{"id":"c78e8160-94b6-412f-9264-7a2ca7b0bf2c","arxiv_id":"2504.17961","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"In eight early-type galaxies and bulges, no region is dominated by star formation even where molecular gas is abundant, and strong rotational shear likely suppresses star formation.","lead":"This paper maps where stars are and are not forming in eight early-type galaxies and spiral bulges using 100-parsec-scale observations of warm and cold gas. It finds no star-forming regions in these dense stellar systems despite plenty of molecular gas, and points to strong shear from deep gravitational wells as the likely star-formation brake.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The central claim that no SF-dominated regions exist in ETGs/bulges depends on applying kpc-calibrated WHAN boundaries at 100 pc; the paper's own verification against BPT only covers spiral galaxies, not the ETGs where the claim is made.","rationale":"The reader's weakest assumption is the CO-to-H2 conversion factor, which affects depletion-time magnitudes and the inside-out quenching trend. That is a legitimate concern, but it does not bear on the central classification claim (conclusion item i). The more load-bearing assumption for that claim is the validity of WHAN boundaries at 100 pc, which the paper itself flags as novel and verifies only where BPT is reliable. Therefore the reader identified a real but secondary issue; the primary methodological vulnerability is the WHAN calibration transfer. Both concerns are manageable, so the CONDITIONAL verdict stands. The concrete test above would directly probe the classification boundary issue without requiring new observations.","tokens_in":26552,"tokens_out":1590,"duration_ms":18147,"concrete_test":"Regenerate mock 100 pc-resolution SITELLE spectra from photoionisation models of SF regions embedded in old stellar populations with the measured stellar continua of the ETGs, then apply the Cid Fernandes et al. (2011) WHAN boundaries; if genuine SF regions with realistic continuum dilution are classified as retired or LINER, the central claim is weakened and revised boundaries are needed.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The paper's central claim (conclusion item i) is that no SF-dominated region is found in any ETG or bulge, and this rests mostly on the WHAN diagram, because the BPT diagram lacks reliable H-beta and [O III] detections in most ETG spaxels (Section 3.1). The WHAN classification boundaries from Cid Fernandes et al. (2011) were calibrated on kpc-scale SDSS fibre data. The authors acknowledge that applying WHAN at 100 pc is novel and attempt to validate it by comparing with BPT classifications, but the comparison is only meaningful for the three spiral galaxies with reliable BPT detections. In the ETGs and bulges, the BPT data are mostly upper limits (grey points in Figure 2), so the WHAN classification there cannot be cross-checked against an independent SF diagnostic. If the effective W_Halpha threshold separating SF from retired/LINER ionisation shifts at 100 pc resolution -- for example because H-alpha from a genuine embedded SF region is diluted by the strong old-stellar continuum, or because diffuse ionised gas contributes to W_Halpha -- then the conclusion that no SF-dominated region exists could be an artefact of applying kpc-scale boundaries. The paper independently supports the broader quenching picture with depletion-time lower limits and the shear analysis, so the qualitative conclusion is likely robust, but the specific claim 'no SF-dominated region' is directly sensitive to this calibration issue.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper combines SITELLE optical IFU spectroscopy and ALMA CO(2-1)/CO(3-2) mapping for eight early-type galaxies and spiral bulges at ~100 pc resolution, with the aim of measuring resolved star-formation efficiencies and identifying the mechanisms that suppress star formation. Using BPT and WHAN emission-line classifications, the authors report a complete absence of SF-dominated regions in all ETGs and bulges, with ionised gas attributed mainly to old stellar populations and, in the innermost few hundred parsecs, to AGN/LINER activity. They construct sigma_SFR-sigma_mol relations and radial depletion-time profiles, labelling SFRs as upper limits for ETGs and bulges, and compare shear and free-fall timescales in four regularly rotating CO discs to argue that bulge dynamics and shear regulate star formation in at least half the sample. They also discuss AGN feedback, stellar feedback, and galaxy interactions, and close with a call for better SFR tracers and CO-to-H2 conversion factors in ETGs.","tokens_in":26810,"tokens_out":6810,"duration_ms":74193,"significance":"If the central claim holds, this is a valuable observational step: at ~100 pc resolution, gas-rich spheroids show no region where star formation dominates the ionisation, despite abundant molecular gas, strengthening the case that dynamical mechanisms rather than gas depletion quench star formation in these systems. The paper is careful in several respects: the continuum subtraction with pPXF is documented, the ORCS and LUCI extractions are cross-checked, depletion times are consistently reported as lower or upper limits, and the X_CO dependence is acknowledged in Section 4.2.3. The shear analysis is simple but clearly presented, and the data products are made available. The qualitative picture is likely