REVIEW 2 major objections 7 minor 38 references
The time delay between stellar birth and binary merger, not the details of how stars become compact remnants, controls the predicted gravitational-wave–galaxy cross-correlation signal.
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
T0 review · deepseek-v4-flash
2026-08-02 23:03 UTC pith:FFOU7LVO
load-bearing objection A useful, honest forecast that shows formation history—especially time delay—dominates GW×galaxy cross-correlation predictions, though the quantitative S/N values rest on a thin calibration. the 2 major comments →
The impact of the formation channel on gravitational-wave-galaxy cross-correlations
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The paper establishes that the progenitor-to-remnant time-delay distribution P(τ) ∝ 1/τ^α is the dominant astrophysical uncertainty shaping the GW-galaxy angular cross-correlation, while the mass-transfer function (rapid vs. delayed nova) is subdominant. Using mock GW catalogues normalized to a 600/yr current-generation detection rate, they show that changing α from 1.0 to 0.5 shifts the GW radial kernel to lower redshifts, boosting overlap with shallow galaxy catalogues and increasing the cumulative signal-to-noise from ~1 (undetectable) to ~10 for current-generation detectors cross-correlated with 2MPZ. Deeper catalogues such as Quaia are largely insensitive to the formation channel becaus
What carries the argument
The central object is the GW radial kernel φ_GW(χ), the normalized redshift distribution of detected mergers, built from population-synthesis simulations with a star-formation history, an initial mass function, and a delay function P(τ) = 1/τ^α. The cross-correlation power spectrum C_ℓ^{GW g} is computed via C_ℓ = b_g b ∫ dχ/χ² φ_GW(χ) φ_g(χ) P(z, k), with a per-SNR-bin beam factor B_{ρ,ℓ} that smears GW positions. The delay exponent α changes φ_GW, and the analysis shows that this change dominates over the mass-transfer function and over redshift uncertainties.
Load-bearing premise
The entire redshift-error model, which sets the uncertainty band that absorbs differences between mass-transfer functions, comes from a Bayesian fit to just 10 pilot events with sky position and orientation priors fixed to delta functions, and the authors note the fit is poor for next-generation events.
What would settle it
Compute the redshift errors δz(z) from a larger, more realistic set of GW parameter-estimation runs (or from observed events with electromagnetic counterparts), and re-evaluate whether the rapid and delayed nova kernels still fall within the uncertainty band. If the true δz is smaller by a factor of 2–3, the mass-transfer functions would become distinguishable, overturning the claim that they are negligible. Additionally, a direct measurement of the GW-galaxy cross-correlation with an O5-like catalogue at S/N ≈ 10 for long-delay models would confirm the central prediction, while a stronger-tha
If this is right
- If the delay distribution is not known, forecasts of the GW-galaxy bias or cosmological parameters from cross-correlations carry a systematic uncertainty that can be as large as the difference between detection and non-detection.
- Current-generation GW networks cross-correlated with shallow galaxy catalogues can only detect the signal if mergers are significantly delayed (small α); a null or weak detection would not rule out the signal but would point toward shorter delays.
- Next-generation detectors, despite detecting more events, may not improve the ability to distinguish formation channels via cross-correlation alone because their higher-redshift reach reduces overlap with shallow catalogues and deep catalogues wash out the differences.
- Comparing current- and next-generation cross-correlation amplitudes can provide a handle on the delay distribution, since the ratio of signals changes by up to three orders of magnitude depending on α.
- The mass-transfer function can be effectively ignored in cross-correlation forecasts, simplifying population-synthesis modeling for this observable.
Where Pith is reading between the lines
- One testable extension: with a few years of current-generation data, measuring the cross-correlation amplitude and its scale dependence against a 2MPZ-like catalogue would directly constrain α; if the signal is not seen at the level predicted for α ≤ 0.75, short delays are favoured.
- The paper's result suggests that using a deep photometric catalogue like Quaia to measure the GW bias is robust to formation-channel assumptions, making it a safer target for cosmological inference, but at the cost of lower detection significance.
