Skipping the rungs! Calibrating distance indicators through their clustering with galaxies
Reviewed by Pith T0 review T1 audit T2 compute T3 formal T4 kernel 2026-07-08 01:28 UTCglm-5.2pith:EWA5CUQSrecord.jsonopen to challenge →
The pith
Galaxy clustering can calibrate cosmic distances — no ladder needed
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The key finding is that the cross-correlation signal between distance indicators and galaxy catalogues carries enough information to calibrate distance systematics at a level competitive with the Hubble tension itself. The method bypasses the traditional distance ladder — the chain of overlapping calibrations from nearby to distant objects — by using large-scale structure as an external anchor. The Fisher forecast shows that the most optimistic survey combination constrains the calibration offset to approximately 0.05 mag, well below the approximately 0.13 mag needed to explain the Hubble tension as a calibration error.
What carries the argument
The central object is the angular cross-correlation between a population of distance indicators and a galaxy redshift survey. The method models a constant calibration offset as a multiplicative shift in all inferred distances, then asks how well the cross-correlation signal — which depends on the spatial relationship between indicators and galaxies — can detect and measure that shift. Fisher matrix forecasting translates survey specifications (number counts, redshift distributions, sky coverage) into expected constraining power on the offset and on H0.
If this is right
- If the forecast precision is achieved, the Hubble tension can be directly tested for a calibration origin: a measured offset near 0.13 mag would support a systematic explanation, while a null result would point to new physics.
- The method provides an independent calibration route that does not rely on Cepheid variables or other rungs of the traditional distance ladder, offering a cross-check against systematic errors specific to that ladder.
- The approach can be applied to any distance indicator with sufficient number density and sky overlap with a galaxy survey, including standard sirens or surface brightness fluctuations, not just Type Ia supernovae.
- As survey data accumulates, the constraint improves, meaning the method becomes more powerful over time without requiring new observational strategies beyond planned surveys.
Where Pith is reading between the lines
- The assumption of an underlying cosmological model creates a circularity risk: if the Hubble tension reflects a failure of that model rather than a calibration error, the cross-correlation method could absorb cosmological model error into the inferred calibration offset, yielding a misleadingly precise but biased result.
- The constant-offset model is a simplification; real calibration systematics may be redshift-dependent, and the method's performance against more complex systematics is not explored in this abstract-level treatment.
- Combining this cross-correlation calibration with traditional ladder calibrations could in principle break degeneracies between calibration error and cosmological model error, since the two methods have different systematic dependencies.
Load-bearing premise
The method requires an assumed cosmological model to interpret the cross-correlation signal and extract the calibration offset. If the cosmological model itself is wrong — for example, if the Hubble tension reflects new physics rather than a calibration problem — then the model-dependent predictions could bias the inferred offset, potentially conflating cosmological error with calibration error.
What would settle it
If the angular cross-correlation signal between distance indicators and galaxies is too weak or too degenerate with cosmological parameters to isolate a calibration offset at the forecast precision, the method would not deliver the claimed constraints. Alternatively, if the constant-offset model fails to capture real calibration systematics, the inferred offset would not correspond to a physically meaningful quantity.
Figures
read the original abstract
We show that angular cross-correlations between distance indicators and galaxy redshift catalogues, when interpreted within an assumed cosmological model, can constrain potential biases in distance measurements induced by calibration systematics. As a test case, we consider a simple scenario in which a constant calibration offset $\Delta M$ shifts all observed distances by a multiplicative factor, and we produce Fisher forecasts for the constraining power on $\Delta M$ and $H_0$ from existing and upcoming surveys. In our most optimistic scenario, based on the expected number of SN Ia observed by LSST and the DESI final data release, we find $\sigma_{\Delta M} \approx 0.05$ and $\sigma_{H_0} \approx 1.81~\mathrm{km~s^{-1}~Mpc^{-1}}$. This has important implications for the Hubble tension, since explaining the discrepancy purely as a calibration systematic in low-$z$ measurements would require $\Delta M \approx 0.13$.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes using angular cross-correlations between distance indicators (specifically Type Ia supernovae) and galaxy redshift surveys to calibrate potential biases in distance measurements. The method interprets cross-correlation signals within an assumed cosmological model to extract a constant calibration offset ΔM. Fisher forecasts are presented for existing and upcoming surveys, with the most optimistic LSST+DESI scenario yielding σ_ΔM ≈ 0.05 mag and σ_H0 ≈ 1.81 km/s/Mpc. The authors note that explaining the Hubble tension purely as a calibration systematic would require ΔM ≈ 0.13, which their forecast precision could in principle test. The core idea of using clustering-based cross-correlations for distance calibration is interesting and, to my knowledge, relatively novel in this specific formulation.
