{"id":"eeca9bdf-3e2a-48f0-bcc7-8fe351caea71","arxiv_id":"2507.11765","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"A calibration of the Tully-Fisher relation using DESI Survey Validation data yields a slope of -7.96±0.13 and a zero-point of -19.34(+0.30,-0.29) AB mag, enabling a 1,136-galaxy peculiar velocity catalog.","lead":"DESI's Peculiar Velocity Survey used single-point fiber measurements of 1,163 spiral galaxies to measure the Tully-Fisher relation, which links a galaxy's rotation speed to its brightness. The team calibrated the relation using the Coma Cluster and two supernovae-calibrated galaxies, producing the first catalog of galaxy distances based on rotation speeds measured at a single point in each disk.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Zero-point rests on only two SN Ia calibrators; the quoted ±0.30 mag uncertainty omits the 1.07 mag TFR scatter, so the absolute distance scale for all 1136 galaxies may carry an unquoted ~0.7 mag floor.","rationale":"The central claim is that a single-fiber 0.33R26 velocity measurement yields a viable TFR with the quoted slope and zero-point. The slope is anchored by 41 Coma galaxies and has partial independent support from the CF4 cross-match, but the zero-point is the load-bearing link between the TFR and absolute distances. With only two SN Ia hosts, the zero-point is fragile: the hosts span a limited velocity range, both sit on the same side of the adopted relation, and the quoted uncertainty mirrors only the SN distance-modulus errors. The 1.07 mag intrinsic scatter alone forces a ~0.76 mag floor on the zero-point standard error for N = 2, so the quoted ±0.30 mag overstates the calibration. This does not require rejecting the catalog; the paper is transparent, the code and data are public, and the CF4 comparison is a useful independent check if quantified. A reanalysis of the two calibrators including the scatter will settle whether the concern lands. This matches the reader's weakest assumption, so the conditional verdict stands.","tokens_in":22630,"tokens_out":24545,"duration_ms":308574,"concrete_test":"Recompute b_0pt from the two Table 2 hosts using Eq. 19 with a fixed at the reported -7.96 and V0 = 10^2.01 km/s, propagating both the SN distance-modulus errors and the 1.07 mag TFR scatter through a two-point likelihood. If the resulting 68% interval on b_0pt is wider than ±0.30 mag (expected to be roughly ±0.76 mag or larger), then the reported zero-point precision is not supported and the absolute distance scale of the 1136-galaxy catalog is correspondingly uncertain.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Section 5.3 fixes the TFR slope from 41 Coma galaxies and the zero-point b_0pt from exactly two SN Ia hosts in Table 2. Using Eq. 19 with a = -7.96, b_0pt = -19.34, and V0 = 10^2.01 km/s, the residuals for the two hosts are M_obs - (b_0pt + a log10(V/V0)) ≈ +0.50 mag (SGA 294387) and +0.89 mag (SGA 464075); both fall on the same side of the adopted relation. The weighted mean zero-point implied by the two hosts alone is about -18.5 to -18.6, not -19.34, so the reported value is roughly 0.7 mag brighter than the calibrators indicate. The quoted +0.30/-0.29 mag uncertainty reflects only the SN distance-modulus errors. With a reported intrinsic scatter of σ_Coma = 1.07 mag and N = 2 calibrators, the standard error of the zero-point mean is at least σ/sqrt(N) ≈ 0.76 mag, and larger if the two hosts are unrepresentative. Thus all 1136 distance moduli and peculiar velocities inherit a systematic floor of order 0.7-0.8 mag that is not included in the quoted zero-point uncertainty. The joint fit's assumption of a common Coma/SN-host slope cannot be tested with only two SN points; the slope between the two hosts is about -6.4, compared to the adopted -7.96, so a slope mismatch is partially degenerate with the zero-point offset. The CF4 comparison in Fig. 11 is presented qualitatively and does not quote a mean offset or a trend, so it does not currently resolve the issue.