- The redshift-error relation, fitted to only 10 events with fixed sky-position priors, may underestimate true localization uncertainties; if so, the claimed separability of α=1.0 from α=0.95 at low redshift (which relies on the error band) could be degraded, strengthening the paper's core conclusion about degeneracy.
- A natural next step is to include electromagnetic counterparts or host-galaxy identifications for a subset of events; the paper itself notes this would break the mass-transfer degeneracy, and the same data would also shrink redshift errors, sharpening time-delay constraints.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This paper studies how two properties of the binary formation channel — the progenitor-to-remnant mass-transfer function (rapid vs delayed supernova engines) and the time-delay distribution between formation and merger, parameterised as P(τ) ∝ τ^{-α} with α = 1, 0.95, 0.75, 0.5 — affect the predicted gravitational-wave–galaxy angular cross-correlation. The authors generate five mock GW catalogues from population-synthesis simulations, normalise them to a 600/yr HLV O5 rate, compute GW radial kernels, apply redshift errors estimated from a 10-event pilot, and cross-correlate with galaxy kernels modelled on 2MPZ and Quaia. The main findings are that the mass-transfer function leaves the GW kernel within the redshift-error band, while the time-delay exponent strongly changes the kernel and hence the cross-spectrum, especially for the shallow 2MPZ catalogue. For current-generation detectors, only the longest delays (α = 0.75, 0.5) give a detectable 2MPZ cross-correlation, whereas all Quaia cross-correlations are marginally detectable or consistent with zero. The authors conclude that forecasts of cosmological or astrophysical parameters from GW×galaxy cross-correlations must be conditioned on the assumed delay distribution.
Significance. The paper provides a useful, clearly presented exploration of how two formation-channel parameters propagate into a standard GW×galaxy forecast. Its main strength is the systematic side-by-side comparison using a common pipeline, with an honest acknowledgement of limitations (e.g., "exploratory results", the poor $\chi^2$ of the next-generation redshift-error fit). The time-delay result — that α strongly affects the cross-correlation — is robust and, while expected from the construction of the radial kernels, is quantified here for realistic survey parameters and is likely to survive improvements in input assumptions. The Quaia insensitivity and the current-generation detection prospects for long delays are also plausibly robust. However, the second headline claim (mass transfer has negligible effect) rests on a fragile redshift-error calibration, and the quantitative S/N values inherit several unquantified modelling choices. If the results hold, the paper is a valuable caution for the interpretation of future GW×galaxy measurements.
major comments (2)
- [§3.1.1, Fig. 3] The claim that the mass-transfer function has negligible effect is established only through the redshift-error band from the adopted δz(z) relation, but the uncertainty on that relation is never propagated. The relation is fitted to a pilot catalogue of only 10 events with sky position and orientation priors fixed to delta functions [34], and the authors state "the fit is not very good for next-generation events" yet keep it as the working fit. The blue band in Fig. 3 is therefore itself uncertain; a factor ~2 reduction in its amplitude — plausible if a larger pilot or full marginalisation gives smaller distance errors — would shrink the band below the separation between catalogues 6 and 7, making the kernels distinguishable and flipping the "negligible" conclusion. This is load-bearing for the abstract. Please add a sensitivity analysis (bootstrap over the pilot, rescaling of δz, or mar
- [§4, Eq. (2.5)] The quoted cumulative S/N values inherit several unquantified modelling choices: the 97% SNR containment cut, the f_Res normalisation (600/yr), the beam scaling σ(ρ) ∝ 1/ρ, and the δz(z) relation. The paper states that varying the containment cut between 95% and 98% has an "appreciable effect" on the cross-correlations but does not show this, and no error budget for the S/N is provided. Consequently, numbers such as "S/N ~1 for catalogues 6 and 7 and ~10 for catalogues 9 and 11" should be presented as indicative conditional estimates, not as robust predictions. I recommend adding a supplementary figure or table showing how the cumulative S/N changes under the range of these choices.
minor comments (7)
- [Typesetting] Fig. 3 caption: "dshed" should be "dashed". There is also a stray "In" at the end of the text after Fig. 2. Please proofread.
- [Eq. (2.4)] The bias product is written as "bb_g"; this is ambiguous. If it denotes b_GW b_g, please make the subscripts explicit.