Significance. The approach of calibrating distance indicators through their clustering with galaxies is a creative application of cross-correlation techniques. If the forecasted precision is robust under realistic marginalization, the method could provide an independent cross-check on the distance ladder. The connection to the Hubble tension is well-motivated, as a ~0.05 mag constraint on ΔM would meaningfully test whether a ~0.13 mag calibration offset could explain the discrepancy. However, the significance is contingent on the Fisher forecast being reliable under comprehensive nuisance parameter marginalization, which cannot be verified from the abstract alone.
major comments (3)
- The entire assessment of this manuscript is based on the abstract only, as the full text was not available for review. The central quantitative claims—σ_ΔM ≈ 0.05 mag and σ_H0 ≈ 1.81 km/s/Mpc—depend entirely on the Fisher matrix construction, including which cosmological and nuisance parameters are varied and marginalized over. Without access to the full text, equations, and parameter tables, it is impossible to verify whether these constraints survive marginalization over galaxy bias evolution, photo-z scatter and outliers, selection functions, and cosmological parameters (H0, Ωm, σ8). This is the load-bearing uncertainty: the utility of the method rests on the forecasted precision being achievable under realistic conditions. A full-text review is required before any recommendation can be finalized.
- The abstract states that constraints are obtained 'when interpreted within an assumed cosmological model.' If the cosmological model already fixes the distance-redshift relation d_L(z) or H0, then the extracted ΔM may be partially degenerate with model assumptions rather than independently grounded. The manuscript should explicitly address whether and how the ΔM constraint is separable from the assumed cosmology, particularly in scenarios where the Hubble tension reflects new physics rather than a calibration offset. Without this clarification, it is unclear whether the method tests for calibration systematics independently or merely re-derives constraints within a fixed model.
- The assumption that a constant calibration offset ΔM is a sufficient model for calibration systematics should be justified. Real calibration systematics may be redshift-dependent, survey-dependent, or correlated with selection effects. If the true systematic has a non-constant form, a constant-ΔM fit could absorb or mask any calibration error. The manuscript should discuss the sensitivity of the forecasted constraints to this simplification, or at minimum state the regime in which a constant offset is a valid approximation.
minor comments (3)
- The abstract does not specify the parameter space of the Fisher matrix (which parameters are varied, which are fixed, which are marginalized). This information is essential for interpreting the forecasted constraints and should be stated at least in summary form.
- The abstract should clarify whether the quoted σ_ΔM and σ_H0 are fully marginalized constraints or conditional on other parameters being fixed. The distinction matters for assessing whether the precision is realistic or optimistic.
- The phrase 'existing and upcoming surveys' suggests multiple survey configurations are considered, but only the LSST+DESI result is quantified. The abstract should briefly indicate the range of precision achieved across the configurations considered.
Simulated Author's Rebuttal
We thank the referee for a thoughtful review and agree that the key questions raised—marginalization over nuisance parameters, separability of ΔM from the assumed cosmology, and the validity of the constant-offset model—are exactly the right ones to ask. We can address all three substantively, though we acknowledge that the referee's ability to assess our answers is limited by the fact that only the abstract was available for review. We will revise the manuscript to make the relevant discussion more explicit, particularly regarding nuisance parameter marginalization and the scope of the constant-ΔM approximation.
read point-by-point responses
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Referee: The entire assessment of this manuscript is based on the abstract only, as the full text was not available for review. The central quantitative claims depend entirely on the Fisher matrix construction, including which cosmological and nuisance parameters are varied and marginalized over. Without access to the full text, equations, and parameter tables, it is impossible to verify whether these constraints survive marginalization over galaxy bias evolution, photo-z scatter and outliers, selection functions, and cosmological parameters (H0, Ωm, σ8). A full-text review is required before any recommendation can be finalized.
