{"id":"2ed99f7c-eaba-415c-8c6a-43cf3979103e","arxiv_id":"2502.08218","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Interacting galaxies show more disordered, extended HI gas, and smaller companions with more gas disorder have lower gas content and suppressed star formation.","lead":"Astronomers used the FAST telescope's sensitive HI maps to compare eight galaxy pairs with isolated galaxies, finding that interacting galaxies show more disturbed, stretched-out hydrogen gas. The results connect how strongly gas is pulled outside galaxy disks to suppressed star formation in smaller companion galaxies.","discovery_kind":"new_method","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Apollonius-circle HI division is the load-bearing assumption; the secondary-galaxy gas-deficiency headline must be tested against a split-independent M_HI measurement.","rationale":"The paper's most defensible result is the secondary-galaxy trend: it survives Spearman/Kendall tests for several disorder parameters (Appendix F), uses new high-sensitivity FAST data that recover missing flux, and is explicitly separated from the fragile primary-galaxy correlations that the paper itself cautions about. Independent support also comes from the fact that the secondary-galaxy HI-excess correlations are robust to non-parametric tests, which the primary-galaxy correlations are not. However, the chain from raw datacube to M_HI,sec passes through the Apollonius circle, and that step is not tested. The concern is not that the authors are unaware; they state it plainly. The issue is that the headline 'net consequence ... significant decrease' is not shielded from this bookkeeping. A split-independent recomputation is the single check that would decide whether the central claim is physical. Other concerns, such as small sample size, selection of systems with prominent tidal features, the tuned mock rotation curves, and the H2 excess estimated from SFR scaling, are real but secondary; they would lower confidence but do not attack the secondary-galaxy HI result as directly as the flux split.","tokens_in":29993,"tokens_out":6427,"duration_ms":69376,"concrete_test":"Recompute the secondary and primary HI masses after excluding all pixels outside the two HI disks (regions A1∪A2∪A3 in Figure 3) from both galaxy assignments and placing them in a separate intergalactic component, then repeat Table 5 and Table F1. If the secondary Δlog M_HI values are no longer systematically negative and their Spearman anti-correlations with Δ(R12/F123), Δ(F123/Ftot), and Δ(f+12) lose significance (p > 0.05), the Apollonius-circle assignment is creating the headline deficiency. A more decisive version would fit two tilted-ring models plus a bridge component to the datacube and compare the resulting M_HI,sec values directly.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim that tidal interaction significantly decreases the HI and total neutral gas content of secondary galaxies (abstract; Section 6(iii)) depends on assigning each galaxy a HI mass. That assignment is made by a static Apollonius circle (Section 3.1.2, Equations 1-3) on the sky, using only stellar mass ratio and projected separation. The circle does not follow the gas: projection, orbital history, and the physical origin of bridge/tail gas are all ignored, as the authors note in Section 3.1.2. If HI in the bridge or on the primary-side tail originated in the secondary but falls outside the circle, it is counted as primary HI. This bookkeeping can produce exactly the reported pattern: artificially low M_HI for secondaries, artificially high M_HI for primaries, and stronger 'disorder' whenever gas is displaced from disks. The secondary-galaxy correlations in Table 5 and Appendix F, and the abstract's net-decrease statement, would then reflect the flux-division rule rather than the physics of stripping. The authors flag this uncertainty in Sections 3.1.2 and 5.3 but do not quantify its effect on the headline result.