{"id":"f549c9cb-d853-4089-929b-88e515dd205f","arxiv_id":"2508.16234","paper_version":1,"verdict":"UNVERDICTED","confidence":"LOW","novelty_score":6.0,"correctness_risk":"unknown","formal_verification":"none","parameter_count":3,"one_line_summary":"Simulations find the FAST Core Array interferometer can detect HI galaxies to z~1 with enough number density for power spectrum and BAO constraints, while single-dish surveys are shot-noise limited beyond z~0.35.","lead":"This paper uses simulations to compare two ways of running a future hydrogen-galaxy survey with the FAST radio telescope: the single-dish mode and a proposed 'Core Array' of dishes working together as an interferometer. It finds the array could detect hydrogen galaxies far enough away (redshift ~1) to constrain dark energy, while the single dish works only at shorter distances.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Quantitative z~1/BAO claim rests on unstated instrument and HI-mass-function inputs; the readable text does not validate them, so the central claim is conditional.","rationale":"The reader's weakest-assumption analysis identifies exactly the load-bearing condition: the z~1 detection and 'sufficient number density' claims depend on unstated simulated instrument parameters and an unvalidated HIMF/evolution model. I agree with that identification. The abstract alone cannot support a quantitative BAO-viability claim; the qualitative ordering may survive, but the quantitative threshold claim is conditional on inputs that are not visible in the readable material. I therefore do not move the verdict: the paper remains UNVERDICTED, and the reader's low confidence is appropriate. The embedded line pointing to a different arXiv ID and category is flagged as in-scope evidence, but it is not itself the central technical weakness; it reinforces that the supplied full text cannot be used to verify the simulation inputs.","tokens_in":8561,"tokens_out":2925,"duration_ms":38517,"concrete_test":"Obtain the actual PDF or LaTeX source for arXiv:2508.16234 and locate the simulation parameters: Core Array Tsys/A_eff, baseline configuration, per-pointing integration time, sky coverage, and the adopted HIMF and its evolution. Recompute the z = 1 detection number density using (a) the stated parameters and (b) a conservative z = 0 ALFALFA-calibrated HIMF with no evolution, and compare both to the paper's declared BAO number-density threshold. If the no-evolution count falls below the threshold, the BAO claim rests entirely on assumed HIMF evolution; if either set of parameters is missing, the verdict remains UNVERDICTED.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is that the Core Array yields robust HI detections to z ~ 1 and a 'sufficient number density' for power-spectrum and BAO constraints. For this to hold, two coupled conditions must be true: (i) the modeled Core Array sensitivity and angular resolution — system temperature, effective area, baseline configuration, integration time, survey speed, overhead — are representative of the proposed instrument; and (ii) the z ~ 0.1–1 HI mass function and its evolution supply enough galaxies above the detection threshold. The abstract states neither, and the supplied full text is mojibake except for one embedded line pointing to arXiv:2508.16232v2 [eess.AS], a different paper ID and category. No validation against ALFALFA or other existing HI surveys is visible. The qualitative single-dish-vs-array ordering is plausible, but the quantitative z~1/BAO viability claim fails if the real array has lower sensitivity or survey speed than modeled, or if the high-redshift HIMF is lower than assumed. Moreover, 'sufficient number density' is a threshold judgment relative to a BAO error budget; it must be demonstrated, not asserted.