{"id":"5fe46a57-32d4-4bcd-b9c7-8a8c3d56363e","arxiv_id":"2505.15060","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Multi-phase gas observations in A2626 show HI is more extended and stripped than CO, yet molecular gas also shows asymmetries and deficiencies, indicating environment affects both gas phases in a relaxed cool-core cluster.","lead":"This paper maps the cold gas in ten galaxies of the A2626 galaxy cluster, using ALMA and SMA to trace molecular gas (CO) and MeerKAT to trace atomic hydrogen (HI). It finds that atomic gas is stripped more easily, but molecular gas can also be disrupted, so star-forming fuel in cluster galaxies is affected in both phases.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Excluding CO non-detections without upper limits leaves the claimed H2-deficiency contrast with Virgo in A2626 unsubstantiated.","rationale":"The morphological result (HI more extended, some CO asymmetries and disturbed kinematics) is well illustrated and likely robust, so I do not dispute that part. The novel quantitative claims, however, hinge on the 10 detected CO galaxies being representative. The paper itself notes sensitivity limitations (Sec. 3.4) but neither lists upper limits nor tests whether the detected subset differs from the full 44-galaxy candidate pool. The direction of the bias is subtle: if non-detections are H2-poor, the observed H2 deficiency is an underestimate, which would strengthen the 'H2 def > HI def' offset but could weaken the 'A2626 less deficient than Virgo' conclusion. Moreover, Table 5 lists H2 deficiencies without uncertainties; the M_H2 errors and the xCOLDGASS scatter (~0.3 dex) are comparable to the reported median offset, so the central 'low HI but high H2 deficiency' pattern may not be statistically significant. The reader's conditional verdict already captures this, and the remedy—adding upper limits and error bars—is feasible with existing data. I therefore keep the verdict unchanged.","tokens_in":19989,"tokens_out":14277,"duration_ms":124305,"concrete_test":"Compute 3-5 sigma CO(2-1) integrated flux upper limits for the 10 non-detected ALMA/SMA targets using the reported RMS and a line-width assumption (e.g., from the HI profile), convert to M_H2 upper limits with the same alpha_CO=4.3 and r21=0.79, and re-derive the H2 deficiency distribution using survival analysis (e.g., Kaplan-Meier estimator or censored likelihood). Compare the resulting median H2 deficiency for A2626 and the H2-minus-HI deficiency offset with the Virgo values from Zabel et al. (2022), including bootstrap uncertainties. If the A2626 median with upper limits remains below Virgo by more than 1 sigma, the cool-core/less-stripping narrative holds; if it overlaps or exceeds Virgo, the central quantitative claim fails.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The most load-bearing assumption is that the 10 CO-detected galaxies are representative enough to support the quantitative claims (low HI but high H2 deficiency, higher gas fractions, shorter depletion times than Virgo). Only 9/17 ALMA and 4/6 SMA targets were detected; the 10 non-detections are silently dropped from the deficiency, gas-fraction, and depletion-time analyses, and no CO(2-1) upper limits are given (Sec. 3.4). If the non-detections are preferentially H2-poor, the detected sample is biased toward H2-rich galaxies. For the comparison with Virgo, this matters: the claim that A2626 galaxies are less H2-deficient than Virgo (Sec. 4) could reverse if upper limits push the A2626 median up toward Virgo's. Conversely, the 'H2 deficiency > HI deficiency' offset would be understated, so that sub-claim's direction is robust. The deeper problem is that deficiency values in Table 5 carry no uncertainties: H2 mass errors and the scatter in the xCOLDGASS expected masses are ~0.2-0.5 dex, comparable to the median offset between H2 and HI deficiency (~0.14 dex). Without error bars or significance tests, the headline quantitative conclusion is not established.