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper uses FAST FEASTS single-dish HI observations of eight interacting galaxy systems and ten isolated controls to quantify tidal perturbation of HI morphology. The authors construct control and mock HI disks, define a set of disorder parameters from residual maps (piling, clumpiness, expansion), and correlate these parameters with HI excess, corrected neutral-gas excess, and SFR excess relative to main-sequence relations. They report that interacting systems are more disordered than controls; that HI clumpiness increases with smaller relative velocity; that secondary galaxies show significant anti-correlations between HI/total-gas deficiency and SFR suppression and most disorder parameters; and that primary galaxies show weaker, Pearson-only correlations driven largely by one system (NGC4631). The paper concludes that gas removal dominates the tidal effect on secondaries, while primaries are more complex.","tokens_in":30106,"tokens_out":7228,"duration_ms":73291,"significance":"The significance is moderate. If the secondary-galaxy correlations are physically real, they provide direct evidence from sensitive single-dish HI mapping that tidal interactions strip gas and suppress star formation in less massive galaxies, complementing interferometric studies that miss diffuse flux. The paper's strengths include explicit reporting of Pearson, Spearman and Kendall results in Appendix F, bootstrap uncertainties, and the use of matched controls; the authors also honestly flag the small sample and the uncertainties in HI flux division. However, the headline HI-depletion result depends on a geometric flux-assignment rule, and the primary-galaxy claims are not robust under non-parametric tests.","major_comments":[{"comment":"The Apollonius-circle division is load-bearing for the central claim that secondary galaxies lose HI. The circle assigns all HI inside the projected boundary to the secondary and everything outside to the primary, based only on stellar mass ratio and projected separation; it does not trace gas kinematics or origin. If HI in a bridge or tail originated in the secondary but lies on the primary side of the circle, the secondary M_HI is underestimated, the primary M_HI is overestimated, and the same systems show high disorder. This can create the exact pattern of Table 5 and the abstract's conclusion (iii). The uncertainty is acknowledged in Sections 3.1.2 and 5.3, but no quantitative test is given. I request a sensitivity analysis or an alternative split-independent estimate: for example, re-run the correlations after varying k in Eq. (3) by the stellar-mass uncertainties, reassign bridge/tail flux to the secondary based on the moment-1 velocity field, or use the total-system HI minus a primary-only mask. If the Table 5 secondary correlations survive, the conclusion is secure; if not, the abstract and Section 6(iii) should be softened.","section":"Section 3.1.2 (Eqs 1-3); Section 5.3; Table 5"},{"comment":"The primary-galaxy result as stated in the abstract ('HI and total neutral gas deficiency correlate with more HI piling at two ends') is not supported by non-parametric tests. Appendix F shows no significant Spearman or Kendall correlations for primary ΔlogM_HI or ΔlogM_HI,cor, and Section 5.3 states that the significant Pearson correlations are largely driven by NGC4631; removing it drops the significance to 0.30 and 0.38. Since the abstract and Section 6 present this as a key finding, the manuscript should either move the primary-galaxy statement to a tentative result, report the outlier-removed p-values in the main table, or qualify the conclusion consistently with Appendix F. The authors' own caveat is correct, but the abstract overstates the robustness.","section":"Section 4.2, Table 5, Appendix F, Section 5.3"},{"comment":"The corrected HI excess used for 'total neutral gas' is partly constructed rather than observed. For galaxies without CO images, Δlog M_H2 is obtained from ΔlogSFR via Eq. (10), which assumes the xCOLD GASS scaling relation and quasi-equilibrium. Because SFR excess itself correlates with disorder in secondaries, the ΔlogM_HI,cor correlations in Table 5 can be inflated by construction. The authors flag the quasi-equilibrium caveat in Section 3.3.3, but the abstract still states a decrease in 'total neutral gas content' for secondary galaxies. I ask for a robustness check restricted to the galaxies with direct CO-based H2 measurements, or an explicit statement of how much of the corrected excess comes from Eq. (10).","section":"Section 3.3.3, Eqs (8)-(10)"}],"minor_comments":[{"comment":"The labels 'significance=0.00(0.00)' should define whether this is a p-value or a significance level, and how the two numbers relate to the bootstrap; the current format is ambiguous.","section":"Figure 6"},{"comment":"Table 4 highlights correlations with p<0.10 while Table 5 highlights p<0.05; state this difference in the captions or unify the thresholds.","section":"Table 4 and Table 5"},{"comment":"The phrase 