pith. sign in

arxiv: 2511.04733 · v2 · submitted 2025-11-06 · 🌌 astro-ph.CO

Combining CMB datasets with consistent foreground modelling

M. Tristram , M. Douspis , A. Gorce , S. Henrot-Versill\'e , L. T. Hergt , S. Ilic , L. McBride , M. Mu\~noz-Echeverr\'ia
show 2 more authors
E. Pointecouteau L. Salvati
This is my paper

Pith reviewed 2026-05-18 00:39 UTC · model grok-4.3

classification 🌌 astro-ph.CO
keywords CMB cosmologyforeground modelingjoint analysisPlanckACTSPTneutrino constraintsLambdaCDM parameters
0
0 comments X

The pith

Combining Planck, ACT and SPT CMB data with shared foreground modeling leaves LambdaCDM parameters stable while widening neutrino uncertainties by up to 35 percent.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper builds a single likelihood that fits temperature and polarization spectra from Planck, the Atacama Cosmology Telescope, and the South Pole Telescope while modeling the cosmic microwave background, Galactic and extragalactic foregrounds, and instrumental effects together. This joint treatment reduces the impact of choosing any one foreground template. Standard six-parameter LambdaCDM results change very little across different foreground choices, which strengthens in those values. Parameters in extended models, especially neutrino mass, become less precise once foreground uncertainty is averaged over. The work shows that consistent foreground handling across current experiments is practical and will matter for tighter future measurements.

Core claim

We present a joint cosmological analysis combining data from the Planck satellite, the Atacama Cosmology Telescope, and the South Pole Telescope. We construct a unified likelihood that reproduces the measured temperature and polarisation power spectra by jointly modelling the cosmic microwave background (CMB) signal, Galactic and extragalactic foregrounds, and instrumental systematics across all datasets. Within this joint analysis, ΛCDM parameters exhibit remarkable stability with respect to variations in foreground modelling. Parameters for cosmological extensions are more sensitive to these assumptions, with uncertainties increasing by up to 35% in the neutrino sector after marginalising

What carries the argument

unified likelihood that jointly models the CMB signal, Galactic and extragalactic foregrounds, and instrumental systematics for Planck, ACT, and SPT datasets

If this is right

  • LambdaCDM parameters remain consistent when different foreground templates are substituted in the joint likelihood.
  • Uncertainties on parameters in cosmological extensions, such as the neutrino sector, increase by up to 35 percent once foreground models are marginalized over.
  • Foreground parameter values themselves change more noticeably with the choice of underlying foreground assumptions.
  • A fully joint analysis across multiple current CMB experiments is feasible when foregrounds receive consistent treatment.
  • Accurate foreground modeling is required to meet the science targets of next-generation high-sensitivity CMB surveys.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Future multi-experiment analyses may need to adopt similar unified modeling to avoid underestimating errors on extended parameters.
  • The observed robustness of LambdaCDM results suggests that foreground modeling differences alone are unlikely to explain existing cosmological tensions between datasets.
  • Consistent foreground treatment across instruments could improve cross-checks when CMB data are combined with other cosmological probes.

Load-bearing premise

The unified likelihood accurately reproduces the measured temperature and polarisation power spectra by jointly modelling the CMB signal, Galactic and extragalactic foregrounds, and instrumental systematics across the Planck, ACT, and SPT datasets.

What would settle it

Re-running the joint fit with an alternate foreground template set that produces LambdaCDM parameter shifts larger than the quoted uncertainties would falsify the stability claim.

Figures

Figures reproduced from arXiv: 2511.04733 by A. Gorce, E. Pointecouteau, L. McBride, L. Salvati, L. T. Hergt, M. Douspis, M. Mu\~noz-Echeverr\'ia, M. Tristram, S. Henrot-Versill\'e, S. Ilic.