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper uses semi-analytical simulations to compare the FAST single-dish mode and the proposed Core Array interferometry for HI galaxy redshift surveys in drift-scan (DS) and on-the-fly (OTF) modes. It reports that the single dish detects significant HI galaxies only at z ≲ 0.35 due to shot noise, while the Core Array should provide robust detections to z ∼ 1 and maintain a number density sufficient for power spectrum and BAO analyses. It also discusses cosmic variance at low z and survey-area/strategy trade-offs. However, in the submitted version the entire full text is rendered as unreadable mojibake, with one legible embedded line pointing to an unrelated arXiv identifier, so the quantitative basis for these claims cannot be checked.","tokens_in":8774,"tokens_out":6092,"duration_ms":64908,"significance":"If the quantitative claims are substantiated, the paper would be a valuable survey-strategy reference for FAST/Core Array, bridging single-dish and interferometric HI surveys for BAO cosmology. The comparative design—same simulated sky, two observing modes—is a meaningful, non-circular experiment, and the semi-analytical method is standard for such forecasts. However, the paper's central quantitative claims (z ∼ 1 detections, sufficient number density) are not supported in the accessible text and depend on unstated instrument and HIMF assumptions; the significance is therefore conditional until those inputs are documented and validated.","major_comments":[{"comment":"The entire body of the manuscript is unreadable (mojibake); the only legible embedded line, 'arXiv:2508.16232v2  [eess.AS]  8 Nov 2025', is an unrelated paper identifier in a different category. As submitted, none of the equations, tables, or model specifications can be checked. This is a load-bearing presentation failure, not a typo. Please resubmit a correctly encoded readable text, and remove/replace the unrelated arXiv line.","section":"Full text"},{"comment":"The central claims are quantified only by vague labels: 'significant HI detections at low redshifts (z ≲ 0.35)', 'robust HI galaxy detections up to z ∼ 1', and 'sufficient number density for power spectrum measurements and BAO constraints'. No detection S/N threshold, limiting flux or HI mass, number density n(z), or nP value is given in the abstract, and the body is unreadable. Specify the assumed Core Array sensitivity parameters (A_eff/T_sys, baselines, integration time, survey speed), the resulting n(z) at z ~ 1, and the S/N criterion used for 'robust'.","section":"Abstract"},{"comment":"'Sufficient number density' is a threshold judgment relative to a BAO error budget. The manuscript does not state this threshold or show that the forecasted number density exceeds it. Provide the forecasted nP at k ~ 0.2 h Mpc^-1 for z ~ 1, or a Fisher-matrix BAO/DETFOM error, or clearly label the statement as a qualitative heuristic. Without this, the headline claim is not falsifiable.","section":"Abstract/Results"},{"comment":"The comparison of two modes on the same simulated sky is methodologically sound. However, the absolute z ~ 1 detection yields depend on the assumed HI mass function and its evolution. The visible text contains no validation against ALFALFA or other HI surveys. Add a calibration paragraph showing the simulated low-z HIMF reproduces ALFALFA, and justify the high-z HIMF choice against current constraints or clearly frame the result as an optimistic scenario.","section":"Semi-analytical simulations / model inputs"}],"minor_comments":[{"comment":"The statement that increasing survey area 'has little impact' on single-dish observations would benefit from specifying the tested areal range (e.g., in deg^2) for both DS and OTF modes.","section":"Abstract"}],"recommendation":"major_revision","confidential_remarks":"The uploaded text appears corrupted; consider asking the authors to provide a clean PDF before external review. The embedded arXiv ID 2508.16232v2 [eess.AS] is unrelated and should not appear in any version. Given the present file, the paper cannot be evaluated; my recommendation of major_revision assumes a readable resubmission becomes available."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: this is a plausible and potentially useful instrument-planning forecast, but I could not verify the numbers because the full text provided to me is mojibake. The abstract makes sense on its own terms, and the qualitative ordering — single-dish FAST shot-noise limited past z~0.35, Core Array pushing robust detections to z~1 — follows from standard sensitivity arguments. That ordering is likely correct.\n\nWhat's new: a configuration-specific comparison (single-dish vs Core Array, DS vs OTF, out to z~1) for a proposed instrument that doesn't yet have a survey-mode literature. That is worth having. The authors simulate both modes on the same sky, which is a meaningful comparison, not an identity.