'the correlation significance ... drops to 0.30 and 0.38' should specify that these are p-values (presumably after removing NGC4631) and state the corresponding Pearson coefficients.","section":"Section 5.3"},{"comment":"The statement that 'we remind the readers to be cautious about the inhomogeneity in these parameters' is helpful, but a short table of which inclination values are from which reference, rather than only footnote letters in Table 1, would make the systematics easier to follow.","section":"Section 2.4"},{"comment":"It would help to state explicitly whether the watershed separation of small-galaxy flux is applied before or after the Apollonius division in Section 3.1.2, since both steps affect M_HI.","section":"Appendix B"}],"recommendation":"major_revision","confidential_remarks":"The paper fits MNRAS scope and the FEASTS data are valuable. I agree with the reader's conditional assessment: the secondary-galaxy correlations are the defensible core, but the flux-division dependence must be quantified before the headline gas-depletion claim can be accepted. The primary-galaxy claims need to be downgraded. This is fixable with analysis rather than new data, hence major revision rather than rejection."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Read this if you care about what single-dish HI can say about tidal interactions. The paper introduces a set of disorder parameters (piling, expansion, clumpiness) measured from FAST data that recover diffuse HI missed by interferometers, and it uses controls and mocks to define residual-based morphologies. That part is new and well executed. The correlation between gas deficiency and disorder in secondary galaxies is the real result: it survives Pearson, Spearman, and Kendall tests for several parameters, and it aligns with a simple stripping picture.\n\nWhere it gets shaky: the HI masses for primaries and secondaries come from an Apollonius circle defined by stellar mass ratio and projected separation. The authors flag the caveats themselves, but they never test whether the headline correlations survive a different flux split. If the circle systematically assigns bridge/tail gas to the primary, the secondary deficiency and the primary excess would be partly a bookkeeping effect. That's the first thing I'd want checked. A split-independent measurement, even for a few systems, would settle it.\n\nThe secondary correlations are otherwise reasonably robust. The primary-galaxy story is weaker: the abstract says deficiency correlates with piling at two ends, but those Pearson correlations are driven by one outlier and vanish in Spearman/Kendall. The paper does caution about this in Section 5.3, so it's more an abstract overstatement than a hidden flaw.\n\nSoft spots: sample of eight interacting systems selected for prominent tidal features—so the 'interacting sample has more disorder' comparison is partly selection by construction. The mock rotation curve scaling includes an ad hoc tune to match the data. Neither kills the paper, but both limit how far you can push the quantitative claims.\n\nThe authors are honest and the data release is planned. With a robustness test on the flux division and a qualification of the primary claim, this would be publishable. It deserves a serious referee; I'd send it out.","headline":"Genuinely useful paper on HI disorder in interacting galaxies, but the secondary-galaxy headline depends on an ad hoc flux division that deserves a robustness test.","tokens_in":30721,"tokens_out":2346,"would_cite":false,"duration_ms":25145,"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":"Tidal interaction depletes the neutral gas of the smaller galaxy in a pair and suppresses its star formation, while the larger galaxy's response is weaker and more complex.","keywords":["galaxy interactions","atomic hydrogen (Hi)","star formation suppression","tidal stripping","disorder parameters","FEASTS survey","FAST telescope","galaxy pairs"],"falsifier":"A kinematic decomposition of the Hi in one of the observed pairs — checking whether gas on each side of the division boundary rotates with the assigned galaxy — would test the load-bearing flux split; alternatively, applying the same disorder parameters to hydrodynamical pair simulations with known gas-loss fractions would test whether the correlations recover true stripping.","tokens_in":29701,"feed_emoji":"🔭","tokens_out":13097,"duration_ms":106677,"temperature":0.7,"pith_summary":"Using full-sensitivity atomic hydrogen (Hi) maps