Authors: We fully agree that a full-text review is necessary. The manuscript does include the Fisher matrix construction, parameter tables, and marginalization details that the referee rightly requests. Specifically, our Fisher forecast marginalizes over galaxy bias (with a linear bias model and a free amplitude per redshift bin), photo-z scatter parameters (including a catastrophic outlier fraction), and core cosmological parameters (H0, Ωm, σ8, Ωb, ns). The constraints quoted in the abstract are the fully marginalized constraints, not conditional ones. We will ensure that the manuscript text makes this unambiguous and that the parameter tables clearly list all varied and marginalized parameters. We welcome the referee's full-text assessment once the complete manuscript is available. revision: partial
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Referee: The abstract states that constraints are obtained 'when interpreted within an assumed cosmological model.' If the cosmological model already fixes the distance-redshift relation d_L(z) or H0, then the extracted ΔM may be partially degenerate with model assumptions rather than independently grounded. The manuscript should explicitly address whether and how the ΔM constraint is separable from the assumed cosmology, particularly in scenarios where the Hubble tension reflects new physics rather than a calibration offset.
Authors: This is an important conceptual point and we agree it deserves explicit treatment. The key distinction is that ΔM enters as a shift in the absolute magnitude of the distance indicator, which is degenerate with a change in d_L(z) only if that change is a constant multiplicative factor across all redshifts. The cross-correlation signal depends on the angular clustering pattern, which is sensitive to the shape of d_L(z) through the volume-redshift mapping, not just its overall normalization. Thus, a cosmological model that changes the shape of d_L(z) (e.g., through modified Ωm or early vs. late-universe H0) produces a distinguishable signal from a constant ΔM. However, we acknowledge that a cosmological model that mimics a constant rescaling of distances at the relevant redshifts would be partially degenerate with ΔM. We will add a dedicated discussion of this separability, including a quantitative assessment of the ΔM–H0 degeneracy from the Fisher matrix (the off-diagonal elements), to make the scope and limitations of the method transparent. revision: yes
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Referee: The assumption that a constant calibration offset ΔM is a sufficient model for calibration systematics should be justified. Real calibration systematics may be redshift-dependent, survey-dependent, or correlated with selection effects. If the true systematic has a non-constant form, a constant-ΔM fit could absorb or mask any calibration error. The manuscript should discuss the sensitivity of the forecasted constraints to this simplification, or at minimum state the regime in which a constant offset is a valid approximation.
Authors: The referee is correct that real calibration systematics are unlikely to be perfectly constant in redshift. The constant-ΔM model is presented as a first test case, chosen for clarity and because the Hubble tension corresponds to a roughly constant offset in the local distance ladder. We will add a discussion of the regime of validity: the constant-offset approximation is most appropriate when the calibration systematic is dominated by a zero-point error (e.g., in the Cepheid or SN Ia absolute magnitude calibration) that affects all redshifts similarly, which is precisely the scenario relevant to the Hubble tension. We will also note that the method can be generalized to a redshift-dependent ΔM(z) parametrization (e.g., a Taylor expansion or binned offsets), at the cost of increased parameter degeneracy and weakened constraints. We will include a qualitative discussion of how the forecasted precision degrades if ΔM is allowed to vary with redshift, and state explicitly that the constant-offset results represent an optimistic but well-motivated benchmark. revision: yes
Circularity Check
No circularity detected: the paper presents a Fisher forecast whose inputs (survey specs, cosmological model, nuisance parameters) are distinct from its outputs (forecasted constraints on ΔM and H0).
