{"id":"c895398b-86f9-4975-b65a-e1ee3b953c8f","arxiv_id":"2608.09086","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Galaxy and subhalo mass fractions relative to dark matter decrease towards the centres of matched cosmic voids, with galaxy-to-subhalo ratios limited by the scarcity of massive subhaloes.","lead":"This paper measures how galaxy, subhalo and dark matter mass are distributed inside matched cosmic voids, using SDSS galaxy data and the ELUCID simulation of the local Universe. It finds that galaxies and massive subhaloes are more strongly depleted than dark matter towards void centres, and that this comparison is most uncertain in the innermost void cores.","discovery_kind":"new_method","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Matched-void equivalence is unvalidated: geometric overlap alone (Sec. 3.2) does not ensure SDSS and ELUCID voids share the same underlying density field, so the central mass-bias trends may compare different environments.","rationale":"The reader's weakest_assumption identifies exactly the load-bearing point: the matched-void framework requires ELUCID to reproduce the same underdense regions as the SDSS galaxy voids. This is the most consequential assumption because if it fails, the paper's main conclusions about environment-dependent multi-tracer mass bias lose their physical meaning. I agree with the reader's identification and with the CONDITIONAL verdict. The paper is carefully written, the methodology is standard, and the authors explicitly discuss coordinate offsets as a source of scatter, but they do not validate that the matched pairs have consistent matter underdensities. The geometric matching criteria in Sec. 3.2 are necessary but not sufficient for establishing physical equivalence. The proposed test—comparing the dark matter density profiles around the two centres within the same ELUCID field—is a direct, data-available check that would settle whether the matched voids indeed share the same density environment. If the profiles agree, the central claim is supported; if they disagree, the observed trends in Rg/dm and Rsub/dm would need re-interpretation. The paper does not warrant rejection because the assumption is plausible given ELUCID's large-scale constraints, but it does warrant the conditional requirement of this validation.","tokens_in":16934,"tokens_out":6208,"duration_ms":66293,"concrete_test":"Using the ELUCID dark matter density field, compute the stacked density contrast profile around the SDSS-defined centres and around the matched ELUCID-defined centres for all 102 pairs, out to r/Rv = 1. If the two stacked profiles differ by more than the quadrature-summed SEM in any radial bin, the matched voids are not tracing the same underdensity and the central mass-bias claim is unsupported; if they agree within errors, the matched-void assumption is validated.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim (Conclusions i–ii) is that Rg/dm and Rsub/dm decrease toward void centres because galaxies and massive subhaloes are increasingly depleted relative to dark matter inside the same matched void environments. This requires that each of the 102 matched SDSS–ELUCID void pairs actually traces the same physical underdensity. The matching procedure (Sec. 3.2) uses only geometric criteria: centre separation d < 0.5 Rmin (Eq. 4) and spherical IoU > 0.4 (Eq. 5). These criteria ensure spatial overlap but do not test whether the two independently identified voids have consistent matter density contrasts. The paper's own Figure 4a shows centre offsets up to 0.5 Rmin, which the authors acknowledge as non-negligible. In the independent-frame measurements (Sec. 4.3), Rg/dm divides galaxy mass measured in the SDSS void by dark matter mass measured in the offset ELUCID void; this is not a local mass ratio unless the two voids are the same. The common-frame scheme (Sec. 4.5) uses the averaged centre, but if the two voids are genuinely different underdensities, the average centre represents neither. The cited consistency of stacked number-density profiles (Zhang et al. 2026) is a population-level statistic and does not validate per-pair equivalence. Without a direct test that matched pairs have identical radial density profiles, the observed decreasing trends could be artifacts of combining different environments.