{"id":"00e99b65-1d8d-4faf-a6c0-8cc6d6611fa8","arxiv_id":"2412.08390","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"A 51-source survey finds H2CS and HCS+ abundances track each other almost exactly in massive star-forming regions, indicating a close chemical link.","lead":"This paper reports new millimeter-wave observations of sulfur-bearing molecules H2S, H2CS and HCS+ toward 51 massive star-forming regions, finding that H2CS and HCS+ abundances are tightly correlated. The large homogeneous sample gives astrochemical models a quantitative target for sulfur chemistry in hot cores.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"H2CS–HCS+ correlation may be inflated by common-normalization denominators (H2 and H2S); partial-correlation controls are needed before claiming a specific chemical link.","rationale":"The reader's verdict identifies the model age assumption as the weakest point, and that is a valid concern for the modeling section. However, the central claim of the paper, as reflected in the abstract and conclusions, is the tight abundance correlation between H2CS and HCS+ and the inference of a specific chemical link. The model age is a secondary, explicitly tentative conclusion ('one possible time') and even if it were unsupported, the observational correlation and the hypothesis of chemical linkage would remain. Conversely, if the correlation itself is inflated by a ratio artifact, the main scientific conclusion is substantially weakened. The paper already provides strong supporting evidence that the three molecules trace similar gas (nearly identical line widths, r = 0.98 for H2CS–HCS+ FWHMs). This makes the interpretation plausible, but it does not establish that the abundance correlation is free from denominator-induced covariance. Because the normalization by H2 and by H2S both involve large, source-varying denominators that are correlated with the numerator species, the reported high r values are expected under a null model of independent H2CS and HCS+ abundances. A partial-correlation and null-simulation test, which requires no new data, would settle whether the observed correlation is more than a statistical artifact. Therefore the appropriate verdict remains CONDITIONAL, pending this additional analysis; no change to the reader's verdict is required, but the conditionality should be tied to this specific test rather than only to the model-age critique. This concern is a methodological point, not an attack on the authors' integrity or on the observational dataset itself, which appears valuable and carefully reduced. The test is concrete, cheap, and directly falsifiable.","tokens_in":29497,"tokens_out":6366,"duration_ms":70821,"concrete_test":"Using the beam-averaged column densities in Table B.1, compute log-space partial correlations between N(H2CS) and N(HCS+) controlling separately for log N(H2) and for log N(H2S): r_{H2CS,HCS+|H2} and r_{H2CS,HCS+|H2S}. Then perform a null simulation: independently resample N(H2CS) and N(HCS+) from their observed marginal distributions, divide by the observed N(H2) (and, in a second run, by the observed N(H2S)) for the same sources, and compute the Pearson r for each of 10^4 simulated datasets. If the observed r = 0.94 (H2-normalized) or r = 0.87 (H2S-normalized) falls within the 95% null interval, the correlation does not establish a direct H2CS–HCS+ link beyond the common-normalization artifact. The same test should be repeated for the H2S–H2CS and H2S–HCS+ pairs.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central observational claim—that H2CS and HCS+ are the most tightly correlated S-bearing species—rests on Pearson r = 0.94 for H2-normalized abundances (Fig. 2c) and r = 0.87 for H2S-normalized abundances (Fig. 3). Both normalizations divide two measured quantities by a common denominator: N(H2), derived from C18O, or N(H2S), derived from H2 34S. When a common denominator varies from source to source, it induces a positive correlation between the ratios even if the numerators are statistically independent. This is a standard ratio-correlation artifact. Here the denominator variations are large: N(H2) spans 1.13e22–4.80e23 cm−2 (about 40×), and H2S is itself strongly correlated with both H2CS and HCS+ (r ≈ 0.77 and 0.76 in Fig. 2a,b). Consequently, the reported r = 0.94 may largely reflect the shared H2 denominator rather than a direct chemical link between H2CS and HCS+. The r = 0.87 obtained with H2S normalization is also subject to the same common-denominator effect, because N(H2S) is a large, source-varying quantity. The paper does not report partial correlations, nor does it test against a null model with independent H2CS and HCS+ abundances rescaled by the observed denominators. The similar line widths (Fig. 5, r = 0.98) independently support co-spatiality of the emitting gas, so the interpretation is not baseless, but the strength of the specific correlation claim as evidence for a preferential H2CS–HCS+ chemical connection is overstated without removing the denominator-induced covariance.","agreement_with_reader":"disagree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports IRAM 30-m single-dish observations of H2S 1_10-1_01, H2^34S 1_10-1_01, H2CS 5_14-4_14, HCS+ 4-3, SiO 4-3, HC3N 19-18, and C18O 1-0 toward 51 late-stage massive star-forming regions. Beam-averaged column densities are derived under an assumed LTE excitation temperature of 18.75 K, with H2 column densities from C18O and H2S column densities from H2^34S using a galactocentric 32S/34S relation. The paper reports that the three S-bearing molecules are detected in 50 of 51 sources, that their abundances show strong positive correlations, especially H2CS and HCS+ (Pearson r = 0.94 with H2 normalization and r = 0.87 with H2S normalization, slopes near unity), and that their line widths are similar. A three-phase NAUTILUS chemical model is compared with the observed abundances, and the paper claims a single possible evolutionary time of 2-3e5 yr for most sources. Positive correlations with SiO are interpreted as evidence for shock-related chemistry.","tokens_in":1862,"tokens_out":1989,"duration_ms":56397,"significance":"The survey value of the paper is real: a homogeneous, fairly large sample of hot-core S-bearing species observed with a single telescope and reduced in a uniform manner, with line parameters and column densities made publicly available via Zenodo, is a useful observational contribution. The similar line widths of H2CS and HCS+ (Fig. 5) are an independent and robust indication that the two molecules trace common gas, which is not affected by ratio-correlation artifacts. If the claimed correlation strengths survive appropriate controls, the paper would provide meaningful constraints on sulfur chemistry in massive star-forming regions. However, the headline conclusion that HCS+ and H2CS are the most tightly chemically linked rests on correlation coefficients that may be inflated by common normalization denominators, and the model age claim is a fitted outcome rather than a parameter-free prediction. The central observational and interpretive claims therefore need additional supporting analysis before the paper's conclusions can be accepted at face value.","major_comments":[{"comment":"The headline correlation between H2CS and HCS+ abundances (r = 0.94 for H2-normalized values, r = 0.87 for H2S-normalized values) may be substantially inflated by the common-denominator effect. N(H2) spans 1.13e22 to 4.80e23 cm^-2 across the sample (Table B.1), so dividing two measured column densities by the same source-varying N(H2) induces a positive correlation even if the numerators are independent. The same issue applies, with additional force, to the H2S-normalized comparison, because N(H2S) itself varies by ~2 orders of magnitude and is strongly correlated with both H2CS and HCS+ (r ~ 0.77 and 0.76 in Fig. 2a,b). The paper should report partial correlations, rank-based correlations, or null-model tests in which independent H2CS and HCS+ column densities are rescaled by the observed denominators. The line-width correlation (Fig. 5, r = 0.98) supports co-spatiality, but it does not by itself establish a preferential chemical link between H2CS and HCS+ over H2S; the strength of the chemical-connection claim is overstated without the denominator controls.","section":"§3.3, Figs. 2-3"},{"comment":"The statement that 'there is one possible time (2-3e5 yr) for each source' is a fitted statement, not a model prediction. For each source, the evolutionary time is chosen as the intersection of the observed abundance with the model curve, and the agreement criterion is loose (within one order of magnitude). Figure 7 shows that multiple intersections exist for several molecules and that the selection of filled versus transparent circles is justified only by the assertion that 'the samples are in the same evolutionary stage.' The paper should quantify how many sources have a unique intersection, how many have multiple intersections, and how many are actually reproduced within the stated tolerance for all three molecules simultaneously. As written, the claim of a single 2-3e5 yr epoch for the whole sample is not supported by the presented evidence.","section":"§4.2, Fig. 7"},{"comment":"The absolute abundances used for the model comparison rest on several strong assumptions: a single LTE excitation temperature of 18.75 K for all species, optically thin emission, unity beam filling, and the fixed conversion N(H2) = 4.37e6 N(C18O). The authors acknowledge that the choice of Tex changes the derived H2^34S column density by factors of 1.32, 1.05, and 1.55 for Tex = 37.5, 25, and 10 K, respectively, but H2CS and HCS+ will respond differently to a change in Tex because their partition functions and upper-level energies differ. Since the model-age conclusion depends on matching absolute abundance levels, the paper should propagate a reasonable range of Tex values through all three abundances and show that the claimed 2-3e5 yr intersection survives. Without this, the model comparison is only valid for the specific, unverified Tex assumption.","section":"§2.2, Eq. (2), Table B.1"}],"minor_comments":[{"comment":"The caption