{"id":"4e2710d0-9109-48e6-9e4c-00558d73ee4d","arxiv_id":"2502.10078","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Merging galaxies in isolated systems show enhanced star formation at the merger and post-merger stages, while post-starburst post-mergers quench outside-in with AGN playing a minor role.","lead":"This paper studies 137 galaxies in isolated pairs and triplets from the MaNGA survey, sorting them into merger stages and mapping where stars form and where AGN activity appears. It finds that mergers boost star formation, that AGN do not seem to quench it quickly, and that post-merger galaxies with post-starburst features quench from the outside in.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Outside-in quenching claim may be a selection artifact: PSB galaxies are selected via central spaxel, and the Dn4000 gradient lacks galaxy-level significance testing.","rationale":"The reader's conditionality is well placed, but the specific weakest assumption identified was the visual merger-stage classification. My reading points to a more targeted and arguably more load-bearing vulnerability: the PSB outside-in quenching claim is built on galaxies selected by their central spaxel, so the positive Dn4000 gradient might be a selection artifact rather than a physical quenching pattern. This is a concrete, testable concern that does not require disputing the classification scheme. The paper does provide useful independent support—a data catalogue in Appendix D, a public WHAN visualization tool, and p_merger agreement for the six mergers—but none of these addresses the central-spaxel bias. The seven-galaxy sample is too small for the reported mean-profile slope to carry confidence without a galaxy-level bootstrap or aperture-independent PSB selection. These are straightforward additions, so CONDITIONAL remains the correct verdict rather than REJECT; however, if the bootstrap or re-selection removes the positive gradient, the headline claim should be withdrawn. My concern therefore reinforces the reader's conditionality while sharpening the required tests.","tokens_in":39637,"tokens_out":3501,"duration_ms":35652,"concrete_test":"Compute the Dn4000 radial gradient individually for each of the seven PSB galaxies. (1) Bootstrap over the seven galaxies (resample with replacement) and obtain the 95% confidence interval of the mean slope; if the interval includes zero or negative slopes, the outside-in claim fails. (2) Re-select PSB galaxies using an aperture-independent criterion, e.g., requiring PSB spectral features in multiple spaxels across at least two annuli, then recompute the mean radial Dn4000 profile; if the positive slope disappears, the central-spaxel selection is responsible. (3) Compare the CP and PSB radial profiles using stellar-mass-matched subsamples to rule out mass-dependent gradient differences.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim that post-merger PSB galaxies quench outside-in (Sect. 5.2, Fig. 10) rests on the positive mean radial Dn4000 gradient (m = 0.12 ± 0.03) of only seven PSB galaxies. The PSB sample is defined using the central spaxel alone (Sect. 3.1.1): candidates must fall in the PSB region of the WHα vs. (HδA+HγA)/2 diagram at the nucleus. Because a post-starburst population has low Dn4000 while old populations have high Dn4000, this selection directly biases the central Dn4000 downward. The observed positive gradient may therefore be an artifact of conditioning on central post-starburst signatures rather than evidence that quenching propagates from the outskirts inward. Furthermore, the seven PSB galaxies span log M* from 8.7 to 11.1 and include both early- and late-type morphologies; the mean profile mixes heterogeneous galaxies, and the quoted slope uncertainty reflects spaxel scatter, not galaxy-to-galaxy variance. No bootstrap, significance test, or mass-matched control comparison is presented. The paper's strongest statement—'observational proof of the effect of interactions on the quenching process'—is thus not yet supported against this selection effect.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This manuscript classifies 137 galaxies from isolated systems (SIG/SIP/SIT/SIM catalogues) into merger stages: close pairs (CP, 40), pre-mergers (PrM, 21), mergers (M, 6), and post-mergers (PsM, 63), of which 7 are classified as post-starburst (PSB). Using MaNGA integral-field data, the authors perform spaxel-by-spaxel CIGALE spectrophotometric SED fitting, construct spatially resolved WHAN diagrams, and study integrated sSFR, AGN fractions, and radial Dn4000 profiles as functions of merger stage. The main claims are that mergers enhance star formation, that AGN plays only a minor role in post-merger quenching, and that the quenching in post-merger PSB galaxies proceeds outside-in, as