Figure 1
Figure 1. Figure 1: Uncertainties on angular power spectra T T, T E, and EE for the Planck PR4 (red, Tristram et al. 2024), ACT DR6 (blue, Louis et al. 2025), and SPT-3G D1 (green, Camphuis et al. 2025) datasets compared to full-sky cosmic variance (dashed line). Uncertainties are averaged from all cross-frequency spec￾tra according to their respective covariance matrix. complex forms; see Mangilli et al. 2015), the large num… view at source ↗
Figure 2
Figure 2. Figure 2: Templates of CIB power spectrum normalised at [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 4
Figure 4. Figure 4: Templates of kSZ power spectrum normalised at [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figure 3
Figure 3. Figure 3: Templates of tSZ power spectrum normalised at [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 5
Figure 5. Figure 5: Templates of tSZ×CIB power spectrum normalised at ℓ0 = 3000 (black line: baseline template). with ξ the correlation coefficient scaling the template C tSZ×CIB ℓ . 5.7. Radio sources Radio sources are modelled with a flat Poisson power spectrum and a power-law spectral energy distribution, a radio ν = ν −βradio (Tucci et al. 2011). The SED index βradio is not well known and depends on the source population.… view at source ↗
Figure 6
Figure 6. Figure 6: presents a comparison of the posterior distributions for the ΛCDM parameters derived from Planck, ACT, SPT and their combination, using the coherent likelihood described in Sect. 2 and the baseline foreground templates (Sect. 5). Each dataset in￾corporates measurements from the T T, T E and EE power spec￾tra. Constraints on ΛCDM cosmological parameters are sum￾marised in [PITH_FULL_IMAGE:figures/full_fig_… view at source ↗
Figure 8
Figure 8. Figure 8: illustrates how the posterior distributions of the ΛCDM parameters change when different foreground templates are con￾sidered. We run several chains corresponding to different com￾binations of foreground spectra in order to assess how parameter estimates vary with the details of the foreground modelling. In practice, we vary only one foreground model at a time and then concatenate the resulting MCMC chains… view at source ↗
Figure 7
Figure 7. Figure 7: Posterior distributions for the ΛCDM cosmological pa￾rameters derived from the combination of Planck, ACT, and SPT, using T T, T E, EE power spectra and their combination. 6.3. Impact of foregrounds models [PITH_FULL_IMAGE:figures/full_fig_p007_7.png] view at source ↗
Figure 10
Figure 10. Figure 10: Posterior distributions for extragalactic foregrounds [PITH_FULL_IMAGE:figures/full_fig_p008_10.png] view at source ↗
Figure 9
Figure 9. Figure 9: Posterior distributions for the extragalactic parameters [PITH_FULL_IMAGE:figures/full_fig_p008_9.png] view at source ↗
Figure 12
Figure 12. Figure 12: Posterior distributions for extragalactic foregrounds [PITH_FULL_IMAGE:figures/full_fig_p009_12.png] view at source ↗
Figure 13
Figure 13. Figure 13: Posterior distributions for extragalactic foregrounds [PITH_FULL_IMAGE:figures/full_fig_p009_13.png] view at source ↗
Figure 15
Figure 15. Figure 15: Posterior distributions for extragalactic foregrounds [PITH_FULL_IMAGE:figures/full_fig_p010_15.png] view at source ↗
Figure 14
Figure 14. Figure 14: Posterior distributions for extragalactic foregrounds [PITH_FULL_IMAGE:figures/full_fig_p010_14.png] view at source ↗
Figure 16
Figure 16. Figure 16: Posterior distributions for AL (left), P mν (center), and Neff (right) combining Planck, ACT, and SPT, varying foreground templates as described in Sect. 7 (in gray) as compared to the posteriors after marginalisation over the foreground models (in red). (0.055 eV), indicating that the combined constraint is sensitive to the details of the foreground modelling. Compared to the Planck-only limit (see Annex… view at source ↗
Figure 17
Figure 17. Figure 17: shows the posterior for ΩK together with its ge￾ometric degeneracy with H0. As discussed in T24, with Planck PR4, the tail of the 2-d posterior in the H0–ΩK plane at low H0 and negative ΩK is significantly less preferred. Indeed, using the combined CMB datasets, averaging over foreground models, we 60 65 70 H0 0.03 0.02 0.01 0.00 k 0.02 0.00 k baseline marg [PITH_FULL_IMAGE:figures/full_fig_p011_17.png] view at source ↗
read the original abstract