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper presents ALMA and SMA CO(2-1) observations of 10 galaxies in the A2626 cluster, combined with MeerKAT H I data, to study environmental effects on atomic and molecular gas. The authors compare H I and CO morphology and kinematics, compute H I and H2 deficiencies relative to xGASS/xCOLDGASS scaling relations, and compare gas fractions and depletion times with Virgo and GASP samples. They conclude that H I is more extended and more easily stripped, but CO also shows asymmetries and H2 deficiencies; A2626 galaxies have lower H I deficiencies but higher H2 deficiencies than Virgo, higher gas fractions, and shorter depletion times (0.3-3 Gyr), implying enhanced star formation efficiency, with no correlation between H2 deficiency and cluster-centric distance or velocity.","tokens_in":20209,"tokens_out":6966,"duration_ms":53758,"significance":"If the quantitative conclusions survive scrutiny, the paper would provide a notable counterpoint to the usual picture that H I is affected before H2: in the relaxed cool-core cluster A2626, the molecular phase may be relatively more depleted than the atomic phase. The dataset is valuable—spatially resolved CO and H I for 10 galaxies, with a careful ALMA/SMA consistency check confirming that ALMA does not resolve out significant flux. The morphological/kinematic evidence (Figures 6 and 7) is credible and supports the qualitative claim that H I is more extended and that some CO discs are asymmetric. However, the current analysis does not establish the quantitative claims because the CO-detected sample is a biased subset, and the deficiency and depletion-time comparisons lack error bars and significance tests.","major_comments":[{"comment":"The quantitative comparison of H2 deficiency with Virgo rests on the 10 CO-detected galaxies, while 8 of 17 ALMA targets and 2 of 6 SMA targets were not detected and are silently excluded from the deficiency, gas-fraction, and depletion-time analyses. If the non-detections are preferentially H2-poor, the median H2 deficiency of A2626 would shift toward the Virgo values and could erase the claimed contrast. The text notes 'sensitivity limitations' as a possible cause, but no CO(2-1) upper limits are given. Please add flux or mass upper limits for the non-detections (using the RMS and an assumed line width) and recompute the deficiency distributions including these limits, or explicitly justify their exclusion.","section":"Section 3.4, Table 5, Fig. 8"},{"comment":"The central quantitative result—that H2 deficiency exceeds H I deficiency in A2626—is presented without uncertainties on the deficiency values. From Table 5, the H2 mass errors range from ~0.05 to ~1.0 dex, and the xCOLDGASS expected-mass relation has intrinsic scatter of ~0.2–0.5 dex, comparable to or larger than the median offset between H2 and H I deficiency (~0.14 dex). Without propagating these errors and performing a significance test (e.g., bootstrap or a paired test), the headline offset is not established. Please report deficiency uncertainties and a statistical assessment of the offset.","section":"Eq. (2), Table 5, Fig. 8"},{"comment":"Section 3.1 refers to 'Figure 2' as presenting the CO(2-1) moment 0 and moment 1 maps and global spectra for the ALMA-detected galaxies, but Figures 2–4 in the manuscript are captioned as H I moment maps and profiles. The CO maps are not displayed anywhere, so the reader cannot verify the individual morphological and kinematic descriptions (e.g., 'elongated and asymmetric' for H I ID 15, 'clumpy and extended' for H I ID 107). Please either include the CO maps as a figure or renumber the reference so the evidence is available.","section":"Section 3.1, Figs. 2–4"},{"comment":"The claim that A2626 galaxies have shorter depletion times (median ~1.2 Gyr) than VERTICO galaxies (~3–5 Gyr) is made without uncertainties on the depletion times or SFRs, and it inherits the selection bias of the CO-detected sample. The WISE 12-um SFRs have quoted errors of ~0.3–1.5 M_sun/yr (Table 3), which propagate into the depletion time. Please provide error bars or a sensitivity test, and state how the CO non-detections would affect the median.","section":"Section 3.6, Fig. 11"}],"minor_comments":[{"comment":"The phrase 'moderately enhanced star formation efficiency A2626 galaxies' is missing a preposition ('in').","section":"Abstract"},{"comment":"The caveat that the SMA detection may have captured only part of the CO reservoir should be reflected in the H2 mass uncertainty for H I ID 170 in Table 5, which is reported with an uncertainty of 0.352 dex.","section":"Section 3.1, H I ID 170"},{"comment":"The H I class column uses Arabic numbers (0, 1, 2) while the text refers to classes