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper presents a matched-void framework combining a volume-limited SDSS DR7 galaxy sample with the ELUCID constrained simulation, producing 102 one-to-one matched void pairs based on geometric criteria (centre separation and spherical IoU). The authors measure three stacked radial mass-ratio profiles: galaxy-to-dark matter (Rg/dm), subhalo-to-dark matter (Rsub/dm), and galaxy-to-subhalo (Rg/sub), and report that the first two decrease toward void centres, indicating that galaxies and massive subhaloes are increasingly depleted relative to dark matter in the deepest underdensities, while Rg/sub is roughly constant outside the innermost core. They attribute the large inner uncertainties in Rg/sub to the scarcity of massive subhaloes (log10(Msub/h^-1 Msun) >= 11.8) rather than to coordinate offsets, and they compare independent-frame and common-frame measurements to separate geometric from statistical effects.","tokens_in":17237,"tokens_out":4719,"duration_ms":51051,"significance":"If the matched-void equivalence is valid, this is a novel and potentially important direct measurement of multi-tracer mass bias in observationally anchored cosmic voids. The paper has clear strengths: it explicitly compares independent-frame and common-frame analyses, provides a diagnostic of the effective sample size as a function of radius, validates the asymptotic multiplicative relation among the three ratios, and honestly states the small-number limitations in void cores. The ELUCID constrained simulation is a well-motivated tool for this purpose, and the paper's methodological framework could be useful for future surveys. However, the central claim relies on an unvalidated assumption that geometrically matched SDSS and ELUCID voids trace the same physical underdensity, and the Rg/sub estimator is defined on a conditionally selected sample; both issues need to be addressed before the conclusions can be fully trusted.","major_comments":[{"comment":"The matching criteria are purely geometric (centre separation d < 0.5 Rmin and spherical IoU > 0.4) and do not establish that each SDSS–ELUCID pair traces the same underlying density field. The central interpretation of Rg/dm and Rsub/dm as ratios within a common environment requires this equivalence. In the independent-frame scheme, Rg/dm divides galaxy mass measured in the SDSS-defined void by dark matter mass measured in the offset ELUCID void; if the two voids are genuinely different underdensities, this is not a local mass ratio. The paper's own Figure 2b shows centre offsets up to the matching limit, and the common-frame average centre may represent neither void. The cited consistency of stacked number-density profiles (Zhang et al. 2026) is a population-level statistic and does not validate per-pair equivalence. I request a direct test: within the ELUCID dark matter field, compare the radial density profile around SDSS void centres with that around the matched ELUCID void centres, or restrict the sample to high-IoU/low-offset pairs and show the trends persist. Without this, the observed decreasing trends could be artifacts of combining different environments.","section":"§3.2, Eqs. (4)–(5); §4.3"},{"comment":"The stacked estimator (Eq. 9) and the SEM (Eq. 10) for Rg/sub are effectively conditional on the presence of a non-zero subhalo mass in the radial shell: voids with M_sub = 0 contribute zero to both numerator and denominator and are excluded. The inner bins are thus computed from a subset of voids that happen to contain at least one massive subhalo (log10(M_sub/h^-1 Msun) >= 11.8). This selection is likely biased toward less empty or more massive environments, and it may explain the approximate constancy of Rg/sub outside the core without invoking a physical insensitivity of the galaxy–subhalo connection. The paper recognizes the decline in effective sample size but does not quantify the selection bias. Please estimate the magnitude of this conditioning effect—for example, by lowering the subhalo mass threshold and recomputing Rg/sub, or by modelling the probability of having a subhalo as a function of radius—before drawing conclusion (ii).","section":"§3.3, Eq. (9); §4.6"},{"comment":"The ELUCID subhalo sample is abundance-matched to the SDSS galaxy sample, and the ELUCID initial conditions are constrained by SDSS galaxy groups. This creates a partial non-independence between the galaxy and subhalo tracer populations: the two are not independent measurements of the same underlying field, and Rg/sub is therefore not a fully independent test of the galaxy–subhalo connection. The paper notes the abundance matching reduces sampling differences, but it does not discuss the circularity concern explicitly. This is especially relevant to conclusion (ii), where a near-constant Rg/sub is interpreted as evidence that the galaxy–subhalo link is insensitive to environment. The authors should state the limitation and, if possible, test robustness by comparing with an unconstrained simulation or a differently constructed subhalo sample.","section":"§2.2; §5.4"}],"minor_comments":[{"comment":"The axis labels in Figure 2 panels (b) and (c) contain garbled text ('Cen20e Distance', 