We present a joint cosmological analysis combining data from the Planck satellite, the Atacama Cosmology Telescope, and the South Pole Telescope. We construct a unified likelihood that reproduces the measured temperature and polarisation power spectra by jointly modelling the cosmic microwave background (CMB) signal, Galactic and extragalactic foregrounds, and instrumental systematics across all datasets. We reduce reliance by combining datasets and improve the robustness of parameter estimation by marginalising over the choice of foreground templates. Within this joint analysis, $\Lambda$CDM parameters exhibit remarkable stability with respect to variations in foreground modelling. Parameters for cosmological extensions are more sensitive to these assumptions, with uncertainties increasing by up to 35% in the neutrino sector after marginalising over foreground models. In contrast, the determination of foreground parameters depends more strongly on the assumptions made about the underlying foreground models. Overall, this work demonstrates the feasibility and reliability of a fully joint analysis of current CMB experiments and emphasizes the importance of consistent and accurate foreground modelling for the scientific goals of next-generation, high-sensitivity CMB surveys.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 3 minor

Summary. The paper presents a joint cosmological analysis combining Planck, ACT, and SPT CMB datasets. It constructs a unified likelihood jointly modeling the CMB signal, Galactic/extragalactic foregrounds, and instrumental systematics, then marginalizes over foreground template choices. The central results are that ΛCDM parameters remain stable under these variations while parameters in cosmological extensions (particularly the neutrino sector) show uncertainties increasing by up to 35%, with foreground parameters themselves being more sensitive to modeling assumptions. The work concludes by highlighting the feasibility of such joint analyses for future high-sensitivity CMB surveys.

Significance. If the results hold, the manuscript makes a useful contribution by providing an explicit framework for consistent foreground modeling across multiple CMB experiments and demonstrating the impact of marginalization on parameter robustness. This is relevant for next-generation surveys. The manuscript supplies the explicit likelihood construction, template variations, and resulting posterior shifts, which aids reproducibility and allows direct scrutiny of the stability and uncertainty-inflation claims.

major comments (2)
  1. [§3] §3 (unified likelihood): the claim that the joint model accurately reproduces the measured temperature and polarization power spectra across all three datasets is load-bearing for the stability results; explicit validation tests comparing the joint posterior to separate Planck-only, ACT-only, and SPT-only constraints should be shown to confirm that no compensating biases are present.
  2. [Results section] Results on neutrino extensions: the reported up to 35% uncertainty increase is a key quantitative outcome supporting the claim that extension parameters are more sensitive; this must be tied to a specific table or figure that reports the before/after 1σ errors on the relevant parameter (e.g., ∑m_ν or N_eff) for each foreground template choice.
minor comments (3)
  1. [Abstract] The abstract describes ΛCDM parameters as exhibiting 'remarkable stability'; adding a quantitative metric (e.g., maximum fractional shift in best-fit values or overlap of credible intervals) would make this claim more precise and easier to evaluate.
  2. [Figures] Figure captions and legends should explicitly label which curves or contours correspond to each foreground template variation to improve readability of the marginalization results.
  3. [§2] A brief discussion of possible residual dataset overlaps or cross-calibration systematics between Planck, ACT, and SPT would strengthen the justification for the joint likelihood.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for the constructive comments, which have helped us improve the clarity and robustness of our presentation. We address each major comment below.

read point-by-point responses

  1. Referee: [§3] §3 (unified likelihood): the claim that the joint model accurately reproduces the measured temperature and polarization power spectra across all three datasets is load-bearing for the stability results; explicit validation tests comparing the joint posterior to separate Planck-only, ACT-only, and SPT-only constraints should be shown to confirm that no compensating biases are present.

    Authors: We agree that explicit validation of the joint model against individual dataset constraints is important to substantiate the stability claims and rule out compensating biases. In the revised manuscript we have added a new subsection (3.4) that directly compares the joint posterior distributions for both ΛCDM and neutrino-extension parameters against the separate Planck-only, ACT-only, and SPT-only constraints. These comparisons confirm consistency within the reported uncertainties and are now shown in a new Figure 5. revision: yes

  2. Referee: [Results section] Results on neutrino extensions: the reported up to 35% uncertainty increase is a key quantitative outcome supporting the claim that extension parameters are more sensitive; this must be tied to a specific table or figure that reports the before/after 1σ errors on the relevant parameter (e.g., ∑m_ν or N_eff) for each foreground template choice.

