at $z=0$.","fun_headline_variants_meta":{"raw":{"variants":["Green valley galaxies mostly arrive late, some return","Three-phase evolution ends late, with 5% bounce-back","EAGLE: green valley galaxies enter late, 5% return","Late green valley entry, rare rebirth: EAGLE's three phases"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00054,"raw_usage":{"total_tokens":2682,"prompt_tokens":1132,"completion_tokens":1550,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":748,"completion_tokens_details":{"reasoning_tokens":1478}},"tokens_in":748,"tokens_out":1550,"duration_ms":11440,"temperature":1.0,"reasoning_tokens":1478,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T22:33:01.700375+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Recompute the 'entered' and 'crossed' fractions using redshift-dependent green valley boundaries derived from each snapshot's own colour–mass diagram, or from observed colour distributions at $z=1$, $0.5$, and $0.1$; if the majority-entry-at-$z<1$ result or the $\\sim 5\\%$ crossing fraction changes materially, the fixed $z=0$ threshold is responsible.","supporting_citations":[{"cited_title":"al., MNRAS,446, 521 (2015)","cited_arxiv_id":null,"evidence_quote":"Supplies the EAGLE simulation data from which galaxy properties and merger histories are drawn."},{"cited_title":"Pandey, MNRAS,530, 4550 (2024)","cited_arxiv_id":null,"evidence_quote":"Provides the entropic thresholding method that defines the green valley boundaries at $z=0$."},{"cited_title":"Pandey, Astronomy and Computing,44, 100725 (2023)","cited_arxiv_id":null,"evidence_quote":"Provides the Otsu-based bimodal classification of blue cloud and red sequence on which the green valley segmentation is built."},{"cited_title":"et al., MNRAS,494, 5713 (2020)","cited_arxiv_id":null,"evidence_quote":"Sets the AGN luminosity threshold ($L_{\\rm bol} \\ge 10^{43}\\,\\mathrm{erg\\,s^{-1}}$) used to classify AGN activity in progenitors."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Defines the interacting-pair criterion (nearest neighbour within 200 kpc with mass ratio 1–10) used to quantify interactions."},{"cited_title":"al., MNRAS,452, 2879 (2015)","cited_arxiv_id":null,"evidence_quote":"Provides the $(u-r)$ colour measurements in EAGLE snapshots used for classification."}],"review_version":1}