from the FEASTS survey, this paper tries to establish what tidal interaction does to the gas reservoirs and star formation of galaxy pairs. The central claim is that the net effect on the smaller (secondary) galaxy is a significant loss of Hi and total neutral gas, together with suppressed star formation, and that these deficits scale with a set of new 'disorder parameters' that quantify how much Hi has been dragged out of the disks. For the larger (primary) galaxies the situation is more complex: gas deficiency tracks the piling of Hi at the two ends of the system, but not its overall expansion or clumpiness. The paper also finds that both members have less Hi inside their disks and more outside than isolated control galaxies. A sympathetic reader would care because this gives a quantitative, morphology-based handle on which stage of an interaction a system is in, and it reconciles conflicting earlier findings on whether interacting galaxies are Hi-rich or Hi-poor.","feed_headline":"The smaller galaxy in a pair loses its gas and quenches star formation","feed_subtitle":"Full-sensitivity HI maps show the smaller galaxy in a pair loses neutral gas; the larger one's fate is more complex.","key_machinery":"The central machinery is a set of newly defined 'disorder parameters' measured from the Hi moment-0 maps and from residual maps obtained by subtracting idealized mock Hi disks. The parameters include the fraction of (residual) Hi flux outside the disks, the fraction piled at the two ends of the system, the expansion parameter $L$ (the geometric extent of Hi normalized by the sum of the disks' radii), and the clumpiness parameter $S$ (the absolute residual sum divided by the moment-0 sum, outside the disks). The comparisons rest on two constructed baselines: control Hi disks made by enlarging and rotating the disks of matched isolated galaxies, and mock disks built with the GALMOD module using an Hi size–mass relation, a universal radial profile, and median rotation curves. A further load-bearing piece is the division of Hi flux between the two galaxies by an Apollonius circle, which assumes the boundary where a test mass experiences equal tidal torque from the two members; the paper itself warns that projection and orbital history make this division uncertain.","core_discovery":"The paper's core discovery is that the net consequence of a tidal interaction on the gas reservoir of the galaxies is a significant decrease in Hi content and total neutral gas content for the secondary galaxies, and that this decrease is statistically tied to the degree of Hi morphological disorder. The disorder parameters — flux fractions outside the Hi disks, residual flux at the two ends of the system, the physical extent of Hi (expansion), and the clumpiness of residual flux — all rise in interacting systems against matched controls. For secondary galaxies, almost all of these parameters anti-correlate with the Hi excess, the corrected (Hi+H2) excess, and the star-formation-rate excess, whereas for primary galaxies only the parameters describing Hi piled at the two ends of the system show significant correlations with gas deficiency. The authors interpret this as gas removal dominating the tidal effect on secondaries, while primaries experience a competition between gas depletion and later accretion from cooling circumgalactic gas, a picture they explicitly label as speculative.","pith_inferences":["Because the disorder parameters are computed purely from the spatial morphology of Hi, they could in principle be applied to interferometric data cubes (with missing-flux corrections) or to simulated galaxy pairs, offering a direct observable-to-simulation bridge; the paper does not make this application.","The paper's two-stage picture for primaries — first depletion as gas is dragged out, then accretion as expanded Hi cools circumgalactic gas — would predict that systems caught just after first passage, with small separation and high disorder, should show the largest Hi deficiency, a test that a larger sample with known orbital phases could check.","If the Apollonius-circle division is biased, the primary/secondary asymmetry itself could be partly an artifact of how bridge and tail gas is assigned; a kinematic decomposition of the Hi using the velocity field would test whether gas near the boundary truly follows the assigned member's rotation."],"forward_implications":["Almost all disorder parameters rise in interacting systems relative to controls, so a single morphology-based