I–V; please clarify the mapping so the absence of class III and IV is unambiguous.","section":"Table 3, column (11)"},{"comment":"The equation normalizes r21 by 0.7, but the text adopts r21 = 0.79; please state explicitly that the scaling uses the adopted value relative to 0.7, or update the normalization to 0.79 to avoid confusion.","section":"Eq. (1)"},{"comment":"The caption states that 'all but one' CO profiles are from ALMA, but the text excludes H I ID 8 from Figure 7; please clarify the exact number of profiles shown and which galaxies are included.","section":"Figure 7"},{"comment":"The sample selection is described as requiring the expected CO disc to span at least three beams; this criterion favors galaxies with larger optical radii and should be listed among the selection effects affecting the deficiency comparison.","section":"Section 2"},{"comment":"Healy et al. (2021a,b) are cited as arXiv e-prints; please provide the published versions if available.","section":"References"},{"comment":"'My acknowledgments:' appears to be a leftover template phrase; please remove.","section":"Acknowledgments"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is a draft (dated May 22, 2025) with several presentation issues, including a mislabeled figure reference and template artifacts. The underlying dataset is valuable, and the morphological/kinematic comparisons are credible. The main risk is that the quantitative deficiency and depletion-time claims are not yet supported by the analysis as presented. I recommend major revision rather than rejection, as the core evidence can be strengthened by adding upper limits, error propagation, and significance tests within the manuscript's scope."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The genuinely new thing here is the data: first spatially resolved CO(2-1) mapping of A2626, combined with the existing MeerKAT HI. The ALMA/SMA cross-check for three galaxies, showing no missing flux, is careful and credible. The visual morphology (HI extended and asymmetric, CO more central, some CO discs lopsided) is convincing and useful. That alone makes the paper worth reading for cluster ISM people.\n\nThe soft spots are in Sections 3.4-3.6. The deficiency values in Table 5 carry no error bars, and the expected-mass scatter from xCOLDGASS is ~0.2-0.5 dex, comparable to the claimed HI-vs-H2 deficiency offset (~0.14 dex). The ten non-detections are silently excluded from the deficiency, gas-fraction, and depletion-time analyses. If those missing galaxies are H2-poor, the detected sample is biased H2-rich, which would push A2626's H2 deficiencies up. The direction of the 'H2 more deficient than HI' offset may actually be understated, but the comparison with Virgo could weaken or reverse. The sample was also pre-selected to have CO discs spanning at least three beams, another selection effect not discussed.\n\nThere is also a stray 'My acknowledgments:' in the acknowledgments, and HI ID 8's HI detection lies outside the MeerKAT primary beam (flagged in the text but still used in the deficiency sample). No significance testing appears anywhere; the phase-space non-correlation rests on ten points.\n\nFor a paper with genuinely new data, I would send it to review, but ask for major revision: include upper limits for non-detections, propagate uncertainties into the deficiency values, show significance tests, and discuss selection biases. The morphological core is fine; the quantitative claims need to be reined in or properly supported.","headline":"First CO map of A2626 is a useful data release, but the claimed H2-vs-HI deficiency contrast rests on a biased, error-bar-free sample.","tokens_in":20856,"tokens_out":3100,"would_cite":true,"duration_ms":27998,"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":"In the A2626 cluster, the molecular gas is depleted even though the atomic gas survives, suggesting the cluster's calm core shapes how gas is removed.","keywords":["galaxy clusters","molecular gas","atomic hydrogen","ram pressure stripping","CO(2-1) observations","star formation efficiency","cool-core cluster","A2626"],"falsifier":"Deep CO(2-1) observations of the ALMA and SMA targets that were not detected would settle the point: if most of those galaxies turn out to have very low H2 masses, the apparent 'HI-normal but H2-poor' pattern may be an artifact of excluding faint CO