'Numbe0 of V oid P airs', 'M/c/ h'); these should be corrected to standard notation.","section":"§4.2, Figure 2"},{"comment":"The manuscript reports asymptotic values (Rg/dm ≈ 0.0045, Rsub/dm ≈ 0.30, Rg/sub ≈ 0.015) without numerical uncertainties; providing the error bars from the stacked profiles would make the comparison of the independent- and common-frame results more quantitative.","section":"§4.3 and §4.5"},{"comment":"The phrase 'Void Core Statistical Limit Window' appears capitalized in the text and in Figure 6; for consistency with journal style, consider using lowercase or defining it as a formal term upon first use.","section":"§4.6"},{"comment":"The statement 'will be shared on reasonable request' is vague; given the reproducibility emphasis of modern cosmology, please specify what data products (void catalogues, matching code, mass-ratio profiles) will be made available and under what conditions.","section":"Data Availability"},{"comment":"The SEM in Eq. (10) is computed from individual void ratios R_i,j = A_i,j / B_i,j, but the stacked profile in Eq. (9) uses ratio-of-sums; the text explains this distinction, but a reader may wonder which quantity is shown in the figures. Please state explicitly in the figure captions that the plotted points are the stacked ratios and the error bars are the SEM of the individual ratios.","section":"§3.3, Eq. (10)"}],"recommendation":"major_revision","confidential_remarks":"The paper is well structured and the observational anchoring via ELUCID is valuable, but the two major concerns above are load-bearing: the lack of per-pair density-equivalence validation and the conditional selection in Rg/sub. Both are addressable with additional analysis using the existing ELUCID dark matter field, so the work is not beyond repair. The circularity of using SDSS-constrained simulation and abundance-matched subhaloes is a deeper limitation, but it is somewhat inherent to the approach and could be caveated rather than fully resolved. If the authors can provide the requested validation and selection-bias quantification, the paper would be a solid contribution to MNRAS."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Dear colleague,\n\nThis is a genuinely useful paper, and the main result is probably right. The authors construct 102 one-to-one matched void pairs between SDSS DR7 galaxies and the ELUCID constrained simulation, then measure galaxy, subhalo, and dark matter mass ratios as a function of radius. The new thing is the matching itself and the common-frame scheme, which lets them show that coordinate offsets between the two void catalogues inflate the scatter in Rg/dm but not the central trend. They also document, honestly, that the galaxy-to-subhalo ratio in void cores is based on almost nothing: at r/Rv=0.05 only two pairs contribute. That is a real finding about the limits of the method, not a failing.\n\nThe analysis is careful and the claims are hedged appropriately. The central trends—Rg/dm and Rsub/dm fall toward the centre while Rg/sub is roughly flat—survive the switch from independent to common frames, which argues against the worry that the signal is just an artifact of mismatched void centres.\n\nThe soft spots: the matching is purely geometric (centre separation and volumetric overlap), so it does not by itself prove that each SDSS and ELUCID void trace the same underlying matter underdensity. The paper relies on earlier stacked-profile consistency as justification. That is reasonable, but a direct test—e.g., comparing the dark matter density contrast profiles inside each pair—would strengthen the chain. The abundance-matched subhalo sample is thresholded at 10^11.8 Msun/h, so the Rg/sub measurement is conditional on having a massive subhalo in the shell; the authors acknowledge this, but it means the flat Rg/sub profile outside the core is only about voids that contain such subhaloes. Also, no code or catalogue is released, only 'on reasonable request', which limits reproducibility. The ELUCID circularity is real but not fatal: the simulation is constrained by SDSS groups, so the DM field is not fully independent of the observed galaxies, but the comparison is still informative and the paper says so.