- [Fig. 2] The χ² and R² values quoted in the text are not defined in the figure or caption. Please clarify which fit to which data they refer to.
- [§3.1.1] The sentence "we made a pilot GW catalogue of 10 events drawn from the total simulated sample for catalogue 6, excluding the events in catalogue 6 themselves" is confusing. Please rephrase.
- [§3.1.2] The range 10^{-0.5} ≤ σ ≤ 10^{0.5} would be clearer with units (degrees).
- [§3.1.1] The statement that the 95–98% containment cut has "an appreciable effect" but less than α=1.00→0.95 is not shown quantitatively. A short supplementary figure would make this verifiable.
- [§5] The phrase "the most extreme cases with a very long time-delay function" is vague; specify α = 0.5 and 0.75 where appropriate.
Circularity Check
No significant circularity: forward-model sensitivity study; conclusions follow from assumed inputs but no fitted parameter is presented as an independent prediction.
full rationale
This paper is a forward-model sensitivity study, not an inverse inference. The authors specify population-synthesis inputs (SFR, IMF, mass-transfer, P(tau)=1/tau^alpha), simulate GW catalogues, compute radial kernels, and evaluate C_l^GWg through Eq. (2.4). The finding that the time-delay exponent alpha changes the cross-correlation is the intended propagation of an assumed input into the observable, not a fitted parameter being renamed as a prediction. No parameter is fitted to the cross-correlation data and then "predicted" back; the paper does not attempt to measure alpha or the mass-transfer function from the XC. The f_Res normalisation is anchored to the O5 600/yr rate, but the paper explicitly states this does not force next-generation rates and that the current-to-next-generation ratio is unaffected, so the Table 1 next-generation rates are genuine model predictions with independent content. The mass-transfer null result (catalogues 6 vs 7) relies on the delta-z(z) error band from a 10-event pilot catalogue; the authors acknowledge the next-generation fit is not good and keep it as their working fit (Section 3.1.1, footnote 6). This is a statistical robustness caveat, not circularity: the delta-z relation is fitted to a pilot catalogue, not to the kernel difference it is used to judge. There are no load-bearing self-citations: the formalism is cited to the external Calore et al. work, and the authors of the present paper are not among those authors. No uniqueness theorem is imported from the authors' prior work, and the power-law delay is presented as an explicit free assumption rather than as a derived result. The paper is also benchmarked against real external catalogues (2MPZ, Quaia) and public codes (pyccl, bilby, dynesty), further supporting that the central content is independent of the paper's own conclusions. Overall, no circular step satisfying the quoted-reduction criterion can be identified.
Axiom & Free-Parameter Ledger
free parameters (7)
- Time-delay exponent α =
0.50, 0.75, 0.95, 1.00 (four values)
- Detection-rate normalisation f_Res =
14.634, 13.636, 8.000, 1.000, 0.307 (×10^-5, Table 1)
- Redshift-error relation coefficients =
a=1.36, b=−0.44 (HLV); a=0.93, b=−1.46 (ET2CE)
- Beam scale σ(ρ) =
normalised at GW170817: ρ=32.4, σ≈1.4 deg
- SNR containment cut (97%) =
97% (varied 95–98%)
- Detection SNR thresholds =
ρ≥8 (HLV), ρ≥12 (ET2CE)
- Minimum delay times =
50/20/30 Myr (BHBH/NSNS/BHNS)
axioms (5)
- domain assumption Fixed flat ΛCDM (Ωc=0.25, Ωb=0.05, σ8=0.81, ns=0.96, h=0.67, no massive neutrinos)
- domain assumption Isolated binary evolution is the only formation channel; dynamical formation neglected
- domain assumption GW and galaxy overdensities are linearly biased tracers; GW bias is a constant multiplicative factor
- ad hoc to paper Delay distribution is a power law P(τ)=1/τ^α with α∈[0.5,1]
- domain assumption Fixed Madau-Dickinson SFR and Kroupa IMF, with IMF uncertainty folded into the multiplicative f_Res
read the original abstract
The angular, harmonic cross-correlation between gravitational wave (GW) events and galaxy catalogues contains rich information on the large-scale structure and the origin of compact binary mergers. In this work, we study how uncertainties in the binary formation channel affect the predicted cross-correlation signal for both current-generation and next-generation networks of detectors. We generate five mock GW catalogues for which we vary the progenitor-to-remnant mass-transfer function and the time-delay probability distribution between progenitor and remnant. We then cross-correlate these catalogues with galaxy samples modelled on the 2MASS Photometric Redshift catalogue (2MPZ) and the Gaia-unWISE quasar catalogue (Quaia). We find that the mass-transfer function has negligible effect on the cross-correlation signal, with differences remaining within redshift uncertainties. In contrast, the time-delay distribution dramatically affects the redshift distribution of the GW events and, with it, the cross-correlation signal, particularly for shallow galaxy catalogues. In particular, current-generation facilities can achieve significant detections only for the longest time delays when cross-correlated with 2MPZ, whilst all cross-correlations with the deeper Quaia catalogue are marginally detectable or consistent with zero. Our exploratory results thus demonstrate that forecasts on cosmological or astrophysical parameters derived from GW-galaxy cross-correlations are, as expected, strongly sensitive to the assumed binary formation history.