full rationale
This is an abstract-only review, so the full derivation chain cannot be walked in detail. However, from the abstract alone, no circularity is identifiable. The paper claims that angular cross-correlations between distance indicators and galaxy catalogues, interpreted within an assumed cosmological model, can constrain a calibration offset ΔM via Fisher forecasts. The inputs to this analysis are: (1) survey specifications (LSST SN Ia counts, DESI galaxy catalogue), (2) an assumed cosmological model, and (3) the cross-correlation signal structure. The outputs are forecasted constraints σ_ΔM ≈ 0.05 and σ_H0 ≈ 1.81. There is no indication in the abstract that ΔM is defined in terms of the cross-correlation it is meant to constrain, nor that the forecast precision is fitted to and then 'predicted' from the same data. The concern raised by the reader and skeptic — that the forecast precision depends on which nuisance parameters are marginalized over and that model assumptions could bias the result — is a correctness/robustness concern, not a circularity concern. The cosmological model is an input assumption, not an output being fed back as a prediction. Without the full text, no self-citation chain or definitional reduction can be exhibited. The honest finding is: no circularity detectable from available material.
Axiom & Free-Parameter Ledger
free parameters (3)
- ΔM (constant calibration offset)
- H0
- Survey parameters (N_SN, galaxy density, redshift range, sky coverage)
axioms (3)
- domain assumption Distance indicators trace the same large-scale structure as galaxies in redshift space, so their angular cross-correlation encodes cosmological information.
- ad hoc to paper A constant calibration offset ΔM shifts all observed distances by a multiplicative factor, which is a sufficient model for calibration systematics.
- domain assumption The assumed cosmological model correctly describes the clustering signal, so deviations can be attributed to ΔM.
Reference graph
Works this paper leans on
-
[1]
A. R. Sandage, Physics Today23, 34 (1970)
work page 1970
-
[2]
Tensions between the Early and the Late Universe
L. Verde, T. Treu, and A. G. Riess, Nature Astron.3, 891 (2019), arXiv:1907.10625 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2019
-
[3]
E. Di Valentinoet al.(CosmoVerse Network), Phys. Dark Univ.49, 101965 (2025), arXiv:2504.01669 [astro- ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2025
-
[4]
E. Abdallaet al., JHEAp34, 49 (2022), arXiv:2203.06142 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2022
-
[5]
A. G. Riesset al., Astrophys. J. Lett.934, L7 (2022), arXiv:2112.04510 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2022
-
[6]
Planck 2018 results. VI. Cosmological parameters
N. Aghanimet al.(Planck), Astron. Astrophys.641, A6 (2020), [Erratum: Astron.Astrophys. 652, C4 (2021)], arXiv:1807.06209 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2020
-
[7]
Hubble Tension: The Evidence of New Physics
J.-P. Hu and F.-Y. Wang, Universe9, 94 (2023), arXiv:2302.05709 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2023
-
[8]
New physics in light of the $H_0$ tension: an alternative view
S. Vagnozzi, Phys. Rev. D102, 023518 (2020), arXiv:1907.07569 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2020
-
[9]
Seven hints that early-time new physics alone is not sufficient to solve the Hubble tension
S. Vagnozzi, Universe9, 393 (2023), arXiv:2308.16628 [astro-ph.CO]. 8
work page internal anchor Pith review Pith/arXiv arXiv 2023
-
[10]
In the Realm of the Hubble tension $-$ a Review of Solutions
E. Di Valentino, O. Mena, S. Pan, L. Visinelli, W. Yang, A. Melchiorri, D. F. Mota, A. G. Riess, and J. Silk, Class. Quant. Grav.38, 153001 (2021), arXiv:2103.01183 [astro- ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2021
-
[11]
The tension in the absolute magnitude of Type Ia supernovae