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper calibrates the Tully-Fisher relation (TFR) using DESI Early Data Release observations from the DESI Peculiar Velocity Survey. Rotational velocities are measured at 0.33R26 from single fibers placed on the centers and major axes of spiral galaxies from the Siena Galaxy Atlas. The slope is calibrated with 41 Coma cluster members and the zero-point with two galaxies having Type Ia supernova distances from the Extragalactic Distance Database. The authors report an r-band slope of -7.96±0.13 mag, a zero-point of -19.34(+0.30,-0.29) mag, and an intrinsic scatter of 1.07±0.02 mag, and they use this calibration to produce a catalog of distances and peculiar velocities for 1136 galaxies. The analysis includes comparisons of DESI rotational velocities with MaNGA rotation-curve fits and a comparison of the calibrated TFR with Cosmicflows-4.","tokens_in":22969,"tokens_out":4462,"duration_ms":58432,"significance":"If the calibration is sound, this is the first catalog of Tully-Fisher distances based on single-disk-point velocity measurements, and it provides a valuable proof of concept for the full DESI PV Survey. The public catalog and the detailed comparison with MaNGA velocity fields are concrete strengths: the MaNGA comparison in Section 4.1 quantifies the scatter introduced by measuring velocities at 0.33R26 rather than at the flat part of the rotation curve, and the machine-readable catalog in Table 3 will be useful to the community. However, the absolute distance scale and all 1136 peculiar velocities depend on a zero-point calibrated with only two SN Ia host galaxies; the quoted zero-point uncertainty does not currently include the dominant TFR scatter contribution, so the central calibration claim is not yet fully supported.","major_comments":[{"comment":"The zero-point rests on exactly two galaxies with SN Ia distances, and the quoted uncertainty of +0.30/-0.29 mag does not include the reported intrinsic scatter of σ_Coma = 1.07 mag. With N=2 calibrators, the standard error of the zero-point mean is at least σ/sqrt(N) ≈ 0.76 mag even before considering systematics, so the stated uncertainty is underestimated by a factor of roughly 2.5. In addition, using the values in Table 2 and Eq. (19) with the adopted slope a=-7.96 and V0=10^2.01 km/s, both galaxies fall on the same side of the fitted relation (residuals of about +0.50 and +0.89 mag); their weighted-mean implied zero-point is approximately -18.5, about 0.8 mag brighter than the reported -19.34. The authors should report a zero-point uncertainty that includes the TFR scatter contribution and should explicitly discuss the apparent offset between the reported zero-point and the two calibrators.","section":"§5.3, Table 2, Eq. (19)"},{"comment":"The joint fit assumes that the Coma cluster galaxies and the two SN Ia host galaxies follow the same TFR slope, but this assumption cannot be tested with only two zero-point calibrators. The slope implied by the two SN hosts alone is about -6.4, compared with the adopted Coma-based slope of -7.96; a slope difference of this magnitude is partially degenerate with the zero-point offset. The paper should either add independent calibrators with distances (e.g., Cepheid or SBF distances from the EDD that pass the quality cuts, if any are available) or demonstrate through a sensitivity analysis how much the zero-point and final distances change for plausible slope differences between the populations.","section":"§5.3, Fig. 8"},{"comment":"The comparison with Cosmicflows-4 is presented only qualitatively as \"excellent agreement,\" with no quoted mean offset, RMS scatter, or test for a trend in the residual as a function of rotational velocity. Given that the zero-point anchor is weak, this comparison is the most direct available external check and should be quantified: report the mean and scatter of (M_DESI - M_CF4) for the 56 overlap galaxies, and check whether any residual trend with log V or apparent magnitude exists. Without these numbers, Fig. 11 does not currently resolve the zero-point concern.","section":"§7.1, Fig. 11"},{"comment":"The distance moduli and peculiar velocities in the catalog inherit any zero-point uncertainty, but the table entries and the quoted V_pec errors do not appear to include the ~0.7-0.8 mag zero-point floor identified above. For example, the first row of Table 3 quotes µ = 33.32±0.92 and V_pec = 3100±3000 km/s; if the zero-point systematic is added, the distance modulus uncertainty and the resulting peculiar velocity uncertainties will increase substantially. The paper should state explicitly which uncertainties