for panels (a) and (b) both describe 'the relationship between HCS+ and H2S abundances'; panel (b) should read 'the relationship between H2CS and H2S abundances' to match the plotted quantities.","section":"Fig. 2 caption"},{"comment":"The entry for G031.28+00.06 lists [H2S/HCS+] = 405 ± 2.62, which is inconsistent with the values in Table D.1 (N(H2S)/N(H2) ≈ 5.52e-9 and N(HCS+)/N(H2) ≈ 8.65e-11, giving a ratio of ~64). This appears to be a typographical error and should be corrected.","section":"Table E.1"},{"comment":"The text says H2S, H2^34S, H2CS, HCS+, and HC3N were 'detected in all sources except for G012.90-00.24,' but Table B.1 and Table D.1 list values for G012.90-00.26 and the text later uses G012.90-00.26; please clarify which source is meant and whether the non-detection is in G012.90-00.24 or G012.90-00.26.","section":"§3.1, Tables B.1 and D.1"},{"comment":"The interpretation that slopes close to 1 imply close chemical relatedness should be stated more carefully: a slope of unity in log-log space only establishes a power-law index of one between the two abundance ratios; it does not by itself indicate the same formation route.","section":"§3.3"},{"comment":"The correlations with SiO are modest (r = 0.57-0.68) and the conclusion that 'shock chemistry may be important' is reasonable as a suggestion, but the paper should avoid presenting these moderate correlations as strong evidence without also discussing possible alternative explanations (e.g., common dependence on density or temperature).","section":"§3.3, Fig. 4"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is a useful observational survey and the data release is a plus, but the central 'most correlated' claim needs a partial-correlation or null-model analysis to be convincing, and the model-age claim needs to be reframed as a fit with stated degeneracies rather than a unique prediction. I would support publication after these points are addressed."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Here's the quick take: this is a useful observational paper. New homogeneous IRAM 30-m survey of H2S, H2CS, HCS+ toward 51 late-stage massive star-forming regions, with detections in 50. That roughly triples the sample of comparable studies (Fontani et al. 2023 had 15). They also did careful work on H2S optical depth correction using H234S and the galactocentric 32S/34S relation, and they make line parameters available on Zenodo. That alone is worth having.\n\nThe headline result is the tight correlation between H2CS and HCS+ abundances: r=0.94 normalized by H2, r=0.87 normalized by H2S, with near-unity slopes. The similar line widths (r=0.98 between the two) independently support co-spatial emission, so the chemical-link interpretation is not baseless. But the correlation coefficients as reported should not be taken at face value. Both normalizations involve a common denominator that varies by ~40x (H2) or is itself strongly correlated with the numerators (H2S). That can inflate ratio correlations even when the numerators are independent. The paper does not report partial correlations or a null test. The stress-test note has a fair point here. If the authors want to claim H2CS and HCS+ are preferentially linked, they should show the correlation survives removing the denominator covariance.\n\nThe other soft spot is the chemical-model comparison. Section 4.2 concludes a single age (2-3e5 yr) can reproduce all sources, but that rests on the assumption, stated in the text, that 'the samples are in the same evolutionary stage.' That is asserted, not shown. With a one-order-of-magnitude tolerance and evolutionary time as a free parameter, 'can be reproduced at some time' is a fit, not a prediction. The Tmax=60K case already fails for H2S and they acknowledge the overproduction. This section should be reframed as illustrative rather than a constraint on source ages.\n\nMinor: LTE with a single Tex=18.75K is rough, but they do check with RADEX and quote systematic factors, so that's acceptable for a survey-style paper.\n\nBottom line: the observational dataset is a solid contribution, the correlation claim needs a statistical control, and the modeling claims need a heavy dose of humility. Send it to review; a good referee can help them fix these issues.","headline":"A valuable 51-source survey of sulfur chemistry in hot cores whose headline H2CS–HCS+ correlation should be viewed with a common-denominator grain of salt.","tokens_in":30456,"tokens_out":2273,"would_cite":true,"duration_ms":24209,"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":"In 50 massive star-forming hot cores, the abundances of H2CS and HCS+ track each other almost exactly, with slope 1.00 and r = 0.94.","keywords":["ISM: molecules","ISM: abundances","hot cores","massive star-forming regions","H2CS","HCS+","H2S","shock chemistry"],"falsifier":"Observe H2CS and HCS+ (together with H2S) toward a mixed sample whose evolutionary stages are independently known to differ, such as pre-stellar cores, young and evolved hot cores, and ultra-compact HII regions, and test whether the near-unity slope and $r \\approx 0.94$ correlation survive. If the tight correlation is specific to a narrow evolutionary window, it should weaken or vanish when stages are mixed. Independently, derive ages for the same sources using other molecular clocks and check whether they indeed all lie near $2$–$3\\times10^{5}$ yr; if not, the model-age match is an artifact. A cheaper check is to recompute column densities with excitation temperatures between 10 K and 37 K and see whether the rank correlation and slopes remain close to unity.","tokens_in":29317,"feed_emoji":"🔭","tokens_out":17469,"duration_ms":138471,"temperature":0.7,"pith_summary":"This paper reports single-dish millimetre observations of the S-bearing molecules H2S, H2CS, HCS+, and SiO toward 51 late-stage massive star-forming regions, with detections in 50 sources. The central finding is that the beam-averaged abundances of H2CS and HCS+ are tightly and linearly correlated across the sample, with $r = 0.94$ and slope $1.00$ when normalized by H2; the other pairs (H2S–H2CS, H2S–HCS+) correlate more weakly ($r \\approx 0.76$–$0.77$). The authors read this, together with nearly equal line widths, as evidence that the three molecules are chemically linked, with HCS+ and H2CS sharing the closest connection. They further argue that a three-phase chemical model can reproduce the observed abundances of all three molecules at a single age of $2$–$3\\times10^{5}$ yr for almost every source, and that the increase of S-bearing abundances with SiO indicates an important role for shock chemistry. If the paper is right, H2CS and HCS+ form a tightly coupled abundance pair that can serve as a diagnostic of gas-phase sulfur chemistry in hot cores.","feed_headline":"H2CS and HCS+ abundances track each other 1:1 in 50 hot cores","feed_subtitle":"Near-unity slope and r = 0.94 correlation point to a shared gas-phase sulfur chemistry in massive star-forming regions.","key_machinery":"The load-bearing observational quantity is the across-source Pearson correlation and least-squares slope between beam-averaged abundances, computed with H2S column densities corrected through the H234S isotopologue and the galactocentric 32S/34S ratio relation, H2 column densities from C18O via the standard conversion, and a common LTE excitation temperature of $18.75$ K. The model comparison is carried out with a three-phase chemical code including gas, grain surface, and icy mantle phases, using the paper's stated initial abundances and reaction network, run on a physical model with a $10$ K collapse phase to $n_{\\rm H} = 1.6\\times10^{7}$ cm$^{-3}$ followed by warm-up to 60, 100, or 150 K; the age of $2$–$3\\times10^{5}$ yr is inferred from where the observed abundances intersect the model curves of H2S, H2CS, and HCS+.","core_discovery":"The paper's central claim is that the abundances of H2CS and HCS+ in late-stage hot cores are linearly related with a slope indistinguishable from unity (1.00 when normalized by H2, 1.09 when normalized by H2S) and a Pearson coefficient of 0.94, the tightest of all pairwise relations among H2S, H2CS, and HCS+. The line widths of H234S, H2CS, HCS+, and HC3N are also nearly equal within each source, which the authors take to mean that the transitions trace the same gas. On this basis they conclude that H2S, H2CS, and HCS+ are chemically linked, with HCS+ and H2CS the most correlated pair; they further propose that a three-phase chemical model (gas, grain surface, icy mantle) with a collapse followed by warm-up reproduces the observed abundances of all three molecules at a single time of $2$–$3\\times10^{5}$ yr for almost all sources, and that the increase of S-bearing abundances with SiO indicates an important role for shock chemistry.","pith_inferences":["The near-unity slope of the H2CS–HCS+ relation suggests a shared gas-phase precursor, most plausibly CS reacting with H3+, HCO+, or HCNH+; if so, the correlation should also hold in sources where CS is abundant, and would be worth testing with CS observations in the same fields.","If shock chemistry is genuinely important, sources with stronger shocks (higher SiO) should show enhanced S-bearing abundances even after controlling for line-of-sight column density; the reported correlations with SiO ($r \\approx 0.6$) are moderate, so the causal link remains tentative.","The single-age conclusion may be an artifact of the coarse grid of maximum temperatures (60, 100, 150 K); a model with a continuous temperature ladder would likely spread the inferred ages, and the comparison should be redone.","Extending the same abundance-pair analysis to SO and SO2, which the paper lists as additional S-bearing shock tracers, would test whether the H2CS–HCS+ pair remains tightly correlated when more of the sulfur network is included."],"forward_implications":["H2CS and HCS+ abundances can be used as a paired diagnostic of gas-phase sulfur chemistry in hot cores, with a predicted near-unity slope; sources that deviate from the line would flag unusual physical conditions.","If the single matching age of $2$–$3\\times10^{5}$ yr is real, late-stage hot cores in this