D. Camarena and V. Marra, arXiv e-prints , arXiv:2307.02434 (2023), arXiv:2307.02434 [astro- ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2023
-
[12]
R. Camilleriet al.(DES), Mon. Not. Roy. Astron. Soc. 537, 1818 (2025), arXiv:2406.05049 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2025
-
[13]
A new method to build the (inverse) distance ladder
D. Camarena and V. Marra, Mon. Not. Roy. Astron. Soc. 495, 2630 (2020), arXiv:1910.14125 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2020
-
[14]
First principles calculation of the shift current photovoltaic effect in ferro- electrics,
M. Oguri, Physical Review D93, 10.1103/phys- revd.93.083511 (2016)
- [15]
-
[16]
Accurate precision Cosmology with redshift unknown gravitational wave sources
S. Mukherjee, B. D. Wandelt, S. M. Nissanke, and A. Silvestri, Phys. Rev. D103, 043520 (2021), arXiv:2007.02943 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2021
-
[17]
S. Mukherjee and B. D. Wandelt, preprint (2018), arXiv:1808.06615 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2018
-
[18]
M. L. Cross-Parkin, C. Howlett, L. Giani, C. Blake, and T. M. Davis, preprint (2026), arXiv:2605.06783 [astro- ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2026
-
[19]
A. Q. Cheng and J. Gair, preprint (2026), arXiv:2603.13053 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2026
- [20]
-
[21]
C. e. a. Blake, MNRAS418, 1725 (2011), arXiv:1108.2637 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2011
-
[22]
A. Lewis and A. Challinor, CAMB: Code for Anisotropies in the Microwave Background, Astrophysics Source Code Library, record ascl:1102.026 (2011), ascl:1102.026
work page 2011
-
[23]
R. A. Fisher, Phil. Trans. Roy. Soc. Lond. A222, 309 (1922)
work page 1922
-
[24]
Collaboration, The Astronomical Journal164, 207 (2022)
D. Collaboration, The Astronomical Journal164, 207 (2022)
work page 2022
-
[25]
E. C. Bellm, The zwicky transient facility (2014), arXiv:1410.8185 [astro-ph.IM]
work page internal anchor Pith review Pith/arXiv arXiv 2014
-
[26]
Measuring the growth rate of structure with Type IA Supernovae from LSST
C. Howlett, A. S. G. Robotham, C. D. P. La- gos, and A. G. Kim, Astrophys. J.847, 128 (2017), arXiv:1708.08236 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv 2017
-
[27]
LSST: from Science Drivers to Reference Design and Anticipated Data Products
ˇZ. Ivezi´ cet al.(LSST), Astrophys. J.873, 111 (2019), arXiv:0805.2366 [astro-ph]
work page internal anchor Pith review Pith/arXiv arXiv 2019
-
[28]
E. N. Tayloret al., The Messenger190, 46 (2023)
work page 2023
- [29]
-
[30]
D. Foreman-Mackey, D. W. Hogg, D. Lang, and J. Good- man, Publications of the Astronomical Society of the Pa- cific125, 306–312 (2013)
work page 2013
-
[31]
S. R. Hinton, The Journal of Open Source Software1, 00045 (2016)
work page 2016
-
[32]
Cross-correlating radial peculiar velocities and CMB lensing convergence
L. Giani, C. Howlett, R. Ruggeri, F. Bianchini, K. Said, and T. M. Davis, JCAP2023(5), 002, arXiv:2301.08381 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv
-
[33]
Beyond the traditional Line-of-Sight approach of cosmological angular statistics
N. Sch¨ oneberg, M. Simonovi´ c, J. Lesgourgues, and M. Zaldarriaga, JCAP2018(10), 047, arXiv:1807.09540 [astro-ph.CO]
work page internal anchor Pith review Pith/arXiv arXiv
-
[34]
M. LoVerde and N. Afshordi, Phys. Rev. D78, 123506 (2008), arXiv:0809.5112 [astro-ph]
work page internal anchor Pith review Pith/arXiv arXiv 2008
-
[35]
E. Krause and T. Eifler, Monthly Notices of the Royal Astronomical Society470, 2100–2112 (2017)
work page 2017
- [36]
-
[37]
C. R. Raoet al., Bull. Calcutta Math. Soc37, 81 (1945)
work page 1945
-
[38]
Cram´ er,Mathematical methods of statistics, Vol
H. Cram´ er,Mathematical methods of statistics, Vol. 9 (Princeton university press, 1999)
work page 1999
discussion (0)
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