\n\nOverall: this is a solid, honest contribution that deserves a serious referee and publication. I would ask for the matched-pair density-contrast validation and a public data release, but I would not block on either.","headline":"A careful, honest matched-void analysis whose qualitative trends survive the common-frame check; the main caveat is that matched pairs are only geometrically, not physically, validated.","tokens_in":17753,"tokens_out":3025,"would_cite":true,"duration_ms":32731,"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":"Cosmic voids deplete galaxies and subhaloes toward their centres.","keywords":["cosmic voids","mass bias","multi-tracer","constrained simulation","ELUCID","SDSS","void identification","subhalo scarcity"],"falsifier":"Apply the identical void-matching and stacked mass-ratio pipeline to a mock or unconstrained N-body simulation with known galaxy–subhalo–dark matter assignments; if \\(R_{\\rm g/sub}\\) shows an inward decline while the input galaxy–subhalo relation is constant, the measured trends are artefacts of the matching or stacking procedure rather than properties of cosmic voids.","tokens_in":16746,"feed_emoji":"🕳️","tokens_out":7577,"duration_ms":69110,"temperature":0.7,"pith_summary":"This paper establishes that galaxies and massive subhaloes are progressively depleted relative to the dark matter field toward the centres of cosmic voids, using a sample of 102 void pairs in which each observed SDSS galaxy void is matched one-to-one to a corresponding void in the ELUCID constrained simulation of the local Universe. The key results are the radial mass-ratio profiles: both the galaxy-to-dark matter ratio \\(R_{\\rm g/dm}\\) and the subhalo-to-dark matter ratio \\(R_{\\rm sub/dm}\\) fall steeply inside \\(r/R_{\\rm v} \\lesssim 0.5\\), while the galaxy-to-subhalo ratio \\(R_{\\rm g/sub}\\) stays roughly constant outside the core. A common-frame analysis shows that coordinate offsets between the independently identified void catalogues inflate the scatter in \\(R_{\\rm g/dm}\\) but cannot explain the large uncertainties in \\(R_{\\rm g/sub}\\), which instead trace the scarcity of massive subhaloes in void interiors. The paper's framework matters because it converts the usual statistical comparison of void populations into a direct, environment-by-environment comparison of tracer mass content, and it quantifies the statistical limit that extreme underdensities impose on multi-tracer measurements.","feed_headline":"Mass fractions of galaxies and subhaloes plunge toward void centres","feed_subtitle":"Matched SDSS-ELUCID voids show tracer mass loss deepens at the core, limiting measurements.","key_machinery":"The load-bearing construction is the matched-void catalogue: voids are identified independently in the SDSS real-space galaxy distribution and in the ELUCID subhalo field using the REVOLVER watershed-based void finder within the VAST framework, then paired one-to-one through a proximity criterion (\\(d < 0.5\\min(R_{\\rm SDSS}, R_{\\rm ELUCID})\\)), a sphere-approximated intersection-over-union threshold (\\({\\rm IoU} > 0.4\\)), and mutual best-match selection, yielding 102 pairs. The mass-ratio statistics \\(R_{\\rm g/dm}\\), \\(R_{\\rm sub/dm}\\), and \\(R_{\\rm g/sub}\\) are computed from masses stacked in radial shells, and the multiplicative identity \\(R_{\\rm g/dm} = R_{\\rm g/sub} \\times R_{\\rm sub/dm}\\) validates the measurements in the background regime. A second element is the contrast between an independent-frame scheme, which keeps each catalogue's native centre and radius, and a common-frame scheme, which measures all tracers within the averaged centre \\(C_{\\rm avg}\\) and radius \\(R_{\\rm avg}\\) of each matched pair; this contrast isolates the contribution of coordinate offsets to the observed scatter.","core_discovery":"The paper's central claim is that multi-tracer mass bias inside cosmic voids is environment-dependent and directly measurable in observationally matched systems. Using 102 SDSS–ELUCID void pairs, the stacked mass-ratio profiles show that both the galaxy-to-dark matter ratio \\(R_{\\rm g/dm}\\) and the subhalo-to-dark matter ratio \\(R_{\\rm sub/dm}\\) decline toward void centres, meaning galaxies and massive subhaloes contribute progressively less to the enclosed mass in the deepest underdensities, while the galaxy-to-subhalo ratio \\(R_{\\rm g/sub}\\) stays roughly constant outside the innermost core. The paper attributes the large uncertainties on \\(R_{\\rm g/sub}\\) inside \\(r/R_{\\rm v} \\lesssim 0.5\\) to the scarcity of massive subhaloes (\\(\\log_{10}(M_{\\rm sub}/$h^{{-1}}$M_\\odot) \\ge 11.8\\)): at \\(r/R_{\\rm v}=0.25\\) only 49 of 102 voids contain such a subhalo in the shell, and at \\(r/R_{\\rm v}=0.05\\) only two do. It concludes that coordinate offsets between independently identified void catalogues inflate but do not fully explain the scatter, and that the innermost measurements are limited by small-number statistics.","pith_inferences":["If \\(R_{\\rm g/sub}\\) is genuinely constant across void environments, the galaxy–subhalo mass relation may be universal in underdensities; splitting the sample by stellar mass or colour within the same matched voids could test this.","The same matching and stacking pipeline could be applied to other tracer pairs, such as galaxies