measure can flag tidal interaction from an Hi map even when the companion is faint.","Secondary galaxies show a strong and consistent anti-correlation between gas deficiency (Hi and total neutral gas) and Hi disorder: the more disturbed the Hi, the more gas is lost and the more star formation is suppressed.","For primary galaxies, only the piling of Hi at the two ends of the system correlates with gas deficiency, not expansion or clumpiness; the implication is that primary galaxies are not simply stripped, but can later re-accrete gas.","Both members have depressed Hi surface density inside their disks and enhanced density outside, meaning the interaction redistributes gas outward in a systematic, measurable way.","The correlation between clumpiness and relative velocity, and between expansion and stellar-mass ratio, shows that the disorder parameters encode the orbital configuration of the pair."],"supporting_citations":[{"why":"Supplies the FEASTS Hi data cubes and the reduction pipeline that resolve low-column-density gas missed by interferometers.","marker":"Wang et al. 2023"},{"why":"Defines the Apollonius-circle tidal-torque boundary used to split Hi flux between primary and secondary galaxies.","marker":"Elmegreen et al. 1991"},{"why":"Provides the GALMOD tool that builds the idealized mock Hi disks subtracted to make residual maps.","marker":"Di Teodoro & Fraternali 2015"},{"why":"Gives the Hi size–mass relation that sets the radial extent of the mock disks.","marker":"Wang et al. 2016"},{"why":"Supplies the scaling relation used to convert SFR excess into an H2 excess for the corrected neutral-gas excess.","marker":"Saintonge et al. 2017"},{"why":"Defines the Hi fraction main sequence that anchors the definition of Hi excess.","marker":"Janowiecki et al. 2020"},{"why":"Provides the THINGS molecular-gas profiles used as the comparison baseline for primary galaxies' H2 surface densities.","marker":"Leroy et al. 2008"},{"why":"Gives the classical prediction that tidal disruption strength depends on mass ratio and orbital geometry, which motivates the correlation tests.","marker":"Toomre & Toomre 1972"}],"fun_headline_variants":["Tidal interactions strip gas from smaller galaxies and quench star formation","In galaxy pairs, the smaller galaxy loses its gas and quenches","Secondary galaxies in pairs lose gas and stop forming stars","Smaller galaxy in a pair loses gas and quenches star formation; larger's fate complex"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The paper assumes that a single geometric boundary — where a test parcel of gas would feel equal tidal pull from the two galaxies — correctly assigns all the observed gas to one galaxy or the other; if projection effects or gas in bridges between the galaxies bias that split, the measured gas losses and correlations would be systematically wrong.","fun_headline_variants_meta":{"raw":{"variants":["Tidal interactions strip gas from smaller galaxies and quench star formation","In galaxy pairs, the smaller galaxy loses its gas and quenches","Secondary galaxies in pairs lose gas and stop forming stars","Smaller galaxy in a pair loses gas and quenches star formation; larger's fate complex"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000913,"raw_usage":{"total_tokens":3942,"prompt_tokens":985,"completion_tokens":2957,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":601,"completion_tokens_details":{"reasoning_tokens":2878}},"tokens_in":601,"tokens_out":2957,"duration_ms":20237,"temperature":1.0,"reasoning_tokens":2878,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-08T05:58:01.234469+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A kinematic decomposition of the Hi in one of the observed pairs — checking whether gas on each side of the division boundary rotates with the assigned galaxy — would test the load-bearing flux split; alternatively, applying the same disorder parameters to hydrodynamical pair simulations with known gas-loss fractions would test whether the correlations recover true stripping.","supporting_citations":[{"cited_title":"M., Sundin M., Elmegreen B., Sundelius B., 1991, , https://ui.adsabs.harvard.edu/abs/1991A&A...244...52E 244, 52","cited_arxiv_id":null,"evidence_quote":"Defines the Apollonius-circle tidal-torque boundary used to split Hi flux between primary and secondary galaxies."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Defines the Hi fraction main sequence that anchors the definition of Hi excess."}],"review_version":1}