inferred from a positive mean radial Dn4000 gradient (m = 0.12 ± 0.03) for the seven PSB galaxies. The paper includes a public visualization tool, detailed CIGALE parameter tables, and a data catalogue, and it compares its visual classification with independent merger indicators (DS18 p_merger and CAS parameters).","tokens_in":39873,"tokens_out":5588,"duration_ms":51581,"significance":"If the outside-in quenching result were robust, it would provide spatially resolved evidence connecting mergers to rapid quenching in low-density environments, a scenario that is plausible and of broad interest. The study uses standard public data, documents the SED-fitting setup, and makes a visualization tool available, which are useful for reproducibility. However, the central gradient result rests on only seven PSB galaxies selected via central-spaxel spectral criteria, and the analysis does not account for the resulting selection bias on Dn4000 or for galaxy-to-galaxy variance. The phrase 'observational proof' in the abstract and conclusions substantially overstates the evidentiary weight of a small, visually classified, descriptive study. The paper's other findings (e.g., enhanced sSFR in the merger/post-merger stages) are consistent with existing literature but would benefit from formal significance testing on galaxy-level samples.","major_comments":[{"comment":"The outside-in quenching claim rests on the positive mean Dn4000 gradient (m = 0.12 ± 0.03) for the seven PSB galaxies. Because PSB selection is made using the central spaxel only (candidates must fall in the PSB region of the WHα vs. (HδA+HγA)/2 diagram at the nucleus), the central Dn4000 is biased low by construction: a post-starburst population has low Dn4000, while older outer regions have high Dn4000. The observed gradient may therefore reflect selection conditioning rather than a quenching front propagating outside-in. In addition, the quoted slope uncertainty comes from the scatter in the mean radial profile, not from galaxy-to-galaxy variance, and the seven PSB galaxies span log M* from 8.7 to 11.1 with both early- and late-type morphologies. I recommend: (1) plotting individual Dn4000 profiles for the seven PSB galaxies; (2) reporting a galaxy-level bootstrap or mixed-effects test of the gradient against zero; (3) constructing a control sample matched in central Dn4000 or PSB strength from non-interacting MaNGA galaxies to demonstrate that the gradient is not a selection artifact; and (4) removing or substantially qualifying the phrase 'observational proof'.","section":"Sect. 3.1.1 and Sect. 5.2 (Fig. 10)"},{"comment":"The manuscript states that 'some galaxies were re-classified or removed' after quality control, with removal when the MaNGA FoV was too small, centered only on the bulge, or lacking good coverage, but it does not report how many galaxies were affected or the exact criteria. Since Table 1 presents only the final counts (CP=40, PrM=21, M=6, PsM=63, PSB=7), the reader cannot assess whether the removals introduce selection bias correlated with the very properties under study. Please provide a full exclusion/reclassification log (galaxy IDs, original and final classifications, reason), and show that the main conclusions are stable under reasonable alternative treatments of the excluded galaxies.","section":"Sect. 5.1"},{"comment":"The claim that 'merger and post-merger stages present higher star formation activity (measured by their integrated sSFR)' is based on descriptive medians for six M and seven PSB galaxies. The interquartile ranges in Table 5 overlap substantially (e.g., CP: −10.85 ± 1.42; M: −9.87 ± 0.53; PsM: −10.09 ± 0.46), and no formal significance test is reported for the galaxy-level distributions. Please add significance tests that treat galaxies (not spaxels) as independent units, state the effective sample sizes, and clarify whether the enhancement survives mass matching or a control-sample comparison. The same applies to the AGN-fraction comparison in Fig. 11, where the M-category percentages are computed from six galaxies.","section":"Sect. 5.3, Figs. 13–15, Table 5"},{"comment":"The phrase 'observational proof of the effect of interactions on the quenching process' overstates what a small, visually classified, single-survey sample can establish. Even if the Dn4000 gradient is robust to the selection effect described above, it is one observable consistent with outside-in quenching, not a proof. Please rephrase to 'consistent with' or 'provides evidence for', and explicitly mention the central-spaxel selection and the small sample sizes as caveats in the conclusions.","section":"Abstract and Sect. 6"}],"minor_comments":[{"comment":"Typographical and grammatical errors should be corrected, including 'shon' -> 'shown', 'di fferent' -> 'different' (appears