emitters. A second test would compare A2626 with a matched-mass non-cool-core cluster using the same deficiency definition; if H2 deficiencies turn out similar, the cool-core explanation rather than sample selection would need revision.","tokens_in":19754,"feed_emoji":"🌌","tokens_out":6282,"duration_ms":53945,"temperature":0.7,"pith_summary":"This paper uses matched CO(2-1) and HI observations of ten galaxies in the A2626 cluster to test which cold-gas phase is removed first in a dense environment. It argues that in A2626, a relaxed cool-core cluster, the atomic gas is more extended and shows stripping signatures, yet the galaxies are only mildly HI-deficient; instead they are comparatively more H2-deficient, with higher gas fractions and shorter depletion timescales (0.3-3 Gyr) than Virgo galaxies. The implied picture is that cluster dynamical state matters: A2626's calm intracluster medium weakens ram-pressure stripping of atomic gas, while local interactions or early infall still erode the molecular phase. If correct, the paper shows that molecular gas depletion is not reserved for violent clusters and that the standard 'HI is stripped first' sequence is environment-dependent.","feed_headline":"Calm cluster depletes molecular gas while neutral gas survives","feed_subtitle":"ALMA and MeerKAT maps of A2626 show low HI but high H2 deficiencies and short depletion times.","key_machinery":"The argument is carried by a joint morphological and kinematic comparison of the two gas phases, using CO(2-1) cubes from ALMA and SMA and HI cubes from MeerKAT, overlaid on optical images. Gas content is quantified with the deficiency definition $\\mathrm{def}_i = \\log M_{i,\\mathrm{exp}} - \\log M_{i,\\mathrm{obs}}$ from Zabel et al. (2022), where expected masses come from stellar-mass-matched field samples, and the paper compares these deficiencies, total gas fractions, and depletion times ($M_{\\mathrm{HI}}+M_{\\mathrm{H2}}$ over SFR) against Virgo and GASP samples while placing the galaxies on a projected phase-space diagram ($R/R_{200}$ versus $\\Delta v/\\sigma_{\\mathrm{cl}}$). The mechanism that carries the interpretation is the contrast between A2626's relaxed cool-core intracluster medium and Virgo's unrelaxed non-cool-core state.","core_discovery":"On the paper's own terms, the central discovery is that environment can deplete molecular gas while leaving atomic gas relatively intact. In the ten detected A2626 galaxies, HI is morphologically extended and often asymmetric or truncated, while CO is centrally concentrated; nevertheless, the sample shows low HI deficiencies but elevated H2 deficiencies relative to expected masses from field scaling relations, and several galaxies have lopsided CO distributions or disturbed velocity fields. The authors interpret this as the signature of a cool-core cluster: weaker ram-pressure stripping allows galaxies to keep their HI, while earlier infall or local galaxy-galaxy interactions act on the molecular reservoir. A2626 galaxies also sit at higher gas fractions and shorter depletion timescales than Virgo galaxies, implying moderately enhanced star formation efficiency, and the paper finds no correlation between H2 deficiency and cluster-centric radius or velocity, which it reads as evidence that current cluster location is not the main driver of molecular gas loss.","pith_inferences":["If this pattern holds, cluster dynamical state should become a standard axis in environmental-quenching models, not just cluster mass and radius.","A direct extension would be to measure the same HI and H2 deficiency pair in a sample of cool-core versus non-cool-core clusters matched in mass and redshift; the paper's logic predicts a systematic offset in the HI-versus-H2 deficiency plane.","The short depletion times suggest that pre-processing or tidal compression may convert or consume molecular gas before ram-pressure stripping removes atomic gas; this could be tested by checking whether the H2-deficient galaxies have enhanced central stellar surface densities or compact bulges.","Upper limits on CO for the non-detected galaxies would let the deficiency statistics be recomputed with a survival analysis, testing whether the reported pattern survives selection effects."],"forward_implications":["A2626 galaxies show low HI deficiencies but elevated H2 deficiencies, opposite to the usual expectation that