Reference graph
Works this paper leans on
-
[3]
I. Mandel and R.J.E. Smith,GW200115: A Nonspinning Black Hole–Neutron Star Merger, Astrophys. J. Lett.922(2021) L14 [2109.14759]. [4]KAGRA, VIRGO, LIGO Scientificcollaboration,GWTC-3: Compact Binary Coalescences Observed by LIGO and Virgo during the Second Part of the Third Observing Run,Phys. Rev. X13(2023) 041039 [2111.03606]
Pith/arXiv arXiv 2021
-
[5]
A. Raccanelli, E.D. Kovetz, S. Bird, I. Cholis and J.B. Munoz,Determining the progenitors of merging black-hole binaries,Phys. Rev. D94(2016) 023516 [1605.01405]
Pith/arXiv arXiv 2016
-
[6]
G. Scelfo, N. Bellomo, A. Raccanelli, S. Matarrese and L. Verde,GW×LSS: chasing the progenitors of merging binary black holes,JCAP09(2018) 039 [1809.03528]
Pith/arXiv arXiv 2018
-
[7]
F. Calore, A. Cuoco, T. Regimbau, S. Sachdev and P.D. Serpico,Cross-correlating galaxy catalogs and gravitational waves: a tomographic approach,Phys. Rev. Res.2(2020) 023314 [2002.02466]
Pith/arXiv arXiv 2020
-
[8]
S. Libanore, M.C. Artale, D. Karagiannis, M. Liguori, N. Bartolo, Y. Bouffanais et al., Gravitational Wave mergers as tracers of Large Scale Structures,JCAP02(2021) 035 [2007.06905]
Pith/arXiv arXiv 2021
-
[9]
S. Libanore, M. Liguori and A. Raccanelli,Signatures of primordial black holes in gravitational wave clustering,JCAP08(2023) 055 [2306.03087]
Pith/arXiv arXiv 2023
-
[10]
A. Pedrotti, M. Mancarella, J. Bel and D. Gerosa,Cosmology with the angular cross-correlation of gravitational-wave and galaxy catalogs: forecasts for next-generation interferometers and the Euclid survey,2504.10482
-
[11]
F. Santoliquido, M. Mapelli, Y. Bouffanais, N. Giacobbo, U.N. Di Carlo, S. Rastello et al.,The cosmic merger rate density evolution of compact binaries formed in young star clusters and in isolated binaries,Astrophys. J.898(2020) 152 [2004.09533]
Pith/arXiv arXiv 2020
-
[12]
F. Santoliquido, M. Mapelli, N. Giacobbo, Y. Bouffanais and M.C. Artale,The cosmic merger rate density of compact objects: impact of star formation, metallicity, initial mass function and binary evolution,Mon. Not. Roy. Astron. Soc.502(2021) 4877 [2009.03911]
Pith/arXiv arXiv 2021
-
[13]
Belczynski et al.,The Effect of Pair-Instability Mass Loss on Black Hole Mergers,Astron
K. Belczynski et al.,The Effect of Pair-Instability Mass Loss on Black Hole Mergers,Astron. Astrophys.594(2016) A97 [1607.03116]
Pith/arXiv arXiv 2016
-
[14]
K. Belczynski, D.E. Holz, T. Bulik and R. O’Shaughnessy,The first gravitational-wave source from the isolated evolution of two 40-100 Msun stars,Nature534(2016) 512 [1602.04531]
Pith/arXiv arXiv 2016
-
[15]
J. Hong, E. Vesperini, A. Askar, M. Giersz, M. Szkudlarek and T. Bulik,Binary Black Hole Mergers from Globular Clusters: the Impact of Globular Cluster Properties,Mon. Not. Roy. Astron. Soc.480(2018) 5645 [1808.04514]