robust, but the strongest specific claim - the complete absence of SF-dominated regions - rests on a novel application of WHAN boundaries that is not independently validated in exactly the objects where the claim is made.","major_comments":[{"comment":"The claim that no SF-dominated region exists in any ETG or bulge, which appears in the abstract and as Conclusion (i), depends almost entirely on the WHAN diagram. As the paper states, the BPT diagram does not provide a robust classification in the ETGs because most spaxels have only upper limits on H-beta and [O III] (the grey points in Fig. 2). The WHAN boundaries of Cid Fernandes et al. (2011) were calibrated on kpc-scale SDSS fibre data, and the validation against BPT in this paper is effective only for the three spiral galaxies, where BPT classifications are reliable. In the ETGs, the strong old-stellar continuum dilutes W_Halpha, and diffuse ionised gas can changes the [N II]/Halpha ratio; a genuine embedded SF region could therefore be classified as 'retired'. Indeed, the authors themselves note that WHAN classifies some spiral-arm regions as Seyfert because of diffuse ionised gas, showing that the diagnostic is sensitive to diffuse emission. This is a load-bearing issue for the central claim. I request either a softened formulation ('no region is classified as SF-dominated under the WHAN classification') with the calibration caveat stated prominently, or additional validation at ~100 pc using an independent SF tracer (e.g., resolved FUV or radio continuum, or a stacking analysis) and a quantitative estimate of how much W_Halpha dilution would be needed to hide a genuine SF region in these old stellar populations.","section":"3.1 (Fig. 2), Conclusions (i)"},{"comment":"The radial depletion-time profiles and the inference of inside-out quenching in Conclusion (iv) are built on Eq. (2) with a fixed X_CO = 2.3e20 cm^-2 (K km/s)^-1 and fixed CO line ratios. Section 4.2.3 acknowledges that spatially resolved studies of nearby galaxies find smaller X_CO in galaxy centres than in discs, and that such a radial dependence 'could therefore (at least partially) explain the observed trend of increasing tau_dep with decreasing galactocentric radius'. This caveat is in tension with the unqualified statement in Conclusion (iv) that the radial profiles 'suggest inside-out quenching'. Please propagate a plausible radial X_CO uncertainty into the tau_dep profiles (e.g., using the range of central-disc contrasts reported by Sandstrom et al. 2013 and Teng et al. 2022) and test whether the inward increase survives, or explicitly present the trend as conditional on a constant X_CO. In addition, the fixed CO(2-1)/(1-0) ratio of 0.8 may be inappropriate for the radio galaxies NGC 383 and NGC 708; the authors note that Ruffa et al. (2019) adopt 2.3 for radio galaxies, and this systematic uncertainty should be quantified for those objects.","section":"4.2.3, Conclusions (iv), Eq. (2)"}],"minor_comments":[{"comment":"For spaxels without a 3-sigma H-beta detection, the extinction correction adopts the H-alpha extinction of the nearest reliable spaxel; a short discussion of the resulting spatially correlated systematic uncertainty on the radial profiles would be helpful.","section":"2.3"},{"comment":"The agreement between WHAN and BPT classifications in the spiral galaxies is described only qualitatively; an overlap fraction or confusion matrix would strengthen the claimed validation of WHAN at 100 pc scales.","section":"3.1"},{"comment":"The radial profiles use annuli of 200 pc width with a step of 100 pc, so adjacent data points are not independent; this should be stated explicitly.","section":"3.3"},{"comment":"The shear-vs-free-fall comparison adopts a fixed scale height H = 100 pc; a sentence on how the tau_shear/tau_ff ratio changes for plausible H values (e.g., 50-200 pc) would make Conclusion (v) easier to assess.","section":"4.1 (Fig. 5)"},{"comment":"There are a few typographical errors, e.g., 'neglegible' in Section 4.1 and 'thethe high-altitude plateau' in the Acknowledgements; please proofread the final version.","section":"Throughout"}],"recommendation":"major_revision","confidential_remarks":"The paper is a solid observational contribution that fits well within the scope of MNRAS. My main concern is that the abstract and Conclusion (i) make a stronger statement than the WHAN calibration currently supports; the authors can address this either by reframing the claim with the appropriate caveat or by providing additional validation at 100 pc scales. The X_CO issue is acknowledged in the text but not propagated into the conclusions, which should be reconciled. I would be willing to see a revised version."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"You should know two things about this WISDOM paper. First, it is one of the first applications of the WHAN diagram at ~100 pc resolution, and it pairs SITELLE optical line maps with ALMA CO maps for eight galaxies. Second, the central claim—that no spaxel in any ETG or bulge is ionisation-dominated by star formation—is probably right as a qualitative statement, but the quantitative edge is softer than the abstract implies, and the authors mostly know it.