throughout), and 'W AHN' -> 'WHAN' in Sect. 3.4.","section":"Sect. 5.2"},{"comment":"The text introduces the QA parameter but does not define it explicitly for the SIP case; please provide the definition or a precise reference to Argudo-Fernández et al. (2015) so that the threshold QA < −2 is self-contained.","section":"Sect. 2.2 / Fig. 1"},{"comment":"The main-sequence reference 'Argudo-Fernández et al. 2025, submitted' is used as the grey dashed line in Figs. 13 and 14; since it is not yet public, please add a footnote with the functional form or make the calibration publicly available so that the offset of the sample from the main sequence can be evaluated.","section":"Sect. 5.3"},{"comment":"The linear-fit slopes in the legend are quoted with uncertainties but without significance levels or goodness-of-fit values; please report p-values or confidence intervals for each slope, or state explicitly that the fits are purely descriptive.","section":"Fig. 10"}],"recommendation":"major_revision","confidential_remarks":"The manuscript addresses a timely and interesting question, and the data products and code sharing are commendable. My main reservation is the robustness of the outside-in quenching claim, which I believe is fixable with additional analysis rather than requiring rejection. I would encourage the editor to treat the 'observational proof' phrasing as a required revision point, not a mere stylistic issue."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: this paper has a genuinely new dataset and a plausible story, but its headline claim — outside-in quenching in post-merger PSB galaxies — is vulnerable to a selection effect the authors didn't address. The merger-boost and AGN results are fine as descriptive trends, not much more.\n\nWhat's new: the combination of isolated systems (SIG/SIP/SIT) with MaNGA IFU data and visual staging into CP/PrM/M/PsM, with seven PSB post-mergers. That's a useful sample. The paper is transparent about methods, does CIGALE SED fitting, uses WHAN maps, and shares the visualization code. The comparison of AGN fractions at fixed mass is a nice check.\n\nBut the outside-in claim rests on a slope of 0.12±0.03 from seven galaxies, and the selection is circular: PSB candidates are chosen from the central spaxel, so the central Dn4000 is biased low by construction. The positive gradient is exactly what you'd get from selection, not necessarily from quenching. The authors even note the PSB emission is concentrated in the center. They also call it 'observational proof' — that's overclaiming.\n\nOther soft spots: the merger bin has six galaxies, no formal significance tests for the sSFR differences, and the visual classification has undisclosed removals in Sect. 5.1. The paper acknowledges the removals but doesn't say how many or why beyond 'FoV too small'. That's fixable.\n\nThe paper is not circular in the sense of fitting parameters to itself; SFR and AGN classifications are independent. The comparison with DS18 and CAS parameters is a good sanity check.\n\nMy recommendation: definitely send to peer review, but the authors need to address the selection effect — e.g., compare gradients in a mass-matched sample not selected on central PSB, or at least show the gradient in PSB-selected galaxies versus non-selected controls with similar central Dn4000. They also need to report the removals and add significance tests. The core idea is worth publishing after these revisions.","headline":"The outside-in quenching claim is probably selection-driven, but the isolated merger sample is a useful contribution that deserves a careful revision.","tokens_in":40486,"tokens_out":2599,"would_cite":false,"duration_ms":23911,"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":"Isolated galaxy mergers trigger star formation, show no mass-matched AGN enhancement, and leave post-starburst remnants that quench from the outside in, according to spatially resolved spectra of 137 galaxies.","keywords":["galaxy mergers","isolated galaxies","star formation","active galactic nuclei","post-starburst galaxies","integral field spectroscopy","MaNGA","quenching"],"falsifier":"Measure the radial $D_n(4000)$ gradient and the spatial extent of post-starburst emission in a larger, mass-matched sample of isolated post-merger galaxies with estimated burst ages; if the outside-in quenching claim is correct, younger cores and older outskirts should be present only in post-mergers with interaction signatures, and the gradient should steepen as the burst ages, whereas non-interacting post-starburst galaxies selected by the same emission-line criteria should not show the same signature.","tokens_in":39420,"feed_emoji":"🌌","tokens_out":10104,"duration_ms":86105,"temperature":0.7,"pith_summary":"This paper asks what a galaxy merger actually does to star formation