are propagated into the catalog and provide a recommendation on how users should treat the zero-point systematic when using the published peculiar velocities.","section":"§6, Table 3"}],"minor_comments":[{"comment":"The 22% scatter in the perpendicular-distance distribution is quoted without a confidence interval; given that this quantity is used to interpret σ_Coma, a bootstrap or similar uncertainty would be helpful.","section":"§4.1.3, Fig. 5"},{"comment":"The notation b_Coma is described as a y-intercept, but Eq. (19) uses it as the intercept at log(V/V0)=0; a sentence clarifying that both b_Coma and b_0pt are defined at V0 would avoid ambiguity.","section":"§5.3, Eq. (19)"},{"comment":"The text says that of 11 galaxies with EDD distances only two satisfy the quality criteria, but it does not state how many of the 11 have SN Ia distances versus other distance indicators; this information would help readers understand whether additional zero-point calibrators could be added with different cuts.","section":"§5.2"},{"comment":"The large scatter toward negative peculiar velocities at low rotational velocity is attributed to interacting systems and misaligned position angles; a quantitative flag or warning column in the catalog for galaxies more than 2σ from the TFR would make this recommendation actionable.","section":"§6, Fig. 10"},{"comment":"The title and abstract contain minor typographical artifacts (e.g., \"T ully-Fisher\" and \"V elocity\" in the typeset version); these should be corrected in the final journal version.","section":"Title/Abstract"}],"recommendation":"major_revision","confidential_remarks":"The paper is a reasonable fit for the journal and the underlying observational program is valuable. My recommendation of major revision is driven by the zero-point calibration: with only two SN Ia calibrators and a quoted uncertainty that excludes the 1.07 mag TFR scatter, the absolute distance scale is not yet established at the claimed precision. The comparison with Cosmicflows-4 could have provided a strong external check but is currently only qualitative. If the authors add a realistic zero-point uncertainty budget, quantify the CF4 comparison, and discuss the apparent offset between the two calibrators and the adopted zero-point, the paper would be suitable for publication."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: this is the first TFR peculiar-velocity catalog built from single-point disk velocities, and that is a real milestone for the DESI PV program. But the zero-point does not hold up. The stress-test arithmetic checks out: the two SN Ia calibrators in Table 2 sit 0.50 and 0.89 mag above the adopted relation, implying a zero-point around -18.5 rather than the reported -19.34. That is a roughly 0.7 mag discrepancy, and it is not captured by the quoted +0.30/-0.29 uncertainty, which only reflects SN distance-modulus errors. With two calibrators and 1.07 mag intrinsic scatter, the statistical floor alone is sigma/sqrt(N) about 0.76 mag. All 1136 distance moduli and peculiar velocities inherit this floor. What the paper does well: the method is transparent, the quality cuts are sensible, and the comparison with MaNGA rotation-curve fits is a genuine attempt to quantify the scatter introduced by measuring at 0.33R26. The slope calibration from 41 Coma galaxies is distance-independent and the fitted slope -7.96 +/- 0.13 is plausible. Releasing the catalog and example code on Zenodo is the right move. The claim of being the first TFR catalog using single-point velocities is credible. The soft spots are concentrated in the zero-point, and they are load-bearing. The joint fit assumes Coma and SN-host galaxies share the same slope, but with only two SN hosts that assumption cannot be tested. The CF4 comparison in Fig. 11 is qualitative, does not quote a mean offset, and cannot resolve a 0.7 mag scale error. There is also no simulation validation of the HyperFit join, which would at least show how the two-host zero-point behaves under realistic scatter. None of this is fatal to the concept, but the catalog as released should not be used for cosmological PV measurements until the zero-point is revisited with a larger SN sample or an independent distance anchor. Who is this for? People working on peculiar velocities and growth-of-structure forecasts. It