atomic gas is depleted first.","Several galaxies have asymmetric or truncated CO discs and disturbed velocity fields, so molecular gas is not fully shielded in dense environments.","Depletion times of 0.3-3 Gyr imply moderately enhanced star formation efficiency relative to Virgo galaxies.","The absence of a correlation between H2 deficiency and cluster-centric radius or velocity favors early infall or local interactions over current cluster position as the driver.","Cluster dynamical state (relaxed cool-core versus unrelaxed non-cool-core) is a plausible control on how environmental gas removal proceeds."],"supporting_citations":[{"why":"Supplies the stellar-mass-based deficiency definition used for both HI and H2 and the Virgo comparison sample.","marker":"Zabel et al. 2022"},{"why":"Provides the VERTICO Virgo molecular-gas survey that anchors the H2 deficiency and depletion-time comparisons.","marker":"Brown et al. 2021"},{"why":"Provides the GASP comparison sample for HI and H2 deficiencies and gas fractions in stripping galaxies.","marker":"Moretti et al. 2023"},{"why":"Establishes the Virgo HI deficiency baseline against which A2626's low HI deficiencies are contrasted.","marker":"Chung et al. 2009"},{"why":"Supplies the HI morphological classification scheme used to categorize the A2626 galaxies.","marker":"Yoon et al. 2017"},{"why":"Provides the MeerKAT HI survey of A2626 from which the sample, HI masses, and HI morphologies are drawn.","marker":"Healy et al. 2021a"},{"why":"Supplies the adopted CO-to-H2 conversion factor alpha10 = 4.3 used to compute molecular gas masses.","marker":"Bolatto et al. 2013"},{"why":"Provides the xCOLDGASS field gas-fraction trend that anchors the deficiency and total-gas-fraction comparisons.","marker":"Saintonge et al. 2017"},{"why":"Supplies the equation converting integrated CO(2-1) flux and luminosity distance into H2 mass.","marker":"Watson & Koda 2017"},{"why":"Supports the baseline expectation that molecular gas is more gravitationally bound and resistant to stripping, which the paper nuances.","marker":"Bacchini et al. 2023"}],"fun_headline_variants":["Cool-core cluster depletes molecular gas, spares atomic gas","A2626: molecular gas deficient, atomic gas intact","Weak ram pressure in A2626 allows HI retention, not H2","Galaxies in calm cluster lose H2 but keep HI"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The comparison of HI and H2 deficiencies assumes that the ten galaxies detected in CO are representative of A2626's galaxy population; the eight observed but non-detected galaxies are left out of the deficiency, gas-fraction, and star-formation-efficiency analyses, and if those galaxies are preferentially H2-poor the claimed pattern would be biased.","fun_headline_variants_meta":{"raw":{"variants":["Cool-core cluster depletes molecular gas, spares atomic gas","A2626: molecular gas deficient, atomic gas intact","Weak ram pressure in A2626 allows HI retention, not H2","Galaxies in calm cluster lose H2 but keep HI"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000275,"raw_usage":{"total_tokens":1683,"prompt_tokens":1028,"completion_tokens":655,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":644,"completion_tokens_details":{"reasoning_tokens":583}},"tokens_in":644,"tokens_out":655,"duration_ms":6435,"temperature":1.0,"reasoning_tokens":583,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T15:24:31.330412+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Deep CO(2-1) observations of the ALMA and SMA targets that were not detected would settle the point: if most of those galaxies turn out to have very low H2 masses, the apparent 'HI-normal but H2-poor' pattern may be an artifact of excluding faint CO emitters. A second test would compare A2626 with a matched-mass non-cool-core cluster using the same deficiency definition; if H2 deficiencies turn out similar, the cool-core explanation rather than sample selection would need revision.","supporting_citations":[{"cited_title":"C., & Koda, J","cited_arxiv_id":null,"evidence_quote":"Supplies the equation converting integrated CO(2-1) flux and luminosity distance into H2 mass."},{"cited_title":"M., et al","cited_arxiv_id":null,"evidence_quote":"Supports the baseline expectation that molecular gas is more gravitationally bound and resistant to stripping, which the paper nuances."}],"review_version":1}