\n\nSoft spots, in proportion. The central claim — 'sufficient number density for power spectrum and BAO constraints' — is asserted without stating the instrument parameters (system temperature, effective area, survey speed) or the HI mass function used. That makes the quantitative result conditional. If the real array is dimmer or the high-redshift HIMF is lower than modeled, the z~1 claim fails even though the single-dish/array ordering survives. Also, 'sufficient' is a threshold relative to a BAO error budget; it needs to be demonstrated. Second, the provided full text is unreadable mojibake except for one embedded line pointing to a different arXiv paper (2508.16232v2, eess.AS). That is a provenance red flag and means I cannot check validation against ALFALFA or any cited external data. This is not necessarily the authors' fault, but it blocks verification. Finally, the abstract alone carries the 'robust detections up to z~1' language with no detection-limit or number-density numbers; those need to be in the abstract or at least in a visible figure.\n\nFor whom: anyone planning HI surveys with FAST or the proposed Core Array, and people who build survey-forecast tools. If the actual paper contains the usual sensitivity tables, HIMF references, and a BAO threshold calculation, it deserves publication. I'd send it to a referee who knows both interferometric sensitivity and HI galaxy surveys. I just can't sign off on the specifics from the material I received.","headline":"A plausible and potentially useful survey-strategy forecast for FAST vs its proposed Core Array, but the z~1/BAO claim rests on unstated inputs and the provided full text is unreadable.","tokens_in":9331,"tokens_out":3030,"would_cite":false,"duration_ms":32926,"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":"The paper argues that FAST's proposed Core Array interferometry keeps HI galaxy surveys dense enough for BAO constraints out to z ≈ 1, while the single-dish mode is limited to z ≈ 0.35 by shot noise.","keywords":["21-cm HI galaxy surveys","FAST Core Array interferometry","single-dish versus interferometer survey strategies","shot noise","baryon acoustic oscillations","drift scan and on-the-fly observing","semi-analytical simulation","HI cosmology"],"falsifier":"Measure the actual noise and point-source sensitivity of the assembled Core Array, then run a deep targeted observation in a small patch at z ≈ 0.5–1 and count detections; if the observed number density falls below the simulated value at the survey's detection threshold, the 'sufficient number density' claim for BAO constraints is falsified. A null at z ≈ 1 despite the modeled sensitivity would directly undermine the headline result, while leaving the low-z single-dish survey unaffected.","tokens_in":8410,"feed_emoji":"📡","tokens_out":4617,"duration_ms":51404,"temperature":0.7,"pith_summary":"The paper uses semi-analytical simulations to compare two ways of running an HI galaxy survey with FAST: the single-dish mode and the proposed Core Array interferometer. It claims the single-dish mode works only at low redshift (z ≲ 0.35) because shot noise destroys the sample at higher redshifts, whereas the Core Array's higher sensitivity and angular resolution retains enough galaxies out to z ≈ 1 to measure the 21-cm power spectrum and constrain baryon acoustic oscillations. The practical claim is that, if the Core Array is built as modeled, FAST becomes a high-redshift HI galaxy survey instrument rather than a low-redshift one. The choice between drift-scan and on-the-fly observing trades sky coverage against depth, and at the lowest redshifts cosmic variance, not detector sensitivity, dominates the error budget. This matters because a z ~ 1 HI galaxy survey would provide an independent, 21-cm-selected probe of large-scale structure and dark energy.","feed_headline":"Core Array extends FAST HI surveys to z ~ 1","feed_subtitle":"The single dish hits a shot-noise wall by z≈0.35; the interferometric upgrade keeps enough galaxies for BAO constraints.","key_machinery":"The comparison machinery is a semi-analytical simulation of HI galaxies passed through two instrument models: FAST single-dish and FAST Core Array interferometry, each run in drift-scan and on-the-fly modes. The load-bearing outputs are the detected galaxy number density as a function of redshift, the shot-noise level in the 21-cm power spectrum, and the resulting BAO constraints. The Core Array's higher sensitivity and angular resolution is what relieves shot noise at