is a useful proof-of-concept and a well-written technical description of the DESI TFR pipeline. But a serious referee should demand a re-analysis of the zero-point, a residual table for the two calibrators, and an explicit statement of the systematic floor. I would send it to review, but with expectation of major revision.","headline":"First single-point TFR catalog is a real milestone for DESI, but the zero-point is inconsistent with its own two SN Ia calibrators by about 0.7 mag, and that floor is missing from the quoted uncertainty.","tokens_in":671,"tokens_out":1691,"would_cite":false,"duration_ms":48017,"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":"Using only single-point fiber spectra, DESI calibrates a Tully-Fisher relation that yields distances and peculiar velocities for 1,136 spiral galaxies.","keywords":["Tully-Fisher relation","peculiar velocities","DESI","galaxy rotation curves","spiral galaxies","distance indicators","Coma Cluster"],"falsifier":"Recalibrate the zero point using a third independent supernova-host galaxy and check whether it moves by more than the quoted roughly 0.3 AB mag uncertainty. Alternatively, compare the catalog distances against a sample with Cepheid or surface-brightness-fluctuation distances and see whether the mean log-distance ratio deviates from zero.","tokens_in":22399,"feed_emoji":"🌀","tokens_out":7938,"duration_ms":80314,"temperature":0.7,"pith_summary":"This paper shows that a single spectroscopic fiber placed on a spiral galaxy's disk — at $0.33R_{26}$, where $R_{26}$ is the radius of the 26 mag arcsec$^{-2}$ r-band isophote — measures a rotation velocity accurate enough to calibrate the Tully-Fisher relation and derive distances. From 41 Coma Cluster galaxies the authors fit a slope of $-7.96 \\pm 0.13$ AB mag and a scatter of $1.07 \\pm 0.02$ AB mag; two galaxies with type-Ia-supernova distances fix the zero point at $-19.34^{+0.30}_{-0.29}$ AB mag. The resulting public catalog gives distances and peculiar velocities for 1,136 spiral galaxies, the first catalog of TFR distances produced from velocities measured at a single point in each disk. The result matters because it validates a fast observational route to peculiar velocities, which the full DESI survey will extend to more than 50,000 disk galaxies.","feed_headline":"Single-point fiber speeds calibrate Tully-Fisher for 1,136 galaxies","feed_subtitle":"DESI measured each galaxy's rotation from one fiber in the disk, opening a path to 50,000 peculiar velocities.","key_machinery":"The load-bearing object is the single-point rotational velocity measured at $0.33R_{26}$, the radius of the 26 mag arcsec$^{-2}$ $r$-band isophote from the Siena Galaxy Atlas. A fiber on the galaxy center gives the systemic redshift; fibers on either side give the line-of-sight rotation component, which is divided by $\\sin i$ using photometric inclinations and averaged across the two sides. The calibration is a joint HyperFit of 41 Coma galaxies and two type-Ia-supernova-calibrated galaxies, with dwarf galaxies removed iteratively and galaxies volume-weighted to undo the size-limited sample selection.","core_discovery":"The discovery is that DESI's Early Data Release spectra, taken with fibers at the center and at $\\pm 0.33R_{26}$ along each galaxy's major axis, recover the Tully-Fisher relation with a slope $-7.96\\pm0.13$ AB mag in the $r$-band, a zero point $-19.34^{+0.30}_{-0.29}$ AB mag, and an intrinsic scatter of $1.07\\pm0.02$ AB mag. The authors validate these rotation velocities against resolved MaNGA rotation-curve fits for 55 galaxies, and they find close agreement with the Cosmicflows-4 TFR calibration for the 56 galaxies in common. They interpret the measured power-law slope of $3.18\\pm0.05$ as the expected consequence of measuring at $0.33R_{26}$, where rotation curves have not fully flattened, consistent with existing results that the TFR slope steepens with radius.","pith_inferences":["A natural next test is whether the two supernova-calibrated galaxies actually lie on the same TFR as the Coma population; a slope difference between the two groups would silently bias the zero point.","Later DESI data will allow a multi-cluster slope calibration, replacing Coma's own velocity dispersion with a more robust anchor.","The main survey's move from $0.33R_{26}$ to $0.4R_{26}$ offers a direct empirical test of the claim that the TFR slope steepens with radius.","The peculiar velocities could be cross-correlated with density-field reconstructions; large-scale coherent residuals would reveal whether single-point rotation velocities carry a redshift-dependent bias."],"forward_implications":["The full five-year DESI survey, using fibers at $0.4R_{26}$, can build more than 50,000 TFR-based peculiar velocities with the same single-point technique.","The public catalog of 1,136 distances can be combined with DESI Fundamental-Plane peculiar velocities to map the local velocity field and constrain $f\\sigma_8$.","Because the TFR slope at $0.33R_{26}$ is $-7.96\\pm0.13$ AB mag, slopes from different surveys must be compared at matched measurement radii.","The measured scatter of $1.07\\pm0.02$ AB mag is expected to shrink as the fiber placement moves outward in later DESI data."],"supporting_citations":[{"why":"Defines the luminosity-rotation-velocity relation that the paper calibrates.","marker":"Tully & Fisher 1977"},{"why":"Designs the DESI PV Survey and sets the 0.33 R26 fiber placement used here.","marker":"Saulder et al. 2023"},{"why":"Supplies the SGA-2020 photometry, sizes, and axis ratios for target selection and magnitudes.","marker":"Moustakas et al. 2023"},{"why":"Provides the calibration scheme (slope from cluster, zero point from independent distances) and the Cosmicflows-4 TFR used for comparison.","marker":"Kourkchi et al. 2020a"},{"why":"Provides the type-Ia-supernova distance moduli that fix the zero point.","marker":"Stahl et al. 2021"},{"why":"Supplies MaNGA rotation-curve fits used to check the 0.33 R26 velocity measurements.","marker":"Ravi et al. 2024"},{"why":"Gives the estimator used to convert TFR distances into peculiar velocities.","marker":"Watkins & Feldman 2015"},{"why":"Justifies calibrating the TFR at any galactocentric radius and predicts the slope depends on that radius.","marker":"Yegorova & Salucci 2007"},{"why":"Provides HyperFit, the fitting engine for the joint slope and zero-point calibration.","marker":"Robotham & Obreschkow 2015"},{"why":"Describes the Survey Validation observations that make up the DESI Early Data Release used here.","marker":"DESI Collaboration et al. 2024b"}],"fun_headline_variants":["Single-fiber rotation measures calibrate Tully-Fisher for 1,136 galaxies","DESI's one-point rotation speeds pin down Tully-Fisher","Tully-Fisher calibrated from 1,136 single-fiber galaxy spins","One fiber per galaxy yields precise Tully-Fisher calibration","First Tully-Fisher catalog from DESI single-point velocities"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The entire distance scale hangs on the two galaxies with type-Ia-supernova distances that fix the zero point; if either distance modulus, the SGA photometry, or the rotation velocity of these two galaxies is systematically wrong, all 1,136 distance measurements shift with it.","fun_headline_variants_meta":{"raw":{"variants":["Single-fiber rotation measures calibrate Tully-Fisher for 1,136 galaxies","DESI's one-point rotation speeds pin down Tully-Fisher","Tully-Fisher calibrated from 1,136 single-fiber galaxy spins","One fiber per galaxy yields precise Tully-Fisher calibration","First Tully-Fisher catalog from DESI single-point velocities"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000604,"raw_usage":{"total_tokens":2849,"prompt_tokens":1010,"completion_tokens":1839,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":626,"completion_tokens_details":{"reasoning_tokens":1745}},"tokens_in":626,"tokens_out":1839,"duration_ms":15456,"temperature":1.0,"reasoning_tokens":1745,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T17:00:52.409267+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Recalibrate the zero point using a third independent supernova-host galaxy and check whether it moves by more than the quoted roughly 0.3 AB mag uncertainty. Alternatively, compare the catalog distances against a sample with Cepheid or surface-brightness-fluctuation distances and see whether the mean log-distance ratio deviates from zero.","supporting_citations":[{"cited_title":"A., & Demina, R","cited_arxiv_id":null,"evidence_quote":"Supplies MaNGA rotation-curve fits used to check the 0.33 R26 velocity measurements."}],"review_version":1}