sample are observed at a common chemical phase, making S-bearing molecules a clock for massive star formation.","The observed increase of H2S, H2CS, and HCS+ abundances with SiO abundance implies that shock chemistry must be included in models of sulfur-bearing molecules in hot cores, not just thermal warm-up.","The model's overprediction of H2S at a maximum temperature of 60 K indicates missing gas-phase destruction pathways for H2S at lower temperatures, a specific target for future chemical networks.","The approach of correcting H2S through H234S and the galactocentric 32S/34S ratio provides a template for deriving reliable H2S column densities from optically thick lines."],"supporting_citations":[{"why":"Selects the parallax-based sample of massive star-forming regions with 6.7 GHz methanol masers.","marker":"Reid et al. 2014"},{"why":"Updates the parallax measurements used to define the same source sample.","marker":"Reid et al. 2019"},{"why":"Supplies the galactocentric 32S/34S ratio relation used to convert H234S column densities into H2S abundances.","marker":"Yan et al. 2023"},{"why":"Provides the N(H2) = 4.37 × 10^6 N(C18O) conversion underlying all relative abundances.","marker":"Frerking et al. 1982"},{"why":"Provides the three-phase NAUTILUS chemical code used to model H2S, H2CS, and HCS+ abundances as a function of time.","marker":"Ruaud et al. 2016"},{"why":"Supplies the initial elemental abundances adopted in the chemical model.","marker":"Vidal & Wakelam 2018"},{"why":"Provides the chemical reaction network used in the model.","marker":"Vidal et al. 2017"},{"why":"Supplies the comparison sample of S-bearing abundances at different evolutionary stages that extends the trend in the paper's Figure 3.","marker":"Fontani et al. 2023"}],"fun_headline_variants":["H2CS and HCS+ abundances lockstep in hot cores","Hot cores: H2CS-HCS+ 1:1 link, r=0.94","1:1 H2CS-HCS+ correlation points to shared sulfur chemistry","Hot cores: H2CS and HCS+ trace same gas, r=0.94","Sulfur chemistry in hot cores: H2CS and HCS+ tightly correlated"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The claim that a single model age of $2$–$3\\times10^{5}$ yr fits every source assumes that all 50 detected sources are at the same evolutionary stage; if the sources span different stages, picking the 'more reasonable' of several possible age intersections per source is arbitrary and the single-age conclusion is not supported.","fun_headline_variants_meta":{"raw":{"variants":["H2CS and HCS+ abundances lockstep in hot cores","Hot cores: H2CS-HCS+ 1:1 link, r=0.94","1:1 H2CS-HCS+ correlation points to shared sulfur chemistry","Hot cores: H2CS and HCS+ trace same gas, r=0.94","Sulfur chemistry in hot cores: H2CS and HCS+ tightly correlated"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001429,"raw_usage":{"total_tokens":5979,"prompt_tokens":1374,"completion_tokens":4605,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":990,"completion_tokens_details":{"reasoning_tokens":4496}},"tokens_in":990,"tokens_out":4605,"duration_ms":32166,"temperature":1.0,"reasoning_tokens":4496,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T17:51:41.227655+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Observe H2CS and HCS+ (together with H2S) toward a mixed sample whose evolutionary stages are independently known to differ, such as pre-stellar cores, young and evolved hot cores, and ultra-compact HII regions, and test whether the near-unity slope and $r \\approx 0.94$ correlation survive. If the tight correlation is specific to a narrow evolutionary window, it should weaken or vanish when stages are mixed. Independently, derive ages for the same sources using other molecular clocks and check whether they indeed all lie near $2$–$3\\times10^{5}$ yr; if not, the model-age match is an artifact. A cheaper check is to recompute column densities with excitation temperatures between 10 K and 37 K and see whether the rank correlation and slopes remain close to unity.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the chemical reaction network used in the model."},{"cited_title":"J., Pesce, D","cited_arxiv_id":null,"evidence_quote":"Updates the parallax measurements used to define the same source sample."},{"cited_title":"T., Henkel, C., Kobayashi, C., et al.\\ 2023, , 670, A98","cited_arxiv_id":null,"evidence_quote":"Supplies the galactocentric 32S/34S ratio relation used to convert H234S column densities into H2S abundances."},{"cited_title":"A., Langer, W","cited_arxiv_id":null,"evidence_quote":"Provides the N(H2) = 4.37 × 10^6 N(C18O) conversion underlying all relative abundances."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the three-phase NAUTILUS chemical code used to model H2S, H2CS, and HCS+ abundances as a function of time."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the initial elemental abundances adopted in the chemical model."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the comparison sample of S-bearing abundances at different evolutionary stages that extends the trend in the paper's Figure 3."}],"review_version":1}