and black-hole activity when the interacting galaxies sit in isolation, where no cluster environment can blur the signature. Using spatially resolved spectra of 137 galaxies divided into close pairs, pre-mergers, mergers, and post-mergers, it finds that the specific star-formation rate jumps at the merger and post-merger stages and that strong-AGN and star-forming regions occupy comparable fractions of the merger-stage spaxels. At fixed stellar mass, close pairs and strongly interacting galaxies show no difference in AGN fraction, which the authors read as evidence that AGN feedback is not the main thing that shuts off star formation after a merger. The paper's central spatial result is that the post-merger galaxies with post-starburst signatures are quenching outside-in, with young stars near the centre and older stars at the edge, a direction that points to the interaction itself rather than to secular aging. If this holds, mergers are not just starburst triggers; they also leave an observable trace in how, and where, galaxies stop forming stars.","feed_headline":"Mergers quench post-merger galaxies from the outside in","feed_subtitle":"Spatially resolved spectra of 137 isolated interacting galaxies show shutdown begins at galaxy edges, not cores.","key_machinery":"The argument rests on a four-stage merger classification — close pairs, pre-mergers, mergers, and post-mergers — anchored by projected separation ($d \\leq 100$ kpc) and a tidal-strength threshold, with post-mergers further split by post-starburst spectral features. The machinery that carries the quantitative claims is spaxel-by-spaxel spectro-photometric SED fitting of MaNGA cubes, which yields star-formation rate and stellar mass surface-density maps, together with spatially resolved WHAN diagrams (an emission-line classification using [N II]/Hα and Hα equivalent width that separates pure star-forming, strong-AGN, weak-AGN, retired, and passive spaxels). The outside-in quenching claim is carried specifically by radial profiles of the $D_n(4000)$ index (a 4000 Å break age indicator, with values below 1.67 marking younger populations): post-merger post-starburst galaxies have positive slopes, meaning younger cores and older outskirts.","core_discovery":"The paper reports that, for 137 galaxies in isolated systems classified into close pairs, pre-mergers, mergers, and post-mergers, integrated specific star formation rate is elevated in the merger and post-merger stages relative to close pairs and pre-mergers; that in the merger stage the fraction of strong-AGN spaxels is comparable to the fraction of pure star-forming spaxels, while close pairs and strongly interacting galaxies of the same stellar mass show no difference in AGN activity; and that the seven post-merger galaxies with post-starburst emission are quenching outside-in, with younger stellar populations in the inner regions and older populations in the outskirts, which the authors present as observational evidence that interactions can set the direction of quenching. The paper also argues that AGN feedback plays a minor role in quenching after a merger and that post-merger transformation proceeds slowly in isolated environments.","pith_inferences":["A testable extension of the outside-in quenching claim is that the radial extent of the post-starburst region should shrink with time since the burst; stacking MaNGA-like IFU data by estimated burst age would show the young-core/old-halo gradient steepening as quenching progresses.","Because the paper's AGN minority conclusion rests on WHAN classifications that can mislabel weak recent star formation as AGN, an independent check with [O III]/Hβ-based BPT or other emission-line ratio maps on the same spaxels would either confirm that the merger-stage AGN fraction is real or reduce it.","The same selection applied to post-starburst galaxies in clusters would isolate whether outside-in quenching is specific to isolated mergers or a general post-starburst phenomenon; cluster harassment might erase the signature.","If isolated post-mergers evolve slowly, then the scatter in quenching stage at fixed stellar mass should be larger in isolated systems than in denser environments, a prediction the current 137-galaxy sample is too small to test."],"forward_implications":["If the merger-stage ordering is a true timeline, the observed rise in integrated sSFR at the merger and post-merger stages means the interaction itself, not the pre-existing galaxy population, drives the star-formation enhancement.","The comparable strong-AGN and pure-star-forming fractions during the merger stage, together with the lack of a mass-matched AGN difference between close pairs and mergers, implies that nuclear activity and star formation are triggered together and that AGN feedback is not the dominant