Pith/arXiv arXiv 2018
-
[16]
S. Torniamenti, S. Rastello, M. Mapelli, U.N. Di Carlo, A. Ballone and M. Pasquato,Dynamics of binary black holes in young star clusters: the impact of cluster mass and long-term evolution,Mon. Not. Roy. Astron. Soc.517(2022) 2953 [2203.08163]
Pith/arXiv arXiv 2022
-
[17]
M. Gr¨ obner, W. Ishibashi, S. Tiwari, M. Haney and P. Jetzer,Binary black hole mergers in AGN accretion discs: gravitational wave rate density estimates,Astron. Astrophys.638(2020) A119 [2005.03571]
Pith/arXiv arXiv 2020
-
[18]
S. Stevenson and T. Clarke,Constraints on the contributions to the observed binary black hole population from individual evolutionary pathways in isolated binary evolution,2210.05040
-
[19]
P. Madau and M. Dickinson,Cosmic Star Formation History,Ann. Rev. Astron. Astrophys.52 (2014) 415 [1403.0007]. – 15 –
Pith/arXiv arXiv 2014
-
[20]
Kroupa,On the variation of the initial mass function,Mon
P. Kroupa,On the variation of the initial mass function,Mon. Not. Roy. Astron. Soc.322 (2001) 231 [astro-ph/0009005]
Pith/arXiv arXiv 2001
-
[21]
J.A. de Freitas Pacheco, T. Regimbau, S. Vincent and A. Spallicci,Expected coalescence rates of ns-ns binaries for laser beam interferometers,Int. J. Mod. Phys. D15(2006) 235 [astro-ph/0510727]
Pith/arXiv arXiv 2006
-
[22]
Fryer, K
C.L. Fryer, K. Belczynski, G. Wiktorowicz, M. Dominik, V. Kalogera and D.E. Holz,Compact remnant mass function: Dependence on the explosion mechanism and metallicity,The Astrophysical Journal749(2012) 91
2012
-
[23]
L. Boco, A. Lapi, M. Chruslinska, D. Donevski, A. Sicilia and L. Danese,Evolution of Galaxy Star Formation and Metallicity: Impact on Double Compact Objects Mergers,Astrophys. J. 907(2021) 110 [2012.02800]
Pith/arXiv arXiv 2021
-
[24]
G. Scelfo, L. Boco, A. Lapi and M. Viel,Exploring galaxies-gravitational waves cross-correlations as an astrophysical probe,JCAP10(2020) 045 [2007.08534]
Pith/arXiv arXiv 2020
-
[25]
C. Pellouin, I. Dvorkin and L. Lehoucq,Evolutionary tracks of binary neutron star progenitors across cosmic times,Astron. Astrophys.693(2025) A283 [2411.04563]
Pith/arXiv arXiv 2025
-
[26]
S. Mukherjee, T. Broadhurst, J.M. Diego, J. Silk and G.F. Smoot,Impact of astrophysical binary coalescence time-scales on the rate of lensed gravitational wave events,Mon. Not. Roy. Astron. Soc.506(2021) 3751 [2106.00392]
Pith/arXiv arXiv 2021
-
[27]
S. Afroz, Navdha and S. Mukherjee,Are all Binary Black Holes Detected by LIGO-Virgo-KAGRA Following the Universal Time-Delay Distributions? Probably Not, 2510.06352
-
[28]
P. Kroupa,The Initial mass function of stars: Evidence for uniformity in variable systems, Science295(2002) 82 [astro-ph/0201098]
Pith/arXiv arXiv 2002
-
[29]
P. Kroupa, E. Gjergo, T. Jerabkova and Z. Yan,The initial mass function of stars,2410.07311