versus haloes in unconstrained simulations, to check whether the depletion pattern is specific to subhalo-selected voids.","The quoted small-number-statistics limit suggests that any void-core \\(R_{\\rm g/sub}\\) signal from current surveys is driven by a handful of rare massive subhaloes; stacking by subhalo mass rather than using a fixed threshold might extend the measurable radius inward.","Running the identical pipeline on mock catalogues with known tracer assignments would separate method artefacts from genuine void physics, providing a clean validation not performed in this paper."],"forward_implications":["Because both \\(R_{\\rm g/dm}\\) and \\(R_{\\rm sub/dm}\\) fall toward void centres, voids are not simply low-density copies of the field: the tracer population is progressively biased against the deepest underdensities.","The near-constant \\(R_{\\rm g/sub}\\) outside the core implies that the environmental modulation of \\(R_{\\rm g/dm}\\) is inherited from the subhalo population rather than from a varying galaxy–subhalo connection.","The common-frame scheme reduces the scatter in \\(R_{\\rm g/dm}\\), so future multi-tracer comparisons of void profiles should align coordinate systems before interpreting differences.","Measurements of galaxy-to-subhalo mass ratios inside \\(r/R_{\\rm v} \\lesssim 0.5\\) are statistically unreliable with current survey volumes, since fewer than half the matched voids contribute a massive subhalo at \\(r/R_{\\rm v} = 0.25\\).","Expanded survey volumes that yield more matched void pairs will directly improve the innermost \\(R_{\\rm g/sub}\\) measurement, which the paper identifies as achievable with upcoming datasets such as DESI."],"supporting_citations":[{"why":"Supplies the reconstructed real-space SDSS galaxy catalogue from which observed voids are identified.","marker":"Shi et al. 2016"},{"why":"Describes the ELUCID constrained simulation, providing the dark-matter-only realisation of the local Universe.","marker":"Wang et al. 2014"},{"why":"Presents the ELUCID simulation and its reproduction of observed large-scale structures, the basis for matching voids.","marker":"Wang et al. 2016"},{"why":"Defines the REVOLVER watershed void finder used to identify voids in both catalogues.","marker":"Nadathur et al. 2019"},{"why":"Provides the VAST framework that implements REVOLVER and the interior-void and radius selection criteria.","marker":"Douglass et al. 2023"},{"why":"Shows that REVOLVER yields consistent stacked profiles between SDSS galaxies and ELUCID subhaloes, motivating the void definition choice.","marker":"Zhang et al. 2026"},{"why":"Provides the SDSS galaxy-group constraints that anchor the ELUCID reconstructed density field.","marker":"Yang et al. 2012"},{"why":"Demonstrates ELUCID's large-scale reconstruction fidelity, supporting the assumption that matched voids trace common environments.","marker":"Yang et al. 2018"}],"fun_headline_variants":["Void centres reveal galaxy and subhalo mass loss","Tracer mass ratios plunge inside cosmic void cores","Deep voids deplete galaxy and subhalo mass fractions","Massive subhalo scarcity limits void centre probes","SDSS-ELUCID voids show tracer depletion at cores"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The entire matched-void comparison assumes that the ELUCID constrained simulation, whose large-scale density field is reconstructed from SDSS galaxy groups, reproduces the same physical underdense regions as the galaxy-identified voids, so that each matched pair samples one common void environment rather than two different regions.","fun_headline_variants_meta":{"raw":{"variants":["Void centres reveal galaxy and subhalo mass loss","Tracer mass ratios plunge inside cosmic void cores","Deep voids deplete galaxy and subhalo mass fractions","Massive subhalo scarcity limits void centre probes","SDSS-ELUCID voids show tracer depletion at cores"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000179,"raw_usage":{"total_tokens":1372,"prompt_tokens":1088,"completion_tokens":284,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":704,"completion_tokens_details":{"reasoning_tokens":205}},"tokens_in":704,"tokens_out":284,"duration_ms":3425,"temperature":1.0,"reasoning_tokens":205,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T23:47:19.806387+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Apply the identical void-matching and stacked mass-ratio pipeline to a mock or unconstrained N-body simulation with known galaxy–subhalo–dark matter assignments; if \\(R_{\\rm g/sub}\\) shows an inward decline while the input galaxy–subhalo relation is constant, the measured trends are artefacts of the matching or stacking procedure rather than properties of cosmic voids.","supporting_citations":[],"review_version":1}