quenching channel after a merger.","Post-merger galaxies without post-starburst emission remain on the star-forming main sequence and appear to be minor-merger products, so only the major-merger branch of the sequence leads to rapid outside-in shutdown.","The positive $D_n(4000)$ radial slope in post-starburst post-mergers, opposite to the inside-out gradients of quenched close pairs, directly ties the direction of quenching to the interaction if the classification is correct.","The placement of post-starburst post-mergers between the main sequence and the quenched region, often with lenticular morphologies, implies that major mergers in isolation can build S0-like remnants and that the transformation takes hundreds of Myr to Gyr in low-density environments."],"supporting_citations":[{"why":"Defines the isolated-galaxy, isolated-pair, and isolated-triplet catalogues and the isolation and member-selection criteria that supply the sample.","marker":"Argudo-Fernández et al. (2015)"},{"why":"Establishes the tidal-strength thresholds used to identify pre-merger and strongly interacting systems in the isolated catalogues.","marker":"Vásquez-Bustos et al. (2023)"},{"why":"Provides the deep-learning morphological types, S0 probabilities, and merger probabilities used to cross-check the visual merger-stage classification.","marker":"Domínguez Sánchez et al. (2018)"},{"why":"Defines the WHAN diagnostic diagram that classifies each spaxel's ionization as pure star-forming, strong or weak AGN, retired, or passive.","marker":"Cid Fernandes et al. (2011)"},{"why":"Supplies the Hα equivalent width versus summed Balmer absorption selection that identifies the seven post-starburst galaxies.","marker":"Zheng et al. (2020)"},{"why":"Earlier spatially resolved post-starburst analysis that frames the interpretation of central versus extended PSB emission and its timescale.","marker":"Chen et al. (2019)"},{"why":"Provides the D_n(4000) = 1.67 threshold and age calibration used to separate young and old spaxels and build the radial quenching profiles.","marker":"Mateus et al. (2006)"},{"why":"Presents the spectro-photometric SED fitting code and the delayed star-formation-history with burst/quench module used to derive SFR and stellar mass maps.","marker":"Boquien et al. (2019)"},{"why":"Supplies the all-MaNGA integrated SFR and stellar mass catalogue used as the reference main sequence and quenched-region contours.","marker":"Sánchez et al. (2016a,b)"}],"fun_headline_variants":["MaNGA: mergers quench post-merger galaxies from outside in","Isolated galaxy mergers leave post-merger galaxies quenching edge-first","Star formation bursts then outside-in shutdown in isolated mergers","137 isolated mergers show post-merger quenching starts at edges","Mergers trigger star formation, then quench galaxies from edges"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The classification of galaxies into close pairs, pre-mergers, mergers, and post-mergers by visual inspection of images is assumed to be accurate and to represent one evolutionary timeline, so that differences between categories can be read as how an individual galaxy evolves through a merger.","fun_headline_variants_meta":{"raw":{"variants":["MaNGA: mergers quench post-merger galaxies from outside in","Isolated galaxy mergers leave post-merger galaxies quenching edge-first","Star formation bursts then outside-in shutdown in isolated mergers","137 isolated mergers show post-merger quenching starts at edges","Mergers trigger star formation, then quench galaxies from edges"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00071,"raw_usage":{"total_tokens":3244,"prompt_tokens":1043,"completion_tokens":2201,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":659,"completion_tokens_details":{"reasoning_tokens":2115}},"tokens_in":659,"tokens_out":2201,"duration_ms":13947,"temperature":1.0,"reasoning_tokens":2115,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T19:29:23.095425+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the radial $D_n(4000)$ gradient and the spatial extent of post-starburst emission in a larger, mass-matched sample of isolated post-merger galaxies with estimated burst ages; if the outside-in quenching claim is correct, younger cores and older outskirts should be present only in post-mergers with interaction signatures, and the gradient should steepen as the burst ages, whereas non-interacting post-starburst galaxies selected by the same emission-line criteria should not show the same signature.","supporting_citations":[{"cited_title":"2006, MNRAS, 370, 721 Méndez-Abreu, J., Debattista, V","cited_arxiv_id":null,"evidence_quote":"Provides the D_n(4000) = 1.67 threshold and age calibration used to separate young and old spaxels and build the radial quenching profiles."}],"review_version":1}