-
[30]
R. Dave,The galaxy stellar mass-star formation rate relation: Evidence for an evolving stellar initial mass function?,Mon. Not. Roy. Astron. Soc.385(2008) 147 [0710.0381]
Pith/arXiv arXiv 2008
-
[31]
van Dokkum,Evidence of Cosmic Evolution of the Stellar Initial Mass Function,Astrophys
P. van Dokkum,Evidence of Cosmic Evolution of the Stellar Initial Mass Function,Astrophys. J.674(2008) 29 [0710.0875]
Pith/arXiv arXiv 2008
-
[32]
V. Baibhav, E. Berti, D. Gerosa, M. Mapelli, N. Giacobbo, Y. Bouffanais et al., Gravitational-wave detection rates for compact binaries formed in isolation: LIGO/Virgo O3 and beyond,Phys. Rev. D100(2019) 064060 [1906.04197]
Pith/arXiv arXiv 2019
-
[33]
R.W. Kiendrebeogo et al.,Updated Observing Scenarios and Multimessenger Implications for the International Gravitational-wave Networks O4 and O5,Astrophys. J.958(2023) 158 [2306.09234]
Pith/arXiv arXiv 2023
-
[34]
C. Pankow, L. Sampson, L. Perri, E. Chase, S. Coughlin, M. Zevin et al.,Astrophysical Prior Information and Gravitational-wave Parameter Estimation,Astrophys. J.834(2017) 154 [1610.05633]
Pith/arXiv arXiv 2017
-
[35]
M. Bilicki, T.H. Jarrett, J.A. Peacock, M.E. Cluver and L. Steward,2MASS Photometric Redshift catalog: a comprehensive three-dimensional census of the whole sky,Astrophys. J. Suppl.210(2014) 9 [1311.5246]
Pith/arXiv arXiv 2014
-
[36]
K. Storey-Fisher, D.W. Hogg, H.-W. Rix, A.-C. Eilers, G. Fabbian, M.R. Blanton et al.,Quaia, the Gaia-unWISE Quasar Catalog: An All-sky Spectroscopic Quasar Sample,Astrophys. J.964 (2024) 69 [2306.17749]
Pith/arXiv arXiv 2024
-
[37]
N. Koukoufilippas, D. Alonso, M. Bilicki and J.A. Peacock,Tomographic measurement of the intergalactic gas pressure through galaxy–tSZ cross-correlations,Mon. Not. Roy. Astron. Soc. 491(2020) 5464 [1909.09102]. – 16 –
Pith/arXiv arXiv 2020
-
[38]
Vallenari, A.G.A
A. Vallenari, A.G.A. Brown, T. Prusti, J.H.J. de Bruijne, F. Arenou, C. Babusiaux et al., Gaiadata release 3: Summary of the content and survey properties,Astronomy & Astrophysics 674(2023) A1
2023
-
[39]
A.M. Meisner, D. Lang, E.F. Schlafly and D.J. Schlegel,unWISE Coadds: The Five-year Data Set,Publ. Astron. Soc. Pac.131(2019) 124504 [1909.05444]
Pith/arXiv arXiv 2019
-
[40]
D. Alonso, G. Fabbian, K. Storey-Fisher, A.-C. Eilers, C. Garc ´ ıa-Garc ´ ıa, D.W. Hogg et al., Constraining cosmology with the Gaia-unWISE Quasar Catalog and CMB lensing: structure growth,JCAP11(2023) 043 [2306.17748]
Pith/arXiv arXiv 2023
-
[41]
D. Alonso, M. Nikjoo, A.I. Renzini, E. Bellini and P.G. Ferreira,Tomographic constraints on the production rate of gravitational waves from astrophysical sources,Phys. Rev. D110(2024) 103544 [2406.19488]. – 17 –
Pith/arXiv arXiv 2024
discussion (0)
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