\n\nWhat is genuinely new: the resolved ionisation classification at this resolution, and the radial depletion time profiles with both lower and upper limits carefully distinguished. The paper also does several things well. The data handling is thorough: pPXF continuum subtraction, cross-checking with two extraction pipelines, and a transparent treatment of upper limits on SFRs in ETGs. They explicitly flag the small sample size, the preselection of low-SFR galaxies, and the fixed X_CO assumption, and they note that a radially decreasing X_CO could erase the rising depletion time trend. That level of honesty is refreshing. The shear analysis for the four regularly rotating discs is a reasonable, well-caveated interpretation rather than an overreach.\n\nThe soft spots are real but not fatal. The WHAN boundaries were calibrated on kpc-scale SDSS fibres; applying them at 100 pc is new, and the validation against BPT only works for the three spiral galaxies where H_beta and [O III] are detected. In the ETGs, BPT mostly gives upper limits, so there is no independent check that the WHAN cut for 'retired' versus 'SF' holds at this resolution. The stress-test note is on target here. Also, the sample is selected to have low SFRs, so finding no SF-dominated regions is partly circular—though the paper does not pretend otherwise. The depletion time lower limits and the shear timescale comparison are independent enough to support the quenching picture, so I would not let the WHAN caveat sink the paper.\n\nMinor: a few figures lack error bars, and the sample of eight is too small for strong statistical claims. But the authors are appropriately careful about that.\n\nWho is this for? Anyone working on quenching, molecular gas in ETGs, or resolved star formation laws. It deserves a serious referee; with moderate revisions to strengthen the ETG-side WHAN validation (or at least explicitly discuss the resolution dependence), it would be a solid MNRAS paper.","headline":"A solid 100 pc-scale study of eight gas-rich ETGs and bulges; the headline 'no SF-dominated regions' is plausible but rests on WHAN boundaries not independently validated in the ETGs themselves.","tokens_in":27429,"tokens_out":1672,"would_cite":true,"duration_ms":20015,"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 eight gas-rich early-type galaxies and bulges, no region within the inner 500 pc is dominated by star-formation ionisation, so Hα traces old stars, not young stars, and star-formation efficiency is suppressed.","keywords":["early-type galaxies","bulges","star formation efficiency","depletion time","BPT diagram","WHAN diagram","molecular gas","shear"],"falsifier":"Find a single spaxel within the inner 500 pc of any of these systems whose line ratios fall in the recombination-line star-formation zone of both the BPT and WHAN diagrams; that would directly refute the paper's central claim. Alternatively, measure the CO-to-H2 conversion factor from dust emission or excitation modelling in ETG centres: if it decreases inward by a factor comparable to the reported depletion-time gradient, the central rise vanishes and the shear-based argument must be re-evaluated.","tokens_in":26340,"feed_emoji":"🔭","tokens_out":7022,"duration_ms":68256,"temperature":0.7,"pith_summary":"The paper combines ~100 pc-resolution maps of warm ionised gas from SITELLE with cold molecular gas maps from ALMA for eight early-type galaxies and spiral bulges. It tries to establish that, despite substantial reservoirs of molecular gas, none of these systems contains a region within the central ~500 pc whose ionisation is dominated by star formation, and that their star-formation efficiencies are suppressed. If correct, this means the usual Hα-based star-formation rates in such galaxies are upper limits, and the quenching mechanism must operate on the efficiency of star formation rather than on the gas supply. The authors further argue that the strong shear produced by the deep, steep potential wells of bulges is an important regulator, at least for half their sample.","feed_headline":"No star-forming regions found inside gas-rich galaxy bulges","feed_subtitle":"Abundant cold gas, yet not one star-forming pocket in their central 500 pc—shear may be the culprit.","key_machinery":"The load-bearing tool is the spatially resolved ionisation classification: the BPT diagram ([O III]/Hβ against [N II]/Hα) and the WHAN diagram (Hα equivalent width against [N II]/Hα, which separates star-forming, Seyfert, LINER, retired and passive regions using only the bright lines). These are combined with CO-to-Hα luminosity ratios, converted to molecular gas surface densities and star-formation-rate upper limits to map the depletion time τ_dep = M_mol/SFR, the inverse of the star-formation efficiency. Tilted-ring fits to the ALMA CO cubes provide rotation curves, from which the shear timescale τ_shear and the free-fall timescale τ_ff are computed and compared.","core_discovery":"Using BPT and WHAN emission-line classifications at ~100 pc resolution, the authors find a complete absence of star-formation-dominated regions in all five early-type galaxies and in the inner 500 pc of the three spiral bulges, even though those regions are rich in molecular gas. The ionised gas is instead classified as 'retired' or LINER-like, i.e. ionised by old stellar populations, with any active-galactic-nucleus ionisation confined to the central ~200 pc. Consequently the Hα-derived star-formation rates for the ETGs are upper limits, and the molecular-gas depletion times are lower limits; most ETGs in the sample show depletion times that rise toward the centre. The tight correlation between molecular gas and Hα surface densities in ETGs, and the comparison