high redshift, while the drift-scan versus on-the-fly distinction is the survey-strategy handle that trades sky area against integration depth.","core_discovery":"The central claim is that the FAST Core Array interferometry makes HI galaxy redshift surveys viable to z ~ 1, whereas the FAST single-dish mode is limited to z ≲ 0.35. Using semi-analytical simulations, the paper compares galaxy number density, shot noise, and the resulting power-spectrum and BAO constraints across redshifts and observing modes. At z ~ 0.01–0.08 both configurations perform well and cosmic variance dominates; at z > 0.35 only the Core Array keeps a sufficient number density, and enlarging the survey area does little for the single dish because its problem is shot noise, not sky coverage. The paper therefore establishes the Core Array as the enabling mode for high-redshift HI","pith_inferences":["I read the paper as motivating a split strategy it does not itself propose: a wide, shallow drift-scan for z ≲ 0.35 plus a deep on-the-fly Core Array field at z ~ 0.5–1 would cover both cosmology regimes efficiently with one instrument.","A direct observational test beyond the paper's simulations would be to run a small pathfinder field with the actual Core Array at z ~ 0.5–1, count HI detections, and compare with the simulated number density before committing to a full survey.","Because the high-redshift result leans on the modeled evolution of the HI mass function, recomputing the forecasts with pessimistic and optimistic envelopes of that evolution would show whether the 'sufficient number density' conclusion is robust even if the single-dish-versus-array ordering likely survives."],"forward_implications":["If the simulations are right, the Core Array, not the single dish, should be the default instrument for FAST surveys targeting HI galaxies at z > 0.35.","A z ~ 1 HI galaxy sample dense enough for power-spectrum measurement would let BAO and large-scale-structure constraints be drawn from 21-cm-selected galaxies, complementing optical surveys.","At z < 0.1, cosmic variance sets the error floor, so extra integration time or area buys little at those redshifts.","Drift-scanning gives wide sky coverage but is tied to Earth's rotation; on-the-fly mapping trades that for pointed deep fields, so the two strategies serve different survey goals."],"supporting_citations":[],"fun_headline_variants":["FAST's Core Array maps HI galaxies out to redshift 1","Interferometry lets FAST see HI galaxies at z ~ 1","HI survey to z=1 needs FAST's interferometer, not single dish","Core Array gives FAST the sensitivity to see HI at z~1","FAST's interferometer beats shot noise for high-z HI surveys"],"cache_read_input_tokens":2688,"weakest_assumption_plain":"The z ~ 1 claim rests on the assumed Core Array sensitivity and noise, plus the simulated abundance of HI galaxies at z = 0.1–1; if the real array is dimmer or high-redshift HI galaxies are rarer than modeled, the claimed number density and BAO feasibility fail even though the qualitative single-dish-versus-array ordering may survive.","fun_headline_variants_meta":{"raw":{"variants":["FAST's Core Array maps HI galaxies out to redshift 1","Interferometry lets FAST see HI galaxies at z ~ 1","HI survey to z=1 needs FAST's interferometer, not single dish","Core Array gives FAST the sensitivity to see HI at z~1","FAST's interferometer beats shot noise for high-z HI surveys"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000769,"raw_usage":{"total_tokens":3281,"prompt_tokens":817,"completion_tokens":2464,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":561,"completion_tokens_details":{"reasoning_tokens":2371}},"tokens_in":561,"tokens_out":2464,"duration_ms":17254,"temperature":1.0,"reasoning_tokens":2371,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-05T17:25:49.485128+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the actual noise and point-source sensitivity of the assembled Core Array, then run a deep targeted observation in a small patch at z ≈ 0.5–1 and count detections; if the observed number density falls below the simulated value at the survey's detection threshold, the 'sufficient number density' claim for BAO constraints is falsified. A null at z ≈ 1 despite the modeled sensitivity would directly undermine the headline result, while leaving the low-z single-dish survey unaffected.","supporting_citations":[],"review_version":1}