    Authors: We thank the referee for highlighting the need for explicit quantification. The up to 35% increase refers to the marginalised uncertainty on ∑m_ν (with a smaller but still notable increase for N_eff). This is now explicitly tied to Table 4, which reports the 1σ errors for each foreground template choice individually as well as the fully marginalised case. We have revised the relevant paragraph in the Results section to reference Table 4 directly and to quote the before/after values for both parameters. revision: yes

Circularity Check

0 steps flagged

No significant circularity detected

full rationale

The paper constructs a unified likelihood for joint modeling of CMB, Galactic/extragalactic foregrounds and systematics across independent Planck, ACT and SPT datasets, then reports empirical posterior results after marginalizing over foreground template choices. The claimed stability of ΛCDM parameters and up to 35% uncertainty inflation in the neutrino sector are direct outputs of this data-driven fit rather than any reduction by construction. No self-definitional steps, fitted inputs renamed as predictions, load-bearing self-citations, or smuggled ansatzes appear in the derivation chain; the analysis remains self-contained against external observational benchmarks.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The central claims rest on the ability to decompose observations into CMB plus foreground plus systematic components that remain consistent across instruments and on the assumption that marginalizing over template choices adequately captures modeling uncertainty without residual bias.

free parameters (1)
  • foreground template parameters
    The analysis explicitly marginalizes over the choice of foreground templates, implying these parameters are varied and integrated over rather than fixed.
axioms (1)
  • domain assumption CMB observations from different instruments can be jointly modeled as the sum of a common cosmic signal, instrument-specific systematics, and Galactic plus extragalactic foregrounds.
    This decomposition is invoked when constructing the unified likelihood that reproduces the measured power spectra.

pith-pipeline@v0.9.0 · 5765 in / 1494 out tokens · 48798 ms · 2026-05-18T00:39:24.114335+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

What do these tags mean?
matches
The paper's claim is directly supported by a theorem in the formal canon.
supports
The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends
The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses
The paper appears to rely on the theorem as machinery.
contradicts
The paper's claim conflicts with a theorem or certificate in the canon.
unclear
Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. The End of the First Act: Spectral Running, Interacting Dark Radiation, and the Hubble Tension in Light of ACT DR6 Data

    astro-ph.CO 2026-04 unverdicted novelty 5.0

    Including spectral running α_s, β_s and self-interacting dark radiation relaxes the ACT DR6 bound on ΔN_eff to <0.58 and lowers the Hubble tension to 2.2σ with three extra parameters.

Reference graph

Works this paper leans on

2 extracted references · 2 canonical work pages · cited by 1 Pith paper

  1. [1]

    Bolliet, A

    Addison, G. E., Dunkley, J., Hajian, A., et al. 2012a, ApJ, 752, 120 Addison, G. E., Dunkley, J., & Spergel, D. N. 2012b, MNRAS, 427, 1741 Akita, K. & Yamaguchi, M. 2020, J. Cosmology Astropart. Phys., 2020, 012 Battaglia, N., Bond, J. R., Pfrommer, C., & Sievers, J. L. 2012, ApJ, 758, 75 Battaglia, N., Bond, J. R., Pfrommer, C., Sievers, J. L., & Sijacki...

    work page arXiv 2020

  2. [2]

    60 80 H0 0.06 0.04 0.02 0.00 0.02 0.04 k 0.05 0.00 k ACT SPT Planck Planck+ACT+SPT Fig

    andΩ K =−0.044 +0.018 −0.015 fromPlikPR3 (Planck Collaboration VI 2020). 60 80 H0 0.06 0.04 0.02 0.00 0.02 0.04 k 0.05 0.00 k ACT SPT Planck Planck+ACT+SPT Fig. D.2: Posterior distributions forΩ K usingPlanck, ACT, or SPT, and their combination. Figure D.2 shows the posterior forΩ K together with its geometric degeneracy withH

    work page 2020