of shear and free-fall timescales from CO rotation curves, are used to argue that bulge dynamics—especially strong shear—regulates the star-formation efficiency of at least half the sample.","pith_inferences":["If the CO-to-H2 conversion factor declines toward the centres of ETGs as it does in some disc galaxies, the central rise in depletion time would weaken or vanish; the absence of star-formation-dominated regions would persist, but the case for inside-out quenching would need the X_CO profile to be measured.","The success of the WHAN diagram at 100 pc suggests it could become a workhorse for resolved ionisation studies in quiescent galaxies, since it requires only Hα and [N II], the lines least affected by continuum subtraction.","The shear mechanism predicts a correlation between rotation-curve steepness and depletion time, which could be tested with a larger sample selected by the shape of the central rotation curve.","If Hα is powered mostly by old stars rather than young stars, high-resolution radio or FUV imaging might reveal small, embedded star-forming clumps that produce no detectable H II regions; such a finding would require softening the quenching narrative."],"forward_implications":["No H II region in any of the eight ETGs and bulges within 500 pc meets the star-formation criteria of either the BPT or the WHAN diagram, so Hα in these central regions is not a star-formation tracer.","The lower-limit depletion-time profiles of most ETGs rise toward smaller radii, and the same trend appears in the star-forming regions of the spiral galaxies, pointing to inside-out quenching.","ETGs show a tighter molecular gas–Hα correlation than spiral galaxies, suggesting the ionised gas is tied to the old stellar population rather than to recent star formation.","In the four ETGs with regularly rotating CO discs, the shear timescale is shorter than the free-fall timescale, indicating that shear from the bulge potential is the dominant gas regulator there.","Because AGN and stellar feedback show no clear signs of suppressing star formation in these systems, bulge-potential shear is left as the mechanism most consistent with the observed suppression."],"supporting_citations":[{"why":"Supplies the original BPT emission-line-ratio classification used to separate star formation from other ionisation mechanisms.","marker":"Baldwin et al. 1981"},{"why":"Provides the theoretical boundaries adopted here to classify spaxels as star-forming, Seyfert, LINER or composite in the BPT diagram.","marker":"Kewley et al. 2006"},{"why":"Defines the WHAN diagram and its five categories, which the paper uses to classify regions when Hβ and [O III] are too faint.","marker":"Cid Fernandes et al. 2011"},{"why":"Establishes the kpc-scale Σ_SFR–Σ_mol relation and the molecular-gas depletion time as the key measure of star-formation efficiency.","marker":"Bigiel et al. 2008"},{"why":"Provides the 100 pc-scale Σ_SFR–Σ_mol relation for nearby late-type galaxies against which the ETG and bulge measurements are compared.","marker":"Pessa et al. 2021"},{"why":"Argues that bulge dynamics, especially rising rotation curves, regulates star formation in early-type galaxies; this motivates the shear analysis.","marker":"Davis et al. 2014"},{"why":"Documents the uncertainty of the CO-to-H2 conversion factor and the need for a fixed X_CO to compare molecular gas masses across the sample.","marker":"Bolatto et al. 2013"},{"why":"Presents a prior 100 pc-scale analysis of one galaxy in the sample, linking the depletion-time profile to bulge simulations and justifying the methods used here.","marker":"Lu et al. 2022"}],"fun_headline_variants":["Gas-rich bulges show no star-forming pockets","Shear stifles star formation in galaxy bulges","Empty star-forming regions in gas-rich bulges","No star formation in bulges despite abundant gas"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The molecular gas masses, and hence the depletion-time profiles and the inside-out quenching conclusion, assume a single CO-to-H2 conversion factor and fixed CO line ratios; if the conversion factor is lower in the centres of early-type galaxies and bulges, the central rise in depletion time would weaken or disappear.","fun_headline_variants_meta":{"raw":{"variants":["Gas-rich bulges show no star-forming pockets","Shear stifles star formation in galaxy bulges","Empty star-forming regions in gas-rich bulges","No star formation in bulges despite abundant gas"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000173,"raw_usage":{"total_tokens":1339,"prompt_tokens":1069,"completion_tokens":270,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":685,"completion_tokens_details":{"reasoning_tokens":210}},"tokens_in":685,"tokens_out":270,"duration_ms":3309,"temperature":1.0,"reasoning_tokens":210,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-16T10:28:03.208401+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Find a single spaxel within the inner 500 pc of any of these systems whose line ratios fall in the recombination-line star-formation zone of both the BPT and WHAN diagrams; that would directly refute the paper's central claim. Alternatively, measure the CO-to-H2 conversion factor from dust emission or excitation modelling in ETG centres: if it decreases inward by a factor comparable to the reported depletion-time gradient, the central rise vanishes and the